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2020.0384.PR0014 1102 Rhoton Rd Land Use Permit App Plans Yelm3373383353363373323333343293313283283283333343353 3 6 32933133232 8 328329327328337338338335336337331332333334329328 330330330TSTSTSTSTSTSTSTSTSTSTSTSTSTSTSTSTBTBTBTBTBTBTBTBTBTBTBTBTBTBTBTBX X X X X X X AS BUILT CENTERLINEGRAVEL DRIVEWAY DIS T U R B E D D R I V E W A Y 40" FIR 27" FIR40" FIR 18" FIR 46" FIR 28" FIR 30" FIR 11" FIR 21" FIR 28" FIR 24" FIR 26" FIR 30" FIR 32" FIR 22" FIR 48" FIR 28" FIR 24" FIR 28" FIR 20" FIR 26" FIR 19" FIR 28" FIR 16" FIR 16" FIR 22" FIR 22" FIR 24" FIR 32" FIR 15" FIR 15" FIR RHOTON ROADS 89°28'57" W 2653.34' S 89°53'29" W 418.30'258.35 ' 2294.54'240.00'N 00°06'31" W2644.20'17 2019 18 T R 17N 02 19 E THURSTON COUNTY PARCEL NO. 64300800301. 1102 RHOTON RD SE LOT 1 SS-00-8255-YL FOUND 5/8" REBAR W/ CAP LS 24227 FOUND 1/2" REBAR W/ PUSHED OVER CAP FOUND 1/2" REBAR W/ PUSHED OVER CAP PP FOUND 5/8" REBAR W/ CAP LS 24227 30' NE CORNER OF SECTION 19 CALCULATED PER SURVEY REFERENCE 1 CENTER 1/4 CORNER OF SECTION 19 FOUND CASED MONUMENT W/ 2" BRASS DISC W/ PUNCH LS 22346 N 1/4 CORNER OF SECTION 19 FOUND 1/2" IRON PIPE W/ MPK BENCH MARK = 328.82'S 20°22 '43" E UAIL MEADOWS CT SE 946 QUAIL MEADOW CT SE 104 RHOTON CT NW 945 QUAIL MEADOW CT SE 22718430300 9246 RHOTON RD 64300800302 1002 RHOTON RD SE RHOTON ROADCULLENSROADKILLIONROADIIIIIIIIIIIIIIIIC A N A L RO A D C AN A L R O A D PROJECT SITE YELM CEN T R A L I A CA N A L YE L M C R E E K NISQUALLY RIVER YELM WA 1002 NW RHOTON ROAD YELM, WA 98597 SITE PLAN TPN 64300800301 & 64300800302 5016 Lacey Boulevard SE, Lacey, Washington 98503 (360) 491-3399 Fax (360) 491-3857 MODERN RESOURCES LLC SITE DEVELOPMENT VERTICAL DATUM NAVD 88 The information included on this map has been compiled by Thurston County staff from a variety of sources and is subject to change without notice. Additional elements may be present in reality that are not represented on the map. Ortho-photos and other data may not align. The boundaries depicted by these datasets are approximate. This document is not intended for use as a survey product. ALL DATA IS EXPRESSLY PROVIDED ‘AS IS’ AND ‘WITH ALL FAULTS’. Thurston County makes no representations or warranties, express or implied, as to accuracy, completeness, timeliness, or rights to the use of such information. In no event shall Thurston County be liable for direct, indirect, incidental, consequential, special, or tort damages of any kind, including, but not limited to, lost revenues or lost profits, real or anticipated, resulting from the use, misuse or reliance of the information contained on this map. If any portion of this map or disclaimer is missing or altered, Thurston County removes itself from all responsibility from the map and the data contained within. The burden for determining fitness for use lies entirely with the user and the user is solely responsible for understanding the accuracy limitation of the information contained in this map. Authorized for 3rd Party reproduction for personal use only. 300 Foot Radius 12,694Scale 1: 0 12/15/2020 Note: A map showing the project site and 300 foot radius Legend 500 1000 Feet Published: Map Created Using GeoData Public Website Parcel Boundaries Roads - Major (Large Scale) <all other values> I 5 ACCESS; US 101 ACCESS; US 101 SB OFF RAMP I 5; US 101 Roads (Large Scale) Railroads County Border Olympia Municipal Airport Water Bodies (River - Small Scale) Water Bodies (Other) Parks Cities Capital Forest County Background Roads - Major <all other values> I 5 ACCESS; US 101 ACCESS; US 101 SB OFF RAMP I 5; US 101 Roads Railroads County Border Olympia Municipal Airport Water Bodies (River - Small Scale) Water Bodies (Other) 2020©Thurston County Owner Name Mailing Address City State Zip Code Parcel Number COWLES-PORTERFIELD, RUTH A PO BOX 525 YELM WA 98597 22718430300 THE OESER COMPANY PO BOX 156 BELLINGHAMWA 98227 22719210700 KINGSVIEW DIV 3 HOMEOWNERS ASSN PO BOX 2506 KIRKLAND WA 98083 57630100000 ABBOTT, RICKY & ELIZABETH J 15946 QUAIL MEADOWS CT SEYELM WA 98597 57630100100 SMITH, HOLLY A 15942 QUAIL MEADOWS CT SEYELM WA 98597 57630100200 REE, ANTHONY H & KIMBERLEE K 15938 QUAIL MEADOWS CT SEYELM WA 98597 57630100300 NEMETH, MATTHEW & JAMIE S 15934 QUAIL MEADOWS CT SEYELM WA 98597 57630100400 THORNTION, DENNIS W & LISA M 15930 QUAIL MEADOWS CT SEYELM WA 98597 57630100500 REE, ANTHONY W 15929 QUAIL MEADOWS CT SEYELM WA 98597 57630101600 WINCHELL, JAHKEITH & COURTNEY 15933 QUAIL MEADOWS CT SEYELM WA 98597 57630101700 MICHELS, JOSEPH & MICHELLE 15937 QUAIL MEADOWS CT SEYELM WA 98597 57630101800 FISCHER, JORDAN A 15941 QUAIL MEADOWS CT SEYELM WA 98597 57630101900 SLAPE, INEZ D 15945 QUAIL MEADOWS CT SEYELM WA 98597 57630102000 SHIPPENTOWER, EDMOND L 1107 RHOTON CT YELM WA 98597 57660003700 BRADLEY, WILLIAM E 1106 RHOTON CT NWYELM WA 98597 57660003800 PFLUGMACHER, LINDA 1105 NW RHOTON CTYELM WA 98597 57660003900 ANDERSON, KARL W & CHRISTINE I 1104 RHOTON CT NWYELM WA 98597-975057660004000 BERLIN, JENNIFER 1119 RHOTON CT NWYELM WA 98597 57660004100 JANSEN, CHRIS J & NANCY M 754 111TH ST S TACOMA WA 98444-562057660004200 ZATKOVICH, CINDY A 1117 RHOTON CT NWYELM WA 98597 57660004300 MODERN RESOURCES LLC 4810 RACCOON VALLEY RD SEOLYMPIA WA 98513 64300800301 MODERN RESOURCES LLC 4810 RACCOON VALLEY RD SEOLYMPIA WA 98513 64300800302 OREAR, CANDY 730 SW INDUSTRIAL WAYBEND OR 97702 64300800303 YELM, CITY OF 106 2ND ST SE YELM WA 98597-766764300900400 MODERN RESOURCES LCC 4810 Raccoon Valley Rd SE Olympia, WA 98513 RE: Land Use Permit for 1102 Rhoton Rd To whom it may concern, Modern Resources LCC is developing the property located on 1102 Rhoton Rd in the City of Yelm, WA. Modern Resources respectfully request the City of Yelm defer installation of all frontage improvements to a later date. Following the Cities determination, Modern Resources will proceed as outline in Section 4B.080 (C) in negotiating commercial issues associated with a deferral. Respectfully, Emmanuel Mupinganjira PO Box 2834, Olympia, WA 98507 | 360.790.5936 September 20, 2020 Mr. Emmanuel Mupinganjira emmanuelm@moderncw.com Subject: Mazama Pocket Gopher Screening, Thurston County Tax Parcel Numbers 64300800301 and 64300800302; Yelm, Washington Dear Mr. Emmanuel Mupinganjira: This letter summarizes the Mazama pocket gopher (Thomomys Mazama) survey conducted by Capital Land & Water, LLC., for the subject property, Thurston County Tax Parcel Numbers 64300800301 and 64300800301 located at 1102 and 1002 Rhoton Road S.E. in incorporated Yelm, Washington (also herein referred to as the “study area”). This screening was conducted at your request to collect necessary information and evaluate the site as part of your purchase and development planning process. The purpose of the survey was to conduct a screening level assessment of potential pocket gopher occupancy and habitat as indicated by the presence/absence of mounds, other indicators observable during site inspections, and other available information. One preliminary field visit and two field surveys involving uniform transects to inspect for signs of potential Mazama pocket gopher activity were conducted. Existing data and observations do not indicate occurrences, habitation, or active use by pocket gophers. Based on this screening we have determined that Mazama pocket gophers are unlikely to be present and therefore are not likely to be affected by property development such as typical commercial or industrial building construction. This letter is intended to assist you and City of Yelm reviewers in land use and/or development planning and permitting decisions for the subject parcels. The U.S. Fish and Wildlife Service (USFWS) is the Federal agency with jurisdictional authority of Mazama pocket gopher protection according to the Endangered Species Act (ESA). Regulatory Context Mazama pocket gopher is a federal- and state-listed sensitive species protected by the (ESA), local (City of Yelm) Critical Areas code, and Washington State Department of Fish and Wildlife regulations and policies. The City of Yelm regulates development proposals according to Yelm municipal code including Section 18.21.110, Fish and Wildlife Habitat Conservation Areas. Mr. Emmanuel Mupinganjira September 20, 2020 CAPITAL LAND & WATER Page 2 To assess potential occupancy and presence of regulated Fish and Wildlife Habitat Conservation Areas for Mazama pocket gopher, Capital Land and Water used Thurston County policy related to development permitting review which includes a screening protocol 1 used to assess the likelihood of “take” of three subspecies of Mazama pocket gopher protected by the ESA. The screening methods are generally consistent with USFWS guidance for assessing take,2 which was also used in conducting this survey. The USFWS has jurisdictional authority over the protection of ESA-listed threatened Mazama pocket gopher and is ultimately responsible for decisions regarding the take of individuals and their habitat. Habitat Assessment The mapped soil types comprising the entire study area is Spanaway gravelly sandy loam, 0 to 3 percent slopes and 3 to 15 percent slopes. This soil type is classified as “more preferred,” indicating the potential for Mazama pocket gopher individuals or habitat to be present 3. However, overall conditions on the site range from unsuitable to marginal in terms of potential use. Potential habitat is limited due to forested areas and brushy areas characterized by woody shrubs including Scot’s broom (Cytisus scoparius). Other marginal conditions or limiting factors include sloped and hummocky terrain existing and historical roads (visible in historical aerial imagery), relative fragmentation/isolation from suitable habitats by surrounding development, lack of nearby water sources, limited food sources, and frequent predation as evident from signs of mound disturbance and wildlife trails observed during the surveys. The site is littered with debris indicating occasional human activity. There are unimproved access roads and informal trails potentially used by both humans and animals. Mounds and burrows observed on the site appear to be concentrated in a few small patches within the parcels; not evenly distributed. This pattern along with the dense shrubs and terrain throughout the site, and observations indicative of moles and rabbits, suggest that the site may not be suitable for, or used by, Mazama pocket gophers and burrows present are likely associated with other burrowing and ground dwelling animals. As part of the screening, we also referenced Washington State Department of Fish and Wildlife’s priority habitat and species (PHS) database prior to inspections to identify any previously documented known occurrences of Mazama pocket gopher. There were no occurrences mapped within 600 feet of the site. 1 Thurston County. 2020. Site Inspection Protocol and Procedures. https://www.thurstoncountywa.gov/planning/planningdocuments/gopher-inspection-protocol-for-consultants-2020.pdf 2 U.S. Fish and Wildlife Service (USFWS). 2018. Letter regarding Guidance for Assessing Potential Take of Mazama Pocket Gophers in Thurston and Pierce Counties. USFWS, Washington Fish and Wildlife Office, Lacey, Washington. April 20, 2018. 3 Soil data for this assessment was obtained from Thurston Geodata web mapping application: https://map.co.thurston.wa.us/Html5Viewer/Index.html?viewer=Permitting.Main Mr. Emmanuel Mupinganjira September 20, 2020 CAPITAL LAND & WATER Page 3 Figure 1. Characteristic Grassy Area on Site. Figure 2. Characteristic Shrubby Area on Site. Survey Results The subject parcels were surveyed by USFWS-trained biologist, Erik Schwartz, Capital Land & Water Principal Ecologist. Capital Land and Water conducted one site inspection for mounds and other indicators of Mazama pocket gophers according to Thurston County’s Mazama pocket gopher review protocol over two days, August 18 and August 20, 2020. The biologist conducted a second survey on September 19, 2020. Mr. Emmanuel Mupinganjira September 20, 2020 CAPITAL LAND & WATER Page 4 The field survey conducted for this screening involved walking transects in a generally north/south direction throughout the study area, approximately 3 meters apart from each other. Some transects were interrupted by forested or brushy areas. Those areas were examined from the edges and by walking into the interior and then traversing around them. The survey was conducted to focus effort and provide good visual coverage of patchy grassy areas where activity would be most likely to occur. Surveys were conducted with moderately good visibility. Grass height was challenging in some areas, but areas of tall dense grass were patchy and extra effort was applied in those areas to ensure compete visual coverage. Several mounds, or remnants of old mounds, were observed. Each was carefully examined to determine if it showed indications of what species had created it. No mounds showed classic indicators of Mazama pocket gophers such as offset whole location, crescent or fan shaped soil deposits, sifted soil, “J” shaped entrances, or plugged entrances. Most appeared likely created by moles (centrally located holes) or simply showed signs of disturbance from a predator (Figure 3) and/or varying degrees of use by other types of wildlife that might include moles, voles, or rats. Exposed borrows and larger holes than would be associated with Mazama pocket gophers were the most encountered feature (Figure 4). If these apparently disturbed tunnels/entrances were actively used by gophers we would expect some instances of plugged holes. However, no plugs were observed. Of the mounds which were positively identifiable as either pocket gopher or mole mounds, all were indicative of mole activity, exhibiting classic characteristics of moles pushing dirt upward from the burrow into a conical mound with a “clumpy” texture (Figure 5). Figure 3. Ground Disturbance Likely Caused by Predator. Mr. Emmanuel Mupinganjira September 20, 2020 CAPITAL LAND & WATER Page 5 Figure 4. Example of Exposed Burrow. Figure 5. Example Mound Indicative of Mole Activity on Site. The second site inspection on September 19, 2020 occurred after several days of light, intermittent rain. Several fresh soil disturbances were observed on or near weathered, previously identified mounds. All were determined characteristic mole mounds. Numerous open burrows (holes and near surface tunnels with exposed sections) that were observed in the first inspection were observed still open and exposed during the second inspection. Those features were not indicative of pocket gopher activity since pocket gophers tend to plug holes of inhabited tunnels. No plugged holes were observed during either inspection. Also during the second inspection, the biologist observed wild rabbits; at least three individuals on two separate occasions. Mr. Emmanuel Mupinganjira September 20, 2020 CAPITAL LAND & WATER Page 6 Conclusions / Recommendations The subject parcel is mapped as containing a soil type that requires Mazama pocket gopher review by USFWS and local jurisdictions. However, the study area does not otherwise exhibit habitat characteristics that would be preferable to Mazama pocket gophers. Habitat is marginal. Suitability is limited in small patches and is unsuitable or marginally suitable in most areas throughout the study area. Signs that would potentially indicate pocket gopher presence such as classic gopher mound forms, plugged holes, and other characteristics were not observed anywhere within the study area during this screening. Conversely, features observed were indicative of moles and other burrowing and ground dwelling wildlife including rabbits. We have good confidence based on this survey that site characteristics are the result of current and past occupancy by moles and animals other than Mazama pocket gopher. Mazama pocket gopher occurrence within the study area is unlikely. Based on this assessment, Capital Land & Water recommends that future property development, such as commercial or industrial type buildings and their associated generally accepted land use consistent with local development and building codes, is not likely to adversely affect Mazama pocket gopher or to significantly alter Mazama pocket gopher habitat, including potential habitat. If you or agency reviewers have questions regarding the screening survey or this assessment, please contact me directly at (360) 790-5936 or email to: erik@caplandwater.com. Sincerely, Erik Schwartz, PWS Principal Ecologist CAPITAL LAND & WATER att: Survey #1 Map (Figure A-1) Survey #2 Map (Figure A-2) PHS Screen Capture (Figure A-3) Survey Forms (4p.) Soil Map (3p.) cc: CLW project file Figure A-1. Survey Path (Approximate), Survey #1, August 18-20, 2020. CAPITAL LAND AND WATER, LLC.CLW 2008-1310 9/20/2020 Mupinganjira MPG Survey #2 Parcels MPG Survey 9/19/20 100ft LEGEND Figure A-2. Survey #2, September 19, 2020. 64300800301 64300800302 CAPITAL LAND AND WATER, LLC.CLW 2008-1310 9/20/2020 Figure A-3. Washington Department of Fish and Wildlife Priority Habitat and Species Screen Capture (No MPG records within 1000 feet radius). CAPITAL LAND AND WATER, LLC.CLW 2008-1310 9/20/2020 Site Name and Parcel # Parcel #: _________________________________________________ Project #: ________________________________________________ Site/Landowner: __________________________________________ How were the data collected? (circle the method for each) Transect: Trimble Garmin Aerial Mounds Trimble Garmin Aerial Notes: ___________________________________________________ Field Team Personnel: (Indicate all staff present, CIRCLE who ﬁlled out form) Name: Name: Name: Others onsite (name/affiliaƟon) Site visit # (CIRCLE all that apply) 1st 2nd Unable to screen Notes: Do onsite condiƟons preclude the need for further visits? Yes No Dense woody cover that encompasses the enƟre site (trees/shrubs) that appears to preclude any potenƟal MPG use. Impervious Compacted Graveled Flooded Other ______________ Notes: Describe visibility for mound detecƟon: Poor Fair Good Notes: Request mowing? (CIRCLE and DESCRIBE WHERE MOWING IS NEEDED and SHOW ON AERIAL PHOTO Yes No N/A Notes: 2020 Thurston County Mazama Pocket Gopher Screening Field Form Site Visit Date: ______________ 64300800301-02 CLW # 2008-1310 1002 & 1102 Rhoton Rd. SE / OREAR GPS w/ ~1m accuracy and aerial used for positioning in field. E. Schwartz, Capital Land and Water Preliminary site visit: 8/12/2020 Survey start 8/18/2020 Survey complete 8/20/2020 8/18/2020 Some areas of dense woody cover. Some areas relatively poor visibility. Additional effort spent in those patches to ensure good visual coverage. Overall good confidence. SURVEY #1 CAPITAL LAND AND WATER, LLC.CLW 2008-1310 Mounds observed over the whole site are characterisƟc of: QuanƟfy or describe amount of each type and approx. # of mounds Group = 3 mounds or more No MPG mounds (circle) MPG mounds in GPS? (CIRCLE and DESCRIBE) If MPG mounds present, entered in GPS? None All Most Some Notes: Yes No N/A Does woody vegetaƟon onsite match aerial photo? Yes No - describe differences and show on parcel map/aerial: What porƟon(s) of the property was screened? (CIRCLE and DESCRIBE) All Part - describe and show on parcel map/aerial: Notes - Describe, and show on parcel map/aerial if applicable: Team reviewed and agreed to data recorded on form? (CIRCLE, and EXPLAIN if “No”) Yes No Reviewed by iniƟals: _____ _____ _____ _____ Notes: MPG Mounds Likely MPG Mounds Indeterminate Likely Mole Mounds Mole Mounds 0 0 0 30-40 5 Transects interrupted by some areas of forest/dense shrubs. See attached map. Reviewed photos and general observations with colleague to affirm judgment regarding some examples. Offsite review. Recommend at least one additional survey in approx. 30 days Best to occur after drought period ends. CAPITAL LAND AND WATER, LLC.CLW 2008-1310 Site Name and Parcel # Parcel #: _________________________________________________ Project #: ________________________________________________ Site/Landowner: __________________________________________ How were the data collected? (circle the method for each) Transect: Trimble Garmin Aerial Mounds Trimble Garmin Aerial Notes: ___________________________________________________ Field Team Personnel: (Indicate all staff present, CIRCLE who ﬁlled out form) Name: Name: Name: Others onsite (name/affiliaƟon) Site visit # (CIRCLE all that apply) 1st 2nd Unable to screen Notes: Do onsite condiƟons preclude the need for further visits? Yes No Dense woody cover that encompasses the enƟre site (trees/shrubs) that appears to preclude any potenƟal MPG use. Impervious Compacted Graveled Flooded Other ______________ Notes: Describe visibility for mound detecƟon: Poor Fair Good Notes: Request mowing? (CIRCLE and DESCRIBE WHERE MOWING IS NEEDED and SHOW ON AERIAL PHOTO Yes No N/A Notes: 2020 Thurston County Mazama Pocket Gopher Screening Field Form Site Visit Date: ______________ 64300800301-02 CLW # 2008-1310 1002 & 1102 Rhoton Rd. SE / OREAR GPS w/ ~1m accuracy and aerial used for positioning in field. No MPG mounds observed/recorded. E. Schwartz, Capital Land and Water 9/19/2020 Some areas of the site are covered by dense woody cover. Some areas relatively poor visibility. Additional effort spent in those patches to ensure good visual coverage. Overall good confidence. All grassy, non-shrub areas were inspected. SURVEY #2 Partial. See note. CAPITAL LAND AND WATER, LLC.CLW 2008-1310 Mounds observed over the whole site are characterisƟc of: QuanƟfy or describe amount of each type and approx. # of mounds Group = 3 mounds or more No MPG mounds (circle) MPG mounds in GPS? (CIRCLE and DESCRIBE) If MPG mounds present, entered in GPS? None All Most Some Notes: Yes No N/A Does woody vegetaƟon onsite match aerial photo? Yes No - describe differences and show on parcel map/aerial: What porƟon(s) of the property was screened? (CIRCLE and DESCRIBE) All Part - describe and show on parcel map/aerial: Notes - Describe, and show on parcel map/aerial if applicable: Team reviewed and agreed to data recorded on form? (CIRCLE, and EXPLAIN if “No”) Yes No Reviewed by iniƟals: _____ _____ _____ _____ Notes: MPG Mounds Likely MPG Mounds Indeterminate Likely Mole Mounds Mole Mounds 0 0 0 26 9 Transects interrupted by some areas of forest/dense shrubs. No MPG mounds. Several mole mounds were cataloged with waypoint and photos for file. solo inspection Pedestrian survey was focused in grassy areas with low or moderate woody shrub cover. Dense shrub areas that were not suitable habitat were precluded (generally not accessible and not traversed). Transects meandered around those areas. CAPITAL LAND AND WATER, LLC. CLW 2008-1310 Soil Map—Thurston County Area, Washington (1102 Rhoton Rd SE Vicinity) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/24/2020 Page 1 of 351996905199750519981051998705199930519999052000505199690519975051998105199870519993051999905200050530180530240530300530360530420530480530540530600530660530720 530180 530240 530300 530360 530420 530480 530540 530600 530660 530720 46° 57' 12'' N 122° 36' 13'' W46° 57' 12'' N122° 35' 45'' W46° 56' 59'' N 122° 36' 13'' W46° 56' 59'' N 122° 35' 45'' WN Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS84 0 100 200 400 600 Feet 0 35 70 140 210 Meters Map Scale: 1:2,640 if printed on A landscape (11" x 8.5") sheet. Soil Map may not be valid at this scale. MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Map Unit Polygons Soil Map Unit Lines Soil Map Unit Points Special Point Features Blowout Borrow Pit Clay Spot Closed Depression Gravel Pit Gravelly Spot Landfill Lava Flow Marsh or swamp Mine or Quarry Miscellaneous Water Perennial Water Rock Outcrop Saline Spot Sandy Spot Severely Eroded Spot Sinkhole Slide or Slip Sodic Spot Spoil Area Stony Spot Very Stony Spot Wet Spot Other Special Line Features Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Thurston County Area, Washington Survey Area Data: Version 14, Jun 4, 2020 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Mar 29, 2016—Oct 10, 2016 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Soil Map—Thurston County Area, Washington (1102 Rhoton Rd SE Vicinity) Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/24/2020 Page 2 of 3 Map Unit Legend Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 110 Spanaway gravelly sandy loam, 0 to 3 percent slopes 22.4 80.5% 111 Spanaway gravelly sandy loam, 3 to 15 percent slopes 5.4 19.5% Totals for Area of Interest 27.8 100.0% Soil Map—Thurston County Area, Washington 1102 Rhoton Rd SE Vicinity Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 8/24/2020 Page 3 of 3 22718430300 COWLES-PORTERFIELD, RUTH A PO BOX 525 YELM WA 98597 22719210700 THE OESER COMPANY PO BOX 156 BELLINGHAM WA 98227 57630100000 KINGSVIEW DIV 3 HOMEOWNERS ASSN PO BOX 2506 KIRKLAND WA 98083 57630100100 ABBOTT, RICKY & ELIZABETH J 15946 QUAIL MEADOWS CT SE YELM WA 98597 57630100200 SMITH, HOLLY A 15942 QUAIL MEADOWS CT SE YELM WA 98597 57630100300 REE, ANTHONY H & KIMBERLEE K 15938 QUAIL MEADOWS CT SE YELM WA 98597 57630100400 NEMETH, MATTHEW & JAMIE S 15934 QUAIL MEADOWS CT SE YELM WA 98597 57630100500 THORNTION, DENNIS W & LISA M 15930 QUAIL MEADOWS CT SE YELM WA 98597 57630101600 REE, ANTHONY W 15929 QUAIL MEADOWS CT SE YELM WA 98597 57630101700 WINCHELL, JAHKEITH & COURTNEY 15933 QUAIL MEADOWS CT SE YELM WA 98597 57630101800 MICHELS, JOSEPH & MICHELLE 15937 QUAIL MEADOWS CT SE YELM WA 98597 57630101900 FISCHER, JORDAN A 15941 QUAIL MEADOWS CT SE YELM WA 98597 57630102000 SLAPE, INEZ D 15945 QUAIL MEADOWS CT SE YELM WA 98597 57660003700 SHIPPENTOWER, EDMOND L 1107 RHOTON CT YELM WA 98597 57660003800 BRADLEY, WILLIAM E 1106 RHOTON CT NW YELM WA 98597 57660003900 PFLUGMACHER, LINDA 1105 NW RHOTON CT YELM WA 98597 57660004000 ANDERSON, KARL W & CHRISTINE I 1104 RHOTON CT NW YELM WA 98597-9750 57660004100 BERLIN, JENNIFER 1119 RHOTON CT NW YELM WA 98597 57660004200 JANSEN, CHRIS J & NANCY M 754 111TH ST S TACOMA WA 98444-5620 57660004300 ZATKOVICH, CINDY A 1117 RHOTON CT NW YELM WA 98597 64300800301 MODERN RESOURCES LLC 4810 RACCOON VALLEY RD SE OLYMPIA WA 98513 64300800302 MODERN RESOURCES LLC 4810 RACCOON VALLEY RD SE OLYMPIA WA 98513 64300800303 OREAR, CANDY 730 SW INDUSTRIAL WAY BEND OR 97702 64300900400 YELM, CITY OF 106 2ND ST SE YELM WA 98597-7667 ABBOTT, RICKY & ELIZABETH J 15946 QUAIL MEADOWS CT SE YELM, WA 98597 ANDERSON, KARL W & CHRISTINE I 1104 RHOTON CT NW YELM, WA 98597-9750 BERLIN, JENNIFER 1119 RHOTON CT NW YELM, WA 98597 BRADLEY, WILLIAM E 1106 RHOTON CT NW YELM, WA 98597 COWLES-PORTERFIELD, RUTH A PO BOX 525 YELM, WA 98597 FISCHER, JORDAN A 15941 QUAIL MEADOWS CT SE YELM, WA 98597 JANSEN, CHRIS J & NANCY M 754 111TH ST S TACOMA, WA 98444-5620 KINGSVIEW DIV 3 HOMEOWNERS ASSN PO BOX 2506 KIRKLAND, WA 98083 MICHELS, JOSEPH & MICHELLE 15937 QUAIL MEADOWS CT SE YELM, WA 98597 MODERN RESOURCES LLC 4810 RACCOON VALLEY RD SE OLYMPIA, WA 98513 NEMETH, MATTHEW & JAMIE S 15934 QUAIL MEADOWS CT SE YELM, WA 98597 OREAR, CANDY 730 SW INDUSTRIAL WAY BEND, OR 97702 PFLUGMACHER, LINDA 1105 NW RHOTON CT YELM, WA 98597 REE, ANTHONY H & KIMBERLEE K 15938 QUAIL MEADOWS CT SE YELM, WA 98597 REE, ANTHONY W 15929 QUAIL MEADOWS CT SE YELM, WA 98597 SHIPPENTOWER, EDMOND L 1107 RHOTON CT YELM, WA 98597 SLAPE, INEZ D 15945 QUAIL MEADOWS CT SE YELM, WA 98597 SMITH, HOLLY A 15942 QUAIL MEADOWS CT SE YELM, WA 98597 THE OESER COMPANY PO BOX 156 BELLINGHAM, WA 98227 THORNTION, DENNIS W & LISA M 15930 QUAIL MEADOWS CT SE YELM, WA 98597 WINCHELL, JAHKEITH & COURTNEY 15933 QUAIL MEADOWS CT SE YELM, WA 98597 YELM, CITY OF 106 2ND ST SE YELM, WA 98597-7667 ZATKOVICH, CINDY A 1117 RHOTON CT NW YELM, WA 98597 105 Yelm Ave W (360) 458-3835 Yelm, WA 98597 (360) 458-3144 FAX www.ci.yelm.wa.us City of Yelm Community Development Department ENVIRONMENTAL CHECKLIST Fee Date Received By File No. Instructions: The State Environmental Policy Act (SEPA) requires all governmental agencies to consider the environmental impacts of a proposal before making decisions. The purpose of this checklist is to provide information to help identify impacts from your proposal, to reduce or avoid impacts from the proposal if it can be done, and to help the City decide whether an EIS is required. An environmental impact statement (EIS) must be prepared for any proposal with probable significant adverse impacts on environmental quality. This environmental checklist asks you to describe some basic information about your proposal. The City will use this checklist to determine whether the environmental impacts of your proposal are significant and require preparation of an EIS. You must answer each question accurately, carefully and to the best of your knowledge. Answer the questions briefly, but give the best description you can. In most cases, you should be able to answer the questions from your own observations or project plans without the need for experts. If you do not know the answer, or if a question does not apply to your proposal, write "do not know" or "does not apply". Complete answers to the questions now may avoid delays later. If the space provided is too small, feel free to attach additional sheets. Some questions ask about governmental regulations, such as zoning, shoreline, and landmark designations. Answer these questions if you can. If you have problems, the city staff can assist you. The checklist questions apply to all parts of your proposal even if you plan to do them over a period of time or on different parcels of land. Attach any additional information that will help describe your proposal or its environmental effects. You may be asked to explain your answers or provide additional information for determining if there may be significant adverse impacts. Nonproject Proposals Only: Complete both the checklist (even though many questions may be answered "does not apply") and the Supplemental Sheet for Nonproject Actions (part D). For nonproject actions, the references in the checklist to the words "project," "applicant," and "property or site" should be read as "proposal," "proposer," and "affected geographic area," respectively. City of Yelm Environmental Checklist Page 1 CITY OF YELM CITY USE ONLY FEE: $150.00 ENVIRONMENTAL CHECKLIST DATE REC'D BY: FILE NO. A. BACKGROUND 1. Name of proposed project, if any: 2. Name of applicant: 3. Address, phone number and email address of applicant and of any other contact person: 4. Date checklist prepared: 5. Agency requesting checklist: 6. Proposed timing or schedule (including phasing, if applicable): 7. Do you have any plans for future additions, expansion, or further activity related to or connected with this proposal? If yes, explain. 8. List any environmental information you know about that has been prepared, or will be prepared, directly related to this proposal. 9. Do you know whether applications are pending for governmental approvals of other proposals directly affecting the property covered by your proposal? If yes, explain. 10. List any government approvals or permits that will be needed for your proposal, if known. City of Yelm Planning Dept December 2020-July 2021, Site Civil Phase I, Phase II Metal Building Structure NO Site drainage and grading plans, See Skillings Design 2020, Gopher Screening, See Capital Land and Water 2020 Report NO City of Yelm frontage improvements deferral, See project Per-submissions notes-Transportation City of Yelm Environmental Checklist Page 2 11. Give brief, complete description of your proposal, including the proposed uses and the size of the project and site. There are several questions later in this checklist that ask you to describe certain aspects of your proposal. You do not need to repeat those answers on this page. 12. Location of the proposal. Give sufficient information for a person to understand the precise location of your proposed project, including a street address, if any, and section, township, and range, if known. If a proposal would occur over a range of area, provide the range or boundaries of the site(s). Provide a legal description, site plan, vicinity map, and topographic map, if reasonably available. You need not duplicate maps or detailed plans submitted with any permit applications related to this checklist. B. ENVIRONMENTAL ELEMENTS 1. Earth a. General description of the site (circle one): flat, rolling, hilly, steep slopes, mountainous, other b. What is the steepest slope on the site (approximate percent slope)? c. What general types of soils are found on the site (for example, clay, sand, gravel, peat, muck)? If you know the classification of agricultural soils, specify them and note any prime farmland. d. Are there surface indications or history of unstable soils in the immediate vicinity? If so, describe. e. Describe the purpose, type, and approximate quantities of any filling or grading proposed. Indicate source of fill. f. Could erosion occur as a result of clearing, construction, or use? If so, generally describe. Developing the two lots into a 20,000sf millwork/casework manufacturing facility Situated in The City of Yelm, in Thurston County Washington 1002 NW Rhoton Road Yelm WA 98597 3% The soil types comprise of Spanaway gravelly sandy loam NO Native cut and fill, balanced site approximately 800 cubic yards Structural fill, import 1200 cubic yards Yes City of Yelm Environmental Checklist Page 3 g. About what percent of the site will be covered with impervious surfaces after project construction such as asphalt or buildings? h. Proposed measures to reduce or control erosion, or other impacts to the earth, if any: 2. Air a. What types of emissions to the air would result from the proposal (i.e., dust, automobile exhaust, odors, industrial wood smoke) during construction and when the project is completed? If any, generally describe and give approximate quantities if known. b. Are there any off-site sources of emissions or odor that may affect your proposal? If so, generally describe. c. Proposed measures to reduce or control emissions or other impacts to air, if any: 3. Water a. Surface Water 1) Is there any surface water body or wetland on or in the immediate vicinity of the site (including year-round and seasonal streams, saltwater, lakes, ponds)? If yes, describe type and provide names. State what stream or river it flows into? 2) Will the project require any work over, in, or adjacent to (within 300 feet) the described waters? If yes, please describe and attach available plans. 3) Estimate the amount of fill and dredge material that would be placed in or removed from surface water or wetlands and indicate the area of the site that would be affected. Indicate the source of fill material. 4) Will the proposal require surface water withdrawals or diversions? Give general description, purpose, and approximate quantities if known. 35% Infiltration ponds, BMPs per Washington State Storm Water Manual Fugitive construction dust resulting from earthwork. Delivery vehicles exhaust NO BMPs per Washington State Storm Water Manual NO NO NA NO City of Yelm Environmental Checklist Page 4 5) Does the proposal lie within a 100-year floodplain? If so, note elevation on the site plan. 6) Does the proposal involve any discharges of waste materials to surface waters? If so, describe the type of waste and anticipated volume of discharge. b. Groundwater: 1) Will groundwater be withdrawn, or will water be discharged to groundwater? Give general description, purpose, and approximate quantities if known. 2) Describe the underlying aquifer with regard to quality and quantity, sensitivity, protection, recharge areas, etc. 3) Describe waste material that will be discharged into or onto the ground from septic tanks or other sources, if any (such as domestic sewage; industrial byproducts; agricultural chemicals). c. Water Runoff (including storm water): 1) Describe the source of runoff (including storm water) and method of collection and disposal, if any (include quantities, if known). Where will this water flow? Will this water flow into other waters? If so, describe. 2) Could waste materials enter ground or surface waters? If so, generally describe. d. Proposed measures to reduce or control surface, ground, and runoff water impacts, if any: NO NO Infiltration ponds will be used during construction and permanent storm water management The project is located within the Yelm aquifer with ground water levels ranging in depth from 290 to 300ft. These levels fluctuate with the Nisqually river. No discharge expected beyond the surface storm water All surface storm water from roof line and urban surfaces will be directed and collected in permanently constructed bioswells Very low potential for waste materials to enter the ground or surface water NA City of Yelm Environmental Checklist Page 5 4. Plants a. Check or circle types of vegetation found on the site: ____ deciduous tree: alder, maple, oak, aspen, other ____ evergreen tree: fir, cedar, pine, other ____ shrubs ____ grasses ____ pasture ____ crops or grains ____ wet soil plants: cattail, buttercup, bulrush, skunk cabbage, other ____ water plants: water lily, eelgrass, milfoil, other ____ other types of vegetation b. What kind and amount of vegetation will be removed or altered? c. List threatened or endangered species known to be on or near the site. d. Proposed landscaping, use of native plants, or other measures to preserve or enhance vegetation on the site, if any: 5. Animals a. Circle any birds and animals that have been observed on or near the site or are known to be on or near the site: birds: hawk, heron, ducks, eagle, songbirds, other: mammals: deer, bear, elk, beaver, other: fish: bass, salmon, trout, shellfish, other: b. List any priority, threatened or endangered species known to be on or near the site. c. Is the site part of a migration route? If so, explain. d. Proposed measures to preserve or enhance wildlife, if any: 6. Energy and Natural Resources a. What kinds of energy (electric, natural gas, gasoline, heating oil, wood, solar etc.) will be used to meet the completed project's energy needs? Describe whether it will be used for heating, manufacturing, transportation, etc. All existing shrubs and grasses withing construction limits, trees within the building footprints and parking lot will be removed None None None None None None No None City of Yelm Environmental Checklist Page 6 b. Would your project affect the potential use of solar energy by adjacent properties? If so, generally describe. c. What kinds of energy conservation features are included in the plans of this proposal? List other proposed measures to reduce or control energy impacts, if any: 7. Environmental Health a. Are there any environmental health hazards, including exposure to toxic chemicals, risk of fire and explosion, spills, of hazardous waste, that could occur as a result of this proposal? If so, describe. 1) Describe special emergency services that might be required. 2) Proposed measures to reduce or control environmental health hazards, if any: b. Noise 1) What types of noise exist in the area which may affect your project (for example: traffic, equipment operation, other)? 2) What types and levels of noise would be created by or associated with the project on a short-term or a long-term basis (for example: traffic, construction, operation, other)? Indicate what hours noise would come from the site. 3) Proposed measures to reduce or control noise impacts, if any: 8. Land and Shoreline Use a. What is the current use of the site and adjacent properties? b. Has the site been used for mineral excavation, agriculture or forestry? If so, describe. No None No No None None Construction equipment and activities 7am to 6pm Monday through Saturday None Vacant None City of Yelm Environmental Checklist Page 7 c. Describe any structures on the site. d. Will any structures be demolished? If so, what? e. What is the current comprehensive plan designation of the site? f. What is the current zoning classification of the site? g. If applicable, what is the current shoreline master program designation of the site? h. Has any part of the site been classified as a "natural resource", "critical" or "environmentally sensitive" area? If so, specify. i. Approximately how many people would reside or work in the completed project? j. Approximately how many people would the completed project displace? k. Proposed measures to avoid or reduce displacement impacts, if any: l. Proposed measures to ensure the proposal is compatible with existing and projected land uses and plans, if any: 9. Housing a. Approximately how many units would be provided, if any? Indicate whether high, middle, or low-income housing. b. Approximately how many units, if any, would be eliminated? Indicate whether high, middle, or low-income housing. None No Industrial Zoning Industrial Zoning NA No 13 0 NA NA 0 0 City of Yelm Environmental Checklist Page 8 c. Proposed measures to reduce or control housing impacts, if any: 10. Aesthetics a. What is the tallest height of any proposed structure(s), not including antennas; what is the principal exterior building material(s) proposed? b. What views in the immediate vicinity would be altered or obstructed? c. Proposed measures to reduce or control aesthetic impacts, if any: 11. Light and Glare a. What type of light or glare will the proposal produce? What time of day would it mainly occur? b. Could light or glare from the finished project be a safety hazard or interfere with views? c. What existing off-site sources of light or glare may affect your proposal? d. Proposed measures to reduce or control light and glare impacts, if any: 12. Recreation a. What designated and informal recreational opportunities are in the immediate vicinity? b. Would the proposed project displace any existing recreational uses? If so, describe. c. Proposed measures to reduce or control impacts or provide recreation opportunities: NA 24ft Metal Siding None NA Parking lot and security lights No None None None None None City of Yelm Environmental Checklist Page 9 13. Historic and Cultural Preservation a. Are there any places or objects listed on, or proposed for, national, state, or local preservation registers known to be on or next to the site? If so, generally describe. b. Generally describe any landmarks or evidence of historic, archeological, scientific, or cultural importance known to be on or next to the site. c. Proposed measures to reduce or control impacts, if any: 14. Transportation a. Identify sidewalks, trails, public streets and highways serving the site, and describe proposed access to the existing street system. Show on site plans, if any. b. Is site currently served by public transit? By what means? If not, what plans exist for transit service? c. How many parking spaces would the completed project have? How many would the project eliminate? d. Will the proposal require any new sidewalks, trails, roads or streets, or improvements to existing sidewalks, trails, roads or streets, not including driveways? If so, generally describe (indicate whether public or private). e. Will the project use (or occur in the immediate vicinity of) water, rail, or air transportation? If so, generally describe. f. How many vehicular trips per day would be generated by the completed project? If known, indicate when peak volumes would occur. g. Proposed measures to reduce or control transportation impacts, if any: None None NA Rhoton Road No 14 new and 0 eliminated Not at this time. The property owner is requesting all road and street improvements are deferred No 15 trips Employee carpooling will be encouraged City of Yelm Environmental Checklist Page 10 15. Public Services a. Would the project result in an increased need for public services (for example: fire protection, police protection, health care, schools, other)? If so, generally describe: b. Proposed measures to reduce or control direct impacts on public services, if any. 16. Utilities a. Circle utilities currently available at the site: electricity, natural gas, water, refuse service, telephone, sanitary sewer, septic system, other. b. Describe the utilities that are proposed for the project, the utility providing the service, and the general construction activities on the site or in the immediate vicinity which might be needed. C. SIGNATURE The above answers are true and complete to the best of my knowledge. I understand that the City of Yelm is relying on them to make its decision. Signature: Date Submitted: Fire and Emergency services Industrial Safety Plans All of the above City of Yelm, Puget Sound Energy, Comcast and LeMay 12/07/2020 City of Yelm Environmental Checklist Page 11 SUPPLEMENTAL ENVIRONMENTAL CHECKLIST FOR NONPROJECT ACTIONS (Do not use this sheet for project actions.) When answering these questions, be aware of the extent of the proposal, or the types of activities likely to result from the proposal, would affect the item at a greater intensity or at a faster rate than if the proposal were not implemented. Respond briefly and in general terms. 1. How would the proposal be likely to increase discharge to water; emissions to air; production, storage, or release of toxic or hazardous substances; or production of noise? Proposed measures to avoid or reduce such increases are: 2. How would the proposal be likely to affect plants, animals, fish, or marine life? Proposed measures to protect or conserve plants, animals, fish, or marine life are: 3. How would the proposal be likely to deplete energy or natural resources? Proposed measures to protect or conserve energy and natural resources are: 4. How would the proposal be likely to use or affect critical or environmentally sensitive areas or areas designated (or eligible or under study) for governmental protection, such as parks, wilderness, wild and scenic rivers, threatened or endangered species habitat, historic or cultural sites, wetlands, floodplains, or natural resource areas? Proposed measures to protect such resources or to avoid or reduce impacts are: Increase in vehicle traffic( emission and noise) Carpooling and day time deliveries Low probability Tree line protection of the remaining trees and install and maintain landscaping Very low. All resources provided by public utilities Does not apply City of Yelm Environmental Checklist Page 12 5. How would the proposal be likely to affect land and shoreline use, including whether it would allow or encourage land or shoreline uses incompatible with existing plans? Proposed measures to avoid or reduce shoreline and land use impacts are: 6. How would the proposal be likely to increase demands on transportation or public services and utilities? Proposed measures to reduce or respond to such demand(s) are: 7. Identify, if possible, whether the proposal may conflict with local, state, or federal laws or requirements for the protection of the environment. Does not apply Minimum impact Industrial Safety plan and employee carpool I do not know DRAINAGE REPORT PRELIMINARY MODERN RESOURCES LLC SITE DEVELOPMENT SC Project #20136 DECEMBER 2020 CITY OF YELM 1002 & 1102 Rhoton Road Southeast Yelm, WA 98597 Prepared By: Project Engineer: Ian Y. Lee, P.E. Skillings, Inc. Phone: (360) 491-3399 Email: ilee@skillings.com Applicant: Emmanuel Mupinganjira Modern Resources LLC Phone: (360) 890-7286 Email: emmanuelm@moderncw.com Skillings, Inc. Modern Resources LLC Site Development SC# 20136 2 Drainage Report ENGINEER'S CERTIFICATE FOR THE MODERN RESOURCES LLC SITE DEVELOPMENT I hereby state that this Drainage Control Plan for Modern Resources LLC Site Development has been prepared by me or under my supervision and meets the standard of care and expertise which is usual and customary in this community for professional engineers. I understand that Yelm does not and will not assume liability for the sufficiency, suitability, or performance of drainage facilities prepared by me. Prepared By: _________________________________________ _____________________ Ian Y. Lee, P.E. Date SKILLINGS, INC Skillings, Inc. Modern Resources LLC Site Development SC# 20136 3 Drainage Report TABLE OF CONTENTS Section Page 1 Proposed Project Description ................................................................................ 4 2 Existing Conditions Description ............................................................................. 5 3 Proposed Improvements Description .................................................................... 6 4 Minimum Requirements ........................................................................................ 7 ATTACHMENTS A. Flow Chart for Determining Requirements for New Development B. FEMA Base Flood Elevation Map C. Existing Conditions Map D. Proposed Conditions Map E. Construction Stormwater Pollution Prevention Plan (CSWPPP) F. Source Control BMPs G. Flow Chart for Determining MR #5 Requirements H. WWHM 2012 Results I. USDA Natural Resources Conservation Service Geotechnical Web Soil Survey J. Site Plan, TESC and Drainage Plans K. Onsite Stormwater Management BMPs L. Runoff Treatment BMPs M. Flow Control BMPs Skillings, Inc. Modern Resources LLC Site Development SC# 20136 4 Drainage Report SECTION 1 Proposed Project Description This Drainage Plan has been completed in accordance with the Department of Ecology’s 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW). Per Figure I-3.1 of Section I-3.3, Volume I of the 2019 SWMMWW, this proposed project is classified as New Development. The proposed project will have 64,665 square feet (1.48 acres) of new hard surface area and a total of 70,350 square feet (1.62 acres) of disturbed land area. Per Figure I-3.1 of Section I-3.3, Volume I of the 2019 SWMMWW, all Minimum Requirements will apply to the new hard surfaces and the converted vegetation areas. Figure I-3.1 is included as Attachment A. The project consists of constructing a cabinet manufacturing facility, asphalt pavement parking lot, driveway, and offloading zone area, water and sewer utilities, stormwater infiltration and bioretention facilities, landscaped areas, and gravel building perimeter on existing undeveloped land in Yelm, Washington (Thurston County Tax Parcels 64300800301 and 64300800302). Skillings, Inc. Modern Resources LLC Site Development SC# 20136 5 Drainage Report SECTION 2 Existing Conditions Description Parcels #64300800301 and #64300800302 are located at 1102 & 1002 Rhoton Road Southeast in Yelm, Washington, representing 2.07 acres and 2.78 acres of undeveloped land, respectively. The eastern half of the site consists of moderate slopes (3% to 11%) that gently fall from east to west and flattening out in the western half of both tax parcels (Less than 3%). Native Fir trees ranging between 11- and 48- inches diameter populate in a row along the northern boundary of parcel #64300800301, with the majority occupying the eastern-central portion of the parcel in clusters where the proposed development is to be located. Other native vegetation covers the remainder of the site. The Site Plan showing existing conditions is included as Attachment C. Federal Emergency Management Agency Flood Insurance Rate Maps indicate a small portion of the southwest corner of parcel #64300800302 is located within the 100-year floodplain of Yelm Creek. This is outside the proposed development for this current project. The FEMA FIS inundation boundary is included as Attachment B. Additionally, the proposed development will incorporate stormwater treatment according to the 2019 SWMMWW, as the City of Yelm is considered to be within a critical aquifer recharge area. On site soil conditions indicate suitable habitat for the Mazama Pocket Gopher, a protected species on the Washington Priority Species and Habitat List as well as the Federal Threatened Species List. It is our understanding that the Owner and the City of Yelm previously completed a Critical Areas Report and found no evidence of pocket gopher activity. Skillings, Inc. Modern Resources LLC Site Development SC# 20136 6 Drainage Report SECTION 3 Proposed Improvements The undeveloped property is to be developed, with the construction of a cabinet manufacturing facility, asphalt pavement parking lot, driveway, and offloading zone area, water and sewer utilities, stormwater infiltration and bioretention facilities, landscaped areas, and gravel building perimeter on existing undeveloped land in Yelm, WA (Thurston County Tax Parcels 64300800301 and 64300800302). The proposed project will disturb approximately 70,350 square feet (1.62 acres) and add approximately 64,665 square feet (1.48 acres) of new hard surface area. The proposed new hard surface area consists of asphalt pavement, gravel, and proposed shop building footprint, while the total disturbed area consists of all new hard surfaces and landscaped areas. The proposed shop building, and associated development, will be mostly located on parcel #64300800301. All stormwater collected from the rooftop of the new 20,000 square foot development will be routed, along with stormwater collected from gravel and moderate slope forested areas into 17,000 square feet of infiltration galleries on site. The remainder of the runoff from pollution generating surfaces, including the asphalt pavement and gravel, will be treated within the 662.5 square-foot Bioretention Facility on site. All collection, treatment, and infiltration requirements will be in conformance with the 2019 SWMMWW. Additionally, the proposed development will require the removal of several trees. Therefore, this project will replace every tree removed (8” diameter, 4.5’ tall), per the City of Yelm Muncipal Code Section 18.57.090C. These trees will be replanted within a 10’ vegetative parcel setback boundary around parcel #64300800301. The Proposed Improvements Map showing surface coverage is included as Attachment D. Surface Coverage Table Square Feet % of Total Total Project Area (Parcel #64300800301 & #64300800302) 211,380 100 Existing Hard Surfaces 0 0 Replaced Hard Surfaces 0 0 Removed Hard Surfaces 0 0 New Hard Surfaces (Building, Pavement, Gravel, and Wall) 64,665 30.6 Disturbed Area (includes everything within the limits of disturbance, Attachment C) 70,350 33.3 Total Hard Surfaces After Project 64,665 30.6 Skillings, Inc. Modern Resources LLC Site Development SC# 20136 7 Drainage Report Section 4 Minimum Requirements: This project must address All Minimum Requirements. The requirements will apply to the new hard surfaces (pavement, gravel, and rooftop) and the converted vegetation areas (landscaped areas). Minimum Requirement #1 – Preparation of Stormwater Site Plans This Drainage Plan has been prepared for City of Yelm review. Minimum Requirement #2 - Construction Stormwater Pollution Prevention Plan A Construction SWPPP has been prepared for this project and is included as Attachment E. Minimum Requirement #3 – Source Control of Pollution Source Control BMPs prevent stormwater from coming in contact with pollutants and are a cost- effective means of reducing pollutants in stormwater. The following source control BMPs, in accordance with Volume IV of the 2019 SWMMWW, were identified for this proposed commercial development project. All applicable BMPs are mandatory and must be implemented at the site. • S408 BMPs for Dust Control at Manufacturing Areas • S411 Landscaping and Lawn/Vegetation Management • S417 Maintenance of Stormwater Drainage and Treatment Systems • S421 Parking and Storage of Vehicle and Equipment • S424 Roof/Building Drains at Manufacturing and Commercial Buildings • S442 Labeling Storm Drain Inlets on your Property • S447 Roof Vents • S450 Irrigation • S453 Formation of a Pollution Prevention Team • S454 BMPs for Preventative Maintenance / Good Housekeeping • S455 Spill Prevention and Cleanup • S456 Employee Training • S457 Inspections • S458 Record Keeping Source Control BMPs are included in Attachment F. Minimum Requirement #4 – Preservation of Natural Drainage Systems and Outfalls No changes to the existing drainage patterns are anticipated. The proposed improvements will not change the existing flow directions or discharge points of the site. Minimum Requirement #5 – Onsite Stormwater Management Based on Figure I-3.3 of Section I-3.4.5, Volume I of the 2019 SWMMWW, the project will meet LID Performance Standard through the use of any Flow Control BMP(s) and apply BMP T5.13 Post Construction Soil Quality and Depth for all landscaped areas. Figure I-3.3 is included as Attachment G. Skillings, Inc. Modern Resources LLC Site Development SC# 20136 8 Drainage Report BMP T7.30 Bioretention will be utilized to manage the volume of runoff generated from the asphalt pavement. The remainder of the runoff generated by the proposed building, gravel perimeter, and surrounding contributing moderate forest areas, will be managed by the approximately 17,000 square feet of underground infiltration galleries, BMP T7.20 Infiltration Trenches. All proposed onsite stormwater generated from new hard and disturbed surfaces withing parcels #64300800301 and #64300800302 will be managed within parcel #64300800301. Onsite Stormwater Management BMPs are included as Attachment K. The continuous runoff model, Western Washington Hydrologic Model version 2012 (WWHM 2012) was utilized to size the volume of the proposed Bioretention and Infiltration Gallery facilities. Basins contributing runoff to these proposed facilities are included within the Proposed Conditions as Attachment D. The results of WWHM 2012 are included as Attachment H. Supplemental guidelines in the 2019 SWMMWW suggest that due to the gross level application of continuous runoff modeling and assumptions concerning minimum flows needed to maintain uses, watersheds must retain the majority of their natural vegetation cover and soils, and developments must minimize their disruption of the natural hydrologic cycle in order to avoid significant degradation of natural resources. Therefore, BMP T5.40 Preserving Native Vegetation shall be utilized to preserve as much of the existing vegetation and trees as feasible for the proposed development. One tree shall be planted within the project area for every tree removed during this process per City of Yelm Municipal Code. Typically, design infiltration of the native soil is a combination of measured saturated hydraulic conductivity and correct factors found in Table V-5.1 of the 2019 SWMMWW. In the absence of geotechnical investigation, the USDA Natural Resources Conservation Service (NRCS) web soil survey was utilized to determine a suitable range of initial infiltration rates (1.98 – 5.95 inches per hour). A conservative design infiltration rate of 1 inch per hour was chosen for the Bioretention and Infiltration Gallery model in 2012 WWHM, including the 2019 SWMMWW recommended infiltration safety factor of 4. The NRC web soil survey results utilized for sizing infiltration and treatment through native soils on site are included as Attachment I. The Site Plan, TESC and Drainage Plans are all included as Attachment J. Minimum Requirement #6 – Runoff Treatment This project shall provide treatment of all stormwater generated from pollutant generated new hard surfaces. These surfaces include the proposed asphalt pavement, and all surfaces the contribute flow to this surface, including gravel and moderate forest areas. The Runoff Treatment BMP shall be BMP T7.30 Bioretention. This proposed new facility was sized for 91% minimum water quality treatment utilizing the 2012 WWHM Continuous Simulation Method. The model results show that the 103’ x 9.4’ (960 SF Bottom Area) Bioretention facility, with 3:1 side slopes and three soil layers consisting of 0.25’ of ASTM 100, 1.5’ of Bioretention Soil Mix, and 3’ of Gravel, will be sufficient to treat 98.86 percent of all runoff generated from pollution generating new hard surfaces. The remainder the water will be infiltrated through the 12-inch diameter, 1.5’ high overflow structure within the facility. The WWHM report and results are included as Attachment H. The proposed Bioretention Facility for water quality treatment can be located within the Site Plan, TESC and Drainage Plans that are included as Attachment J. Skillings, Inc. Modern Resources LLC Site Development SC# 20136 9 Drainage Report No stormwater treatment BMPs shall be built within the natural vegetated buffer defined by the site plan. The following Runoff Treament BMPs, in accordance with Volume V Chapter 5 of the 2019 SWMMWW, were identified for this proposed commercial development project. Runoff Treatment BMPs are included as Attachment L. • BMP T7.30 Bioretention Minimum Requirement #7 – Flow Control This project shall apply Flow Control BMPs in accordance with the following requirements to reduce impacts of stormwater runoff from hard surfaces and land cover conversions. There are no TDA’s exempt from this requirement on this site. All stormwater runoff generated from the proposed asphalt pavement, gravel, and rooftop surfaces that are not otherwise infiltrated through the proposed Bioretention Facility’s Bioretention Soil Mix (BSM), must be infiltered by other means through the native onsite soils. BMP T7.20 Infiltration Trenches shall be utilized to infiltrate all the runoff generated by converted land area and hard surfaces unable to infiltrate by means of BMP T7.30 Bioretention. This includes all runoff that passes through the overflow structure of the BMP T7.30 Bioretention. The total area of proposed BMP T7.20 Infiltration Trenches shall be approximately 17,000 square feet of infiltration area, in accordance with the 2012 WWHM results of Attachment H. The following Flow Control BMPs, in accordance with Volume V Chapter 5 of the 2019 SWMMWW, were identified for this proposed commercial development project. Flow Control BMPs are included as Attachment M. • BMP T7.30 Bioretention • BMP T7.20 Infiltration Trenches Minimum Requirement #8 – Wetland Protection The project will not discharge runoff into a wetland, either directly or indirectly through a conveyance system. All runoff will be infiltrated on-site. Minimum Requirement #9 – Operation and Maintenance An operation and maintenance schedule shall be provided for all proposed stormwater facilities and BMPs, and the party (or parties) responsible for maintenance and operation shall be identified. ATTACHMENT A Flow Chart for Determining Requirements for New Development Figure 1-3.1: Flow Chart for Determining Requirements for New Development Stam Here See Redevelopment Project Does the Site have 35% Yes Thresholds and the Figure "Flow or more of existing hard Chart for Determining surface coverage? Requirements for Redevelopment". No �� Does the Project convert % acres or more of vegetation to Does the Project result in lawn or landscaped areas, or 5,000 square feet, or No convert 2.5 acres or more of greater, of new plus native vegetation to pasture? replaced hard surface Yes JINC area? I -- -- \ No Yes �� Does the Project result in 2,000 square feet, or greater, of new plus All Minimum Requirements replaced hard surface area? apply to the new and replaced hard surfaces and converted Yes JINC vegetation areas. Does the Project have land Minimum Requirements #1 disturbing activities of 7,000 through #5 apply to the new Yes square feet or greater? and replaced hard surfaces and the land disturbed. No Minimum Requirement #2 applies. Flaw Chart for Determining Requirements for New Development DEPARTMENT O F Revised March 2019 ECOLOGYPlease see tMp.1/wsvw.ecy.wa.govlcDpyright.htmI for copyright notice including permissions. State of Washington limitation of liability, and disdaimer- 2019 Stormwater Management Manual for Western Washington Volume 1- Chapter 3 - Page 89 ATTACHMENT B FEMA Base Flood Elevation Map The information included on this map has been compiled by Thurston County staff from a variety of sources and is subject to change without notice. Additional elements may be present in reality that are not represented on the map. Ortho-photos and other data may not align. The boundaries depicted by these datasets are approximate. This document is not intended for use as a survey product. ALL DATA IS EXPRESSLY PROVIDED ‘AS IS’ AND ‘WITH ALL FAULTS’. Thurston County makes no representations or warranties, express or implied, as to accuracy, completeness, timeliness, or rights to the use of such information. In no event shall Thurston County be liable for direct, indirect, incidental, consequential, special, or tort damages of any kind, including, but not limited to, lost revenues or lost profits, real or anticipated, resulting from the use, misuse or reliance of the information contained on this map. If any portion of this map or disclaimer is missing or altered, Thurston County removes itself from all responsibility from the map and the data contained within. The burden for determining fitness for use lies entirely with the user and the user is solely responsible for understanding the accuracy limitation of the information contained in this map. Authorized for 3rd Party reproduction for personal use only. FEMA Flood Map 10,738Scale 1: 0 12/21/2020 Note: 500yr and 100yr Legend 500 1000 Feet Published: Map Created Using GeoData Public Website Flood Zones FEMA 100 Year (1%) 500 Year (0.2%) Parcel Boundaries Roads - Major (Large Scale) <all other values> I 5 ACCESS; US 101 ACCESS; US 101 SB OFF RAMP I 5; US 101 Roads (Large Scale) Railroads County Border Olympia Municipal Airport Water Bodies (River - Small Scale) Water Bodies (Other) Parks Cities Capital Forest County Background Roads - Major <all other values> I 5 ACCESS; US 101 ACCESS; US 101 SB OFF RAMP I 5; US 101 Roads Railroads County Border Olympia Municipal Airport 2020© Thurston County The information included on this map has been compiled by Thurston County staff from a variety of sources and is subject to change without notice. Additional elements may be present in reality that are not represented on the map. Ortho-photos and other data may not align. The boundaries depicted by these datasets are approximate. This document is not intended for use as a survey product. ALL DATA IS EXPRESSLY PROVIDED ‘AS IS’ AND ‘WITH ALL FAULTS’. Thurston County makes no representations or warranties, express or implied, as to accuracy, completeness, timeliness, or rights to the use of such information. In no event shall Thurston County be liable for direct, indirect, incidental, consequential, special, or tort damages of any kind, including, but not limited to, lost revenues or lost profits, real or anticipated, resulting from the use, misuse or reliance of the information contained on this map. If any portion of this map or disclaimer is missing or altered, Thurston County removes itself from all responsibility from the map and the data contained within. The burden for determining fitness for use lies entirely with the user and the user is solely responsible for understanding the accuracy limitation of the information contained in this map. Authorized for 3rd Party reproduction for personal use only. FEMA FLOOD MAP 2,684Scale 1: 0 12/21/2020 Note: Legend 100 200 Feet Published: Map Created Using GeoData Public Website Flood Zones FEMA 100 Year (1%) 500 Year (0.2%) Parcel Boundaries Roads - Major (Large Scale) <all other values> I 5 ACCESS; US 101 ACCESS; US 101 SB OFF RAMP I 5; US 101 Roads (Large Scale) Railroads County Border Olympia Municipal Airport Water Bodies (River - Large Scale) Water Bodies (Other) Parks Cities Capital Forest County Background Roads - Major <all other values> I 5 ACCESS; US 101 ACCESS; US 101 SB OFF RAMP I 5; US 101 Roads Railroads County Border Olympia Municipal Airport 2020© Thurston County ATTACHMENT C Existing Conditions Map 3 3 7 3383353363373323333343293313283283283333343353 3 6 32933133232 8 328329327328337338338335336337331332333334329328330330330TSTSTSTSTSTSTSTSTSTSTSTSTSTSTSTSTBTBTBTBTBTBTBTBTBTBTBTBTBTBTBTBX X X X X X X AS BUILT CENTERLINEGRAVEL DRIVEWAY DIST U R B E D D R I V E W A Y 40" FIR 27" FIR40" FIR 18" FIR 46" FIR 28" FIR 30" FIR 11" FIR 21" FIR 28" FIR 24" FIR 26" FIR 30" FIR 32" FIR 22" FIR 48" FIR 28" FIR 24" FIR 28" FIR 20" FIR 26" FIR 19" FIR 28" FIR 16" FIR 16" FIR22" FIR 22" FIR 24" FIR 32" FIR 15" FIR 15" FIR RHOTON ROADS 89°28'57" W 2653.34' S 89°53'29" W 418.30'258.35 ' 2294.54'240.00'N 00°06'31" W2644.20'17 2019 18 TR 17N 02 19 ETHURSTON COUNTYPARCEL NO.64300800301.1102 RHOTON RD SE LOT 1SS-00-8255-YL FOUND 5/8" REBAR W/ CAP LS 24227 FOUND 1/2" REBAR W/ PUSHED OVER CAP FOUND 1/2" REBAR W/ PUSHED OVER CAP PP FOUND 5/8" REBAR W/ CAP LS 24227 30' NE CORNER OF SECTION 19CALCULATED PER SURVEYREFERENCE 1 CENTER 1/4 CORNER OF SECTION 19 FOUND CASED MONUMENT W/ 2" BRASS DISC W/ PUNCH LS 22346 N 1/4 CORNER OF SECTION 19 FOUND 1/2" IRON PIPE W/MPK BENCH MARK = 328.82'S 20 °22 '43 " E UAIL MEADOWS CT SE 946 QUAIL MEADOW CT SE 104 RHOTON CT NW 945 QUAIL MEADOW CT SE 22718430300 9246 RHOTON RD 64300800302 1002 RHOTON RD SE RHOTON ROADCULLENSROADKILLIONROADIIIIIIIIIIIIIIIIC A N A L R O A D C A N A L R O A D PROJECT SITE YELM CENT R A L I A CANA L YEL M C R E E K NISQUALLY RIVER YELM WA 1102 & 1002 RHOTON ROAD SE YELM, WA 98597 EXISTING CONDITIONS TPN 64300800301 & 64300800302 5016 Lacey Boulevard SE, Lacey, Washington 98503(360) 491-3399 Fax (360) 491-3857 MODERN RESOURCES LLC SITE DEVELOPMENT VERTICAL DATUMNAVD 88 ATTACHMENT D Proposed Conditions Map 5016 Lacey Boulevard SE, Lacey, Washington 98503(360) 491-3399 Fax (360) 491-3857 YELM WA PROPOSED CONDITIONS MODERN RESOURCES LLC COMMERCIAL SITE DEVELOPMENT ATTACHMENT E Construction Stormwater Pollution Prevention Plan (CSWPPP) i Construction Stormwater Pollution Prevention Plan (CSWPPP) Modern Resources LLC Site Development SC Project #20136 December 2020 Applicant / Owner: Modern Resources LLC 4810 Raccoon Valley Road Olympia, WA 98513 Contractor: _____________________________________ _____________________________________ _____________________________________ _________________________________________ Prepared By: Table of Contents Table of Contents ....................................................................................................................................... ii Project Description ..................................................................................................................................... 1 Construction Activities ............................................................................................................................... 1 TESC Element 1: Mark clearing limits. ................................................................................................ 2 TESC Element 2: Establish construction access. ................................................................................. 2 TESC Element 3: Control flow rates. ................................................................................................... 2 TESC Element 4: Install sediment controls. ........................................................................................ 2 TESC Element 5: Stabilize soils. .......................................................................................................... 3 TESC Element 6: Protect slopes. ......................................................................................................... 3 TESC Element 7: Protect Drain Inlets. ................................................................................................ 4 TESC Element 8: Stabilize channels and outlets. ................................................................................ 4 TESC Element 9: Control pollutants ................................................................................................... 4 TESC Element 10: Control Dewatering. .............................................................................................. 4 TESC Element 11: Maintain BMPs. ..................................................................................................... 5 TESC Element 12: Manage the project. .............................................................................................. 5 TESC Element 13: Protect Low Impact Development BMPs. ............................................................. 6 Appendix A – Vicinity Map Appendix B – Construction SWPPP TESC Drawings Appendix C – Best Management Practices (BMP’s) Project Description Modern Resources LLC is located at 1102 Rhoton Road SE, Yelm (TPN 64300800301 and 64300800302). The project consists of constructing a cabinet manufacturing facility, asphalt paved driveway and parking lot, gravel turnaround, retaining wall, water and sewer utility connections, stormwater drainage and infiltration, and landscaping areas driveway on existing undeveloped land. The work will be in conformance with the requirements of the 2019 SWMMWW adopted by the City of Yelm. Topography The site topography consists of mild slopes around the eastern portion of both parcels and flattens out around the western side. Vegetation Native Fir trees ranging between 11 and 48” in diameter populate along the northern boundary of parcel #64300800301, with the majority filling out the eastern-central portion of the parcel where the proposed development is to be located. Other native vegetation fills out the remainder of the site. Construction Activities The project involves the construction of a commercial cabinet manufacturing building with dimensions of 200’x100’. The construction activities are anticipated to include clearing and grubbing for the construction of a new building area, excavation and grading, the construction of the asphalt driveway, parking area, and offloading zone, gravel building perimeter, water and sewer utility connections, stormwater improvements, and landscaping. TESC Element 1: Preserving Natural Vegetation/Mark Clearing Limits. Prior to any site clearing or grading, all clearing limits, sensitive areas and their buffers, easements, setbacks, critical areas and their buffers, and trees that are to be preserved within the construction area will be clearly marked. All native vegetation, top soil, and duff layer shall be retained to maximum degree practicable. Refer to attached Site Plan. Applicable BMPs: C101: Preserving Natural Vegetation C102: Buffer Zones C103: High Visibility Fence C233: Silt Fence TESC Element 2: Establish construction access. Tracking of sediment onto paved roads will be minimized through constructing a construction access driveway approach off Alderwood Drive using crushed rock, CSBC, or gravel base. This entrance will be graded to a minimum of 6-inch depth and serve as the construction access. If sediment is transported onto a road surface, the road will be cleaned at the end of each work day or more often if necessary. Sediment will be removed from the roadway by sweeping or other comparable means. Washing of the sediment into the storm drainage system will not be allowed. Sweeping operations shall utilize moisture, as necessary, to limit the generation of dust. Applicable BMPs: C105: Stabilized Construction Access C106: Wheel Wash C107: Construction Road/Parking Area Stabilization TESC Element 3: Control flow rates. This project will consist of the construction of a new commercial development with a 20,000 square foot building, asphalt driveway and parking lot, utilities, stormwater treatment and detention, and retaining wall. Properties adjacent to the project site shall be protected from sediment deposition. During construction, these properties and downstream waterways shall be protected from erosion and the associated discharge of turbid waters due to increases in the velocity and peak volumetric flow rate of stormwater runoff from the project site. Install energy dissipation/filtration structures on sloped areas, steeper slopes will require closer placement of dissipation facilities. Install velocity dissipation structures to ensure reduction of flow velocity to a non-erosive level. Velocity of water leaving the site should not exceed 3 feet/second. Applicable BMPs: C235: Wattles TESC Element 4: Install sediment controls. Any necessary sediment control BMP’s shall be installed prior to any soil-disturbing activities. The intention of these controls is to retain sediment on the project site. Work activities will include excavation, material removal, and grading. Soil shall be prevented from leaving exposed and excavated areas. Wattles shall be installed on existing mild slopes for stabilization. Applicable BMPs: C233: Silt Fence C235: Wattles TESC Element 5: Stabilize soils. All exposed and unworked soils shall be stabilized by application of effective BMPs that protect the soil from the erosive forces of raindrop impact and flowing water, and wind erosion. Control stormwater volume and velocity within the site to minimize soil erosion. Control stormwater discharges, including peak flow and total volume, to minimize erosion at outlets and to minimize downstream channel and stream bank erosion. The number of days that soils can remain exposed and unworked is dependent on the time of year the construction is being done; from October 1 through April 30, no soils shall remain exposed and unworked for more than 2 days and from May 1 to September 30, no soils shall remain exposed and unworked for more than 7 days. Prior to leaving the site, stormwater runoff shall pass through a sediment pond or sediment trap, or other appropriate BMPs. This condition applies to all onsite soils, whether at final grade or not. Soils shall be stabilized at the end of the shift before a holiday or weekend if needed based on the weather forecast. Soil stockpiles shall be stabilized from erosion and protected with sediment trapping measures, and where possible, located away from storm drain inlets, waterways, and drainage channels. Minimize soil compaction and, unless infeasible, preserve topsoil. Applicable BMPs: C120: Temporary and Permanent Seeding C121: Mulching C124: Sodding C125: Topsoiling/Composting C130: Surface Roughening C140: Dust Control TESC Element 6: Protect slopes. The site consists of a flat terrain on the western portion, and moderate slopes on the eastern side. The following guidelines will also be observed throughout construction: • Consider soil type and its potential for erosion. • Off-site stormwater (run-on) shall be diverted away from slopes and disturbed areas with interceptor dikes and/or swales. Off-site stormwater should be managed separately from stormwater generated on the site. • Place excavated material on the uphill side of trenches, consistent with safety and space considerations. Applicable BMPs: BMP C120: Temporary and Permanent Seeding BMP C121: Mulching BMP C122: Nets and Blankets BMP C124: Sodding TESC Element 7: Protect Drain Inlets. It is anticipated that no protection of existing drain inlets will be needed for this project. Inlet drain protection will be used on all proposed stormwater inlets. Applicable BMPs: BMP C220: Inlet Protection TESC Element 8: Stabilize channels and outlets. It is anticipated that no temporary on-site conveyance channels will be needed for the project. Applicable BMPs: N/A TESC Element 9: Control pollutants Methods for controlling pollutants that can be considered hazardous materials, such as hydrocarbons and pH-modifying substances, must be described in the contractor’s SPCC plan. The plan must be prepared to meet Standard Specification 1-07.15(1) and the Washington State Department of Ecology’s (Ecology’s) standards as described in WSDOT SPCC Plan Preparation Instructions and Spill Plan Reviewers Protocols: “www.wsdot.wa.gov/Environment/HazMat/SpillPrevention.htm” Source pollutants and construction debris will be handled and disposed of in a manner that will not cause contamination of stormwater, surface waters, or ground water. Process water (for example, concrete washout, slurry water, and hydrodemolition) must be contained and cannot be discharged to waters of the state. Applicable BMPs: C151: Concrete Handling C152: Sawcutting and Surfacing Pollution Prevention C153: Material Delivery, Storage and Containment C154: Concrete Washout Area C250: Construction Stormwater Chemical Treatment C251: Construction Stormwater Filtration TESC Element 10: Control Dewatering. Ground water is not anticipated as part of this project. If groundwater is encountered in an excavation or other area, control, treat, and discharge it as described in WSDOT Standard Specification 8-01.3(1)C. Applicable BMPs: N/A TESC Element 11: Maintain BMPs. All temporary and permanent erosion and sediment control BMPs shall be maintained and repaired in order to assure continued performance of their intended function. All maintenance and repair shall be done in accordance with the BMP specifications or applicable standards. Sediment control BMPs shall be inspected weekly or after a runoff-producing event during the dry season and daily during the wet season. The inspection shall be performed by a Certified Erosion and Sediment Control Lead. Documentation of inspection and maintenance of BMPs should be kept in the Site Log Book. All temporary erosion and sediment control BMPs shall be removed with 30 days after final site stabilization is achieved or when the Engineer determines that the temporary BMP is no longer needed. Trapped sediment shall be removed from the site. Any soil areas disturbed when the BMPs are removed shall be permanently stabilized. Applicable BMPs: C150: Materials on Hand TESC Element 12: Manage the project. The following action shall apply to this project: Establish areas of clearing, grading, cutting, and filling in accordance with the site development plan. Minimize the removal of trees and disturbance of native soils and when establishing limits of disturbance. Phase development where feasible to prevent soil erosion and transport of sediment from the site during construction. Revegetate exposed areas and maintain vegetation as a part of the clearing activities for any phase. A CESCL must be identified in the SWPPP, and must be on site or on call at all times for this project. All BMPs are inspected, monitored, and maintained in accordance with TESC Element 11. The TESC and SPCC plans will be kept on-site or within reasonable access to the site. Due to the unpredictable nature of weather and construction conditions, the TESC plan is a flexible document that should be modified whenever field conditions change. Whenever inspections and/or monitoring reveal that the BMPs identified in the TESC plan are inadequate the plan must be modified. Most of these updates can be drawn onto the plan sheets. The plan must also be updated whenever there are changes in the project design or in construction methods that could affect the potential for erosion or spills. Maintaining an Updated Construction SWPPP - The Construction SWPPP shall be retained onsite or within reasonable access to the site. The SWPPP shall be modified whenever there is a significant change in the design, construction, operation, or maintenance at the construction site that has, or could have, a significant effect on the discharge of pollutants to waters of the state. The SWPPP shall be modified if during inspections or investigations conducted by the owner, the engineer or the City of Olympia, it is determined that the SWPPP is ineffective in eliminating or significantly minimizing pollutants in stormwater discharges from the site. The SWPPP shall be modified as necessary to include additional or modified BMPs designed to correct problems identified. Revisions to the SWPPP shall be completed within seven (7) calendar days following the inspection. If a Construction SWPPP is found to be inadequate (with respect to erosion and sediment control requirements), the City shall require that additional BMPs be implemented, as appropriate. Sequencing a construction project reduces the amount and duration of soil exposed to erosion by wind, rain, runoff, and vehicle tracking. The construction sequence schedule is an orderly listing of all major land-disturbing activities together with the necessary erosion and sedimentation control measures planned for the project. This type of schedule guides the contractor on work to be done before other work is started so that serious erosion and sedimentation problems can be avoided. Applicable BMPs: C160: Certified Erosion and Sediment Control Lead C162: Scheduling TESC Element 13: Protect Low Impact Development BMPs. Protect all LID BMPs from sedimentation through the installation and maintenance of erosion and sediment control BMPs on portions of the site that drain into the LID BMPs. Restoring BMPs must include removal of sediment and any sediment-laden Bioretention soils, and replacing the removed soils with soils meeting the design specification. Maintain the infiltration capabilities of LID BMPs by protecting against compaction by construction equipment and foot traffic. Protect completed lawn and landscaped areas from compaction due to construction equipment. Heavy equipment and foot traffic shall be kept off existing soils under LID BMPs that have been excavated to final grade to protect against compaction and preserve the infiltration rate of the soils. Applicable BMPs: C102: Buffer Zones C103: High-Visibility Fence C233: Silt Fence Appendix A Vicinity Map RHOTON ROADCULLENSROADKILLIONROADIIIIIIIIIIIIIIIIIIIIIIIC A N A L R O A D C A N A L R O A D PROJECT SITE YELM CENT R A L I A CAN A L YEL M C R E E K NISQUALLY RIVER Vicinity Map MODERN RESOURCES LLC SITE DEVELOPMENT 1102 RHOTON ROAD SE YELM, WA 98597 N.T.S. YELM, WA Appendix B Site Plan 3 3 7 3383353363373323333343293313283283283333343353 3 6 32933133232 8 328329327328337338338335336337331332333334329328330330330TSTSTSTSTSTSTSTSTSTSTSTSTSTSTSTSTBTBTBTBTBTBTBTBTBTBTBTBTBTBTBTBX X X X X X X AS BUILT CENTERLINEGRAVEL DRIVEWAY DIST U R B E D D R I V E W A Y 40" FIR 27" FIR40" FIR 18" FIR 46" FIR 28" FIR 30" FIR 11" FIR 21" FIR 28" FIR 24" FIR 26" FIR 30" FIR 32" FIR 22" FIR 48" FIR 28" FIR 24" FIR 28" FIR 20" FIR 26" FIR 19" FIR 28" FIR 16" FIR 16" FIR22" FIR 22" FIR 24" FIR 32" FIR 15" FIR 15" FIR RHOTON ROADS 89°28'57" W 2653.34' S 89°53'29" W 418.30'258.35 ' 2294.54'240.00'N 00°06'31" W2644.20'17 2019 18 TR 17N 02 19 ETHURSTON COUNTYPARCEL NO.64300800301.1102 RHOTON RD SE LOT 1SS-00-8255-YL FOUND 5/8" REBAR W/ CAP LS 24227 FOUND 1/2" REBAR W/ PUSHED OVER CAP FOUND 1/2" REBAR W/ PUSHED OVER CAP PP FOUND 5/8" REBAR W/ CAP LS 24227 30' NE CORNER OF SECTION 19CALCULATED PER SURVEYREFERENCE 1 CENTER 1/4 CORNER OF SECTION 19 FOUND CASED MONUMENT W/ 2" BRASS DISC W/ PUNCH LS 22346 N 1/4 CORNER OF SECTION 19 FOUND 1/2" IRON PIPE W/MPK BENCH MARK = 328.82'S 20 °22 '43 " E UAIL MEADOWS CT SE 946 QUAIL MEADOW CT SE 104 RHOTON CT NW 945 QUAIL MEADOW CT SE 22718430300 9246 RHOTON RD 64300800302 1002 RHOTON RD SE RHOTON ROADCULLENSROADKILLIONROADIIIIIIIIIIIIIIIIC A N A L R O A D C A N A L R O A D PROJECT SITE YELM CENT R A L I A CANA L YEL M C R E E K NISQUALLY RIVER YELM WA 1102 & 1002 RHOTON ROAD SE YELM, WA 98597 SITE PLAN, DRAINAGE, AND TESC TPN 64300800301 & 64300800302 5016 Lacey Boulevard SE, Lacey, Washington 98503(360) 491-3399 Fax (360) 491-3857 MODERN RESOURCES LLC SITE DEVELOPMENT VERTICAL DATUMNAVD 88 Appendix C Best Management Practices 12/21/2020 BMP C101: Preserving Natural Vegetation https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/3 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C101: Preserving Natural Vegetation BMP C101: Preserving Natural Vegetation Purpose The purpose of preserving natural vegetation is to reduce erosion wherever practicable. Limiting site disturbance is the single most effective method for reducing erosion. For example, conifers can hold up to about 50 percent of all rain that falls during a storm. Up to 20-30 percent of this rain may never reach the ground but is taken up by the tree or evaporates. Another benefit is that the rain held in the tree can be released slowly to the ground after the storm. Conditions of Use Natural vegetation should be preserved on steep slopes, near perennial and intermittent watercourses or swales, and on building sites in wooded areas. As required by local governments. Phase construction to preserve natural vegetation on the project site for as long as possible during the construction period. Design and Installation Specifications Natural vegetation can be preserved in natural clumps or as individual trees, shrubs and vines. The preservation of individual plants is more difficult because heavy equipment is generally used to remove unwanted vegetation. The points to remember when attempting to save individual plants are: Is the plant worth saving? Consider the location, species, size, age, vigor, and the work involved. Local governments may also have ordinances to save natural vegetation and trees. Fence or clearly mark areas around trees that are to be saved. It is preferable to keep ground disturbance away from the trees at least as far out as the dripline. Plants need protection from three kinds of injuries: Construction Equipment - This injury can be above or below the ground level. Damage results from scarring, cutting of roots, and compaction of the soil. Placing a fenced buffer zone around plants to be saved prior to construction can prevent construction equipment injuries. Grade Changes - Changing the natural ground level will alter grades, which affects the plant's ability to obtain the necessary air, water, and minerals. Minor fills usually do not cause problems although sensitivity 12/21/2020 BMP C101: Preserving Natural Vegetation https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/3 between species does vary and should be checked. Trees can typically tolerate fill of 6 inches or less. For shrubs and other plants, the fill should be less. When there are major changes in grade, it may become necessary to supply air to the roots of plants. This can be done by placing a layer of gravel and a tile system over the roots before the fill is made. The tile system should be laid out on the original grade leading from a dry well around the tree trunk. The system should then be covered with small stones to allow air to circulate over the root area. Lowering the natural ground level can seriously damage trees and shrubs. The highest percentage of the plant roots are in the upper 12 inches of the soil and cuts of only 2-3 inches can cause serious injury. To protect the roots it may be necessary to terrace the immediate area around the plants to be saved. If roots are exposed, construction of retaining walls may be needed to keep the soil in place. Plants can also be preserved by leaving them on an undisturbed, gently sloping mound. To increase the chances for survival, it is best to limit grade changes and other soil disturbances to areas outside the dripline of the plant. Excavations - Protect trees and other plants when excavating for drainfields, power, water, and sewer lines. Where possible, the trenches should be routed around trees and large shrubs. When this is not possible, it is best to tunnel under them. This can be done with hand tools or with power augers. If it is not possible to route the trench around plants to be saved, then the following should be observed: Cut as few roots as possible. When you have to cut, cut clean. Paint cut root ends with a wood dressing like asphalt base paint if roots will be exposed for more than 24-hours. Backfill the trench as soon as possible. Tunnel beneath root systems as close to the center of the main trunk to preserve most of the important feeder roots. Some problems that can be encountered with a few specific trees are: Maple, Dogwood, Red alder, Western hemlock, Western red cedar, and Douglas fir do not readily adjust to changes in environment and special care should be taken to protect these trees. The windthrow hazard of Pacific silver fir and madrona is high, while that of Western hemlock is moderate. The danger of windthrow increases where dense stands have been thinned. Other species (unless they are on shallow, wet soils less than 20 inches deep) have a low windthrow hazard. Cottonwoods, maples, and willows have water-seeking roots. These can cause trouble in sewer lines and infiltration fields. On the other hand, they thrive in high moisture conditions that other trees would not. Thinning operations in pure or mixed stands of Grand fir, Pacific silver fir, Noble fir, Sitka spruce, Western red cedar, Western hemlock, Pacific dogwood, and Red alder can cause serious disease problems. Disease can become established through damaged limbs, trunks, roots, and freshly cut stumps. Diseased and weakened trees are also susceptible to insect attack. Maintenance Standards 12/21/2020 BMP C101: Preserving Natural Vegetation https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…3/3 Inspect flagged and/or fenced areas regularly to make sure flagging or fencing has not been removed or damaged. If the flagging or fencing has been damaged or visibility reduced, it shall be repaired or replaced immediately and visibility restored. If tree roots have been exposed or injured, “prune” cleanly with an appropriate pruning saw or loppers directly above the damaged roots and recover with native soils. Treatment of sap flowing trees (fir, hemlock, pine, soft maples) is not advised as sap forms a natural healing barrier. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C102: Buffer Zones https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/2 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C102: Buffer Zones BMP C102: Buffer Zones Purpose Creation of an undisturbed area or strip of natural vegetation or an established suitable planting that will provide a living filter to reduce soil erosion and stormwater runoff velocities. Conditions of Use Buffer zones are used along streams, wetlands and other bodies of water that need protection from erosion and sedimentation. Contractors can use vegetative buffer zone BMPs to protect natural swales and they can incorporate them into the natural landscaping of an area. Do not use critical-areas buffer zones as sediment treatment areas. These areas shall remain completely undisturbed. The local permitting authority may expand the buffer widths temporarily to allow the use of the expanded area for removal of sediment. The types of buffer zones can change the level of protection required as shown below: Designated Critical Area Buffers - buffers that protect Critical Areas, as defined by the Washington State Growth Management Act, and are established and managed by the local permitting authority. These should not be disturbed and must protected with sediment control BMPs to prevent impacts. The local permitting authority may expand the buffer widths temporarily to allow the use of the expanded area for removal of sediment. Vegetative Buffer Zones - areas that may be identified in undisturbed vegetation areas or managed vegetation areas that are outside any Designated Critical Area Buffer. They may be utilized to provide an additional sediment control area and/or reduce runoff velocities. If being used for preservation of natural vegetation, they should be arranged in clumps or strips. They can be used to protect natural swales and incorporated into the natural landscaping area. Design and Installation Specifications Preserving natural vegetation or plantings in clumps, blocks, or strips is generally the easiest and most successful method. Leave all unstable steep slopes in natural vegetation. Mark clearing limits and keep all equipment and construction debris out of the natural areas and buffer zones. Steel construction fencing is the most effective method to protect sensitive areas and buffers. Alternatively, wire-backed silt fence on steel posts is marginally effective. Flagging alone is typically not effective. 12/21/2020 BMP C102: Buffer Zones https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/2 Keep all excavations outside the dripline of trees and shrubs. Do not push debris or extra soil into the buffer zone area because it will cause damage by burying and smothering vegetation. Vegetative buffer zones for streams, lakes or other waterways shall be established by the local permitting authority or other state or federal permits or approvals. Maintenance Standards Inspect the area frequently to make sure flagging remains in place and the area remains undisturbed. Replace all damaged flagging immediately. Remove all materials located in the buffer area that may impede the ability of the vegetation to act as a filter. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C103: High-Visibility Fence https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/2 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C103: High-Visibility Fence BMP C103: High-Visibility Fence Purpose High-visibility fencing is intended to: Restrict clearing to approved limits. Prevent disturbance of sensitive areas, their buffers, and other areas required to be left undisturbed. Limit construction traffic to designated construction entrances, exits, or internal roads. Protect areas where marking with survey tape may not provide adequate protection. Conditions of Use To establish clearing limits plastic, fabric, or metal fence may be used: At the boundary of sensitive areas, their buffers, and other areas required to be left uncleared. As necessary to control vehicle access to and on the site. Design and Installation Specifications High-visibility plastic fence shall be composed of a high-density polyethylene material and shall be at least four feet in height. Posts for the fencing shall be steel or wood and placed every 6 feet on center (maximum) or as needed to ensure rigidity. The fencing shall be fastened to the post every six inches with a polyethylene tie. On long continuous lengths of fencing, a tension wire or rope shall be used as a top stringer to prevent sagging between posts. The fence color shall be high-visibility orange. The fence tensile strength shall be 360 lbs/ft using the ASTM D4595 testing method. If appropriate install fabric silt fence in accordance with BMP C233: Silt Fence to act as high-visibility fence. Silt fence shall be at least 3 feet high and must be highly visible to meet the requirements of this BMP. Metal fences shall be designed and installed according to the manufacturer's specifications. Metal fences shall be at least 3 feet high and must be highly visible. Fences shall not be wired or stapled to trees. Maintenance Standards 12/21/2020 BMP C103: High-Visibility Fence https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/2 If the fence has been damaged or visibility reduced, it shall be repaired or replaced immediately and visibility restored. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C105: Stabilized Construction Access https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/4 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C105: Stabilized Construction Access BMP C105: Stabilized Construction Access Purpose Stabilized construction accesses are established to reduce the amount of sediment transported onto paved roads outside the project site by vehicles or equipment. This is done by constructing a stabilized pad of quarry spalls at entrances and exits for project sites. Conditions of Use Construction accesses shall be stabilized wherever traffic will be entering or leaving a construction site if paved roads or other paved areas are within 1,000 feet of the site. For residential subdivision construction sites, provide a stabilized construction access for each residence, rather than only at the main subdivision entrance. Stabilized surfaces shall be of sufficient length/width to provide vehicle access/parking, based on lot size and configuration. On large commercial, highway, and road projects, the designer should include enough extra materials in the contract to allow for additional stabilized accesses not shown in the initial Construction SWPPP. It is difficult to determine exactly where access to these projects will take place; additional materials will enable the contractor to install them where needed. Design and Installation Specifications See Figure II-3.1: Stabilized Construction Access for details. Note: the 100’ minimum length of the access shall be reduced to the maximum practicable size when the size or configuration of the site does not allow the full length (100’). Construct stabilized construction accesses with a 12-inch thick pad of 4-inch to 8-inch quarry spalls, a 4-inch course of asphalt treated base (ATB), or use existing pavement. Do not use crushed concrete, cement, or calcium chloride for construction access stabilization because these products raise pH levels in stormwater and concrete discharge to waters of the State is prohibited. A separation geotextile shall be placed under the spalls to prevent fine sediment from pumping up into the rock pad. The geotextile shall meet the standards listed in Table II-3.2: Stabilized Construction Access Geotextile Standards. Table II-3.2: Stabilized Construction Access Geotextile Standards Geotextile Property Required Value 12/21/2020 BMP C105: Stabilized Construction Access https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/4 Geotextile Property Required Value Grab Tensile Strength (ASTM D4751)200 psi min. Grab Tensile Elongation (ASTM D4632)30% max. Mullen Burst Strength (ASTM D3786-80a)400 psi min. AOS (ASTM D4751)20-45 (U.S. standard sieve size) Consider early installation of the first lift of asphalt in areas that will be paved; this can be used as a stabilized access. Also consider the installation of excess concrete as a stabilized access. During large concrete pours, excess concrete is often available for this purpose. Fencing (see BMP C103: High-Visibility Fence) shall be installed as necessary to restrict traffic to the construction access. Whenever possible, the access shall be constructed on a firm, compacted subgrade. This can substantially increase the effectiveness of the pad and reduce the need for maintenance. Construction accesses should avoid crossing existing sidewalks and back of walk drains if at all possible. If a construction access must cross a sidewalk or back of walk drain, the full length of the sidewalk and back of walk drain must be covered and protected from sediment leaving the site. Alternative Material Specification WSDOT has raised safety concerns about the Quarry Spall rock specified above. WSDOT observes that the 4- inch to 8-inch rock sizes can become trapped between Dually truck tires, and then released off-site at highway speeds. WSDOT has chosen to use a modified specification for the rock while continuously verifying that the Stabilized Construction Access remains effective. To remain effective, the BMP must prevent sediment from migrating off site. To date, there has been no performance testing to verify operation of this new specification. Jurisdictions may use the alternative specification, but must perform increased off-site inspection if they use, or allow others to use, it. Stabilized Construction Accesses may use material that meets the requirements of WSDOT's Standard Specifications for Road, Bridge, and Municipal Construction Section 9-03.9(1) (WSDOT, 2016) for ballast except for the following special requirements. The grading and quality requirements are listed in Table II-3.3: Stabilized Construction Access Alternative Material Requirements. Table II-3.3: Stabilized Construction Access Alternative Material Requirements Sieve Size Percent Passing 12/21/2020 BMP C105: Stabilized Construction Access https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…3/4 Sieve Size Percent Passing 2½″99-100 2″65-100 ¾″40-80 No. 4 5 max. No. 100 0-2 % Fracture 75 min. All percentages are by weight. The sand equivalent value and dust ratio requirements do not apply. The fracture requirement shall be at least one fractured face and will apply the combined aggregate retained on the No. 4 sieve in accordance with FOP for AASHTO T 335. Maintenance Standards Quarry spalls shall be added if the pad is no longer in accordance with the specifications. If the access is not preventing sediment from being tracked onto pavement, then alternative measures to keep the streets free of sediment shall be used. This may include replacement/cleaning of the existing quarry spalls, street sweeping, an increase in the dimensions of the access, or the installation of BMP C106: Wheel Wash. Any sediment that is tracked onto pavement shall be removed by shoveling or street sweeping. The sediment collected by sweeping shall be removed or stabilized on site. The pavement shall not be cleaned by washing down the street, except when high efficiency sweeping is ineffective and there is a threat to public safety. If it is necessary to wash the streets, the construction of a small sump to contain the wash water shall be considered. The sediment would then be washed into the sump where it can be controlled. Perform street sweeping by hand or with a high efficiency sweeper. Do not use a non-high efficiency mechanical sweeper because this creates dust and throws soils into storm systems or conveyance ditches. Any quarry spalls that are loosened from the pad, which end up on the roadway shall be removed immediately. If vehicles are entering or exiting the site at points other than the construction access(es), BMP C103: High- Visibility Fence shall be installed to control traffic. Upon project completion and site stabilization, all construction accesses intended as permanent access for maintenance shall be permanently stabilized. Figure II-3.1: Stabilized Construction Access 12/21/2020 BMP C105: Stabilized Construction Access https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…4/4 g pdf download Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did not pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions may choose not to accept these products, or may require additional testing prior to consideration for local use. Products that Ecology has approved as functionally equivalent are available for review on Ecology’s website at: https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-permittee-guidance- resources/Emerging-stormwater-treatment-technologies Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C106: Wheel Wash https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/2 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C106: Wheel Wash BMP C106: Wheel Wash Purpose Wheel washes reduce the amount of sediment transported onto paved roads by washing dirt from the wheels of motor vehicles prior to the motor vehicles leaving the construction site. Conditions of Use Use a wheel wash when BMP C105: Stabilized Construction Access is not preventing sediment from being tracked off site. Wheel washing is generally an effective BMP when installed with careful attention to topography. For example, a wheel wash can be detrimental if installed at the top of a slope abutting a right-of-way where the water from the dripping truck can run unimpeded into the street. Pressure washing combined with an adequately sized and surfaced pad with direct drainage to a large 10- foot x 10-foot sump can be very effective. Wheel wash wastewater is not stormwater. It is commonly called process water, and must be discharged to a separate on-site treatment system that prevents discharge to waters of the State, or to the sanitary sewer with local sewer district approval. Wheel washes may use closed-loop recirculation systems to conserve water use. Wheel wash wastewater shall not include wastewater from concrete washout areas. When practical, the wheel wash should be placed in sequence with BMP C105: Stabilized Construction Access. Locate the wheel wash such that vehicles exiting the wheel wash will enter directly onto BMP C105: Stabilized Construction Access. In order to achieve this, BMP C105: Stabilized Construction Access may need to be extended beyond the standard installation to meet the exit of the wheel wash. Design and Installation Specifications Suggested details are shown in Figure II-3.2: Wheel Wash. The Local Permitting Authority may allow other designs. A minimum of 6 inches of asphalt treated base (ATB) over crushed base material or 8 inches over a good subgrade is recommended to pave the wheel wash. Use a low clearance truck to test the wheel wash before paving. Either a belly dump or lowboy will work well to test clearance. 12/21/2020 BMP C106: Wheel Wash https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/2 Keep the water level from 12 to 14 inches deep to avoid damage to truck hubs and filling the truck tongues with water. Midpoint spray nozzles are only needed in extremely muddy conditions. Wheel wash systems should be designed with a small grade change, 6- to 12-inches for a 10-foot-wide pond, to allow sediment to flow to the low side of pond to help prevent re-suspension of sediment. A drainpipe with a 2- to 3-foot riser should be installed on the low side of the pond to allow for easy cleaning and refilling. Polymers may be used to promote coagulation and flocculation in a closed-loop system. Polyacrylamide (PAM) added to the wheel wash water at a rate of 0.25 - 0.5 pounds per 1,000 gallons of water increases effectiveness and reduces cleanup time. If PAM is already being used for dust or erosion control and is being applied by a water truck, the same truck can be used to change the wash water. Maintenance Standards The wheel wash should start out each day with fresh water. The wheel wash water should be changed a minimum of once per day. On large earthwork jobs where more than 10-20 trucks per hour are expected, the wheel wash water will need to be changed more often. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did not pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions may choose not to accept these products, or may require additional testing prior to consideration for local use. Products that Ecology has approved as functionally equivalent are available for review on Ecology’s website at: https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-permittee-guidance- resources/Emerging-stormwater-treatment-technologies Figure II-3.2: Wheel Wash pdf download Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C107: Construction Road / Parking Area Stabilization https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/2 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C107: Construction Road / Parking Area Stabilization BMP C107: Construction Road / Parking Area Stabilization Purpose Stabilizing roads, parking areas, and other on-site vehicle transportation routes immediately after grading reduces erosion caused by construction traffic or stormwater runoff. Conditions of Use Roads and parking areas shall be stabilized wherever they are constructed, whether permanent or temporary, for use by construction traffic. BMP C103: High-Visibility Fence shall be installed, if necessary, to limit the access of vehicles to only those roads and parking areas that are stabilized. Design and Installation Specifications On areas that will receive asphalt as part of the project, install the first lift as soon as possible. A 6-inch depth of 2- to 4-inch crushed rock, gravel base, or crushed surfacing base course shall be applied immediately after grading or utility installation. A 4-inch course of asphalt treated base (ATB) may also be used, or the road/parking area may be paved. It may also be possible to use cement or calcium chloride for soil stabilization. If cement or cement kiln dust is used for roadbase stabilization, pH monitoring and BMP C252: Treating and Disposing of High pH Water is necessary to evaluate and minimize the effects on stormwater. If the area will not be used for permanent roads, parking areas, or structures, a 6-inch depth of hog fuel may also be used, but this is likely to require more maintenance. Whenever possible, construction roads and parking areas shall be placed on a firm, compacted subgrade. Temporary road gradients shall not exceed 15 percent. Roadways shall be carefully graded to drain. Drainage ditches shall be provided on each side of the roadway in the case of a crowned section, or on one side in the case of a super-elevated section. Drainage ditches shall be directed to a sediment control BMP. Rather than relying on ditches, it may also be possible to grade the road so that runoff sheet-flows into a heavily vegetated area with a well-developed topsoil. Landscaped areas are not adequate. If this area has at least 50 feet of vegetation that water can flow through, then it is generally preferable to use the vegetation to treat runoff, rather than a sediment pond or trap. The 50 feet shall not include wetlands or their buffers. If runoff is allowed to sheetflow through adjacent vegetated areas, it is vital to design the roadways and parking areas so that no concentrated runoff is created. Storm drain inlets shall be protected to prevent sediment-laden water entering the drainage system (see BMP C220: Inlet Protection). 12/21/2020 BMP C107: Construction Road / Parking Area Stabilization https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/2 Maintenance Standards Inspect stabilized areas regularly, especially after large storm events. Crushed rock, gravel base, etc., shall be added as required to maintain a stable driving surface and to stabilize any areas that have eroded. Following construction, these areas shall be restored to pre-construction condition or better to prevent future erosion. Perform street cleaning at the end of each day or more often if necessary. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C120: Temporary and Permanent Seeding https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/6 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C120: Temporary and Permanent Seeding BMP C120: Temporary and Permanent Seeding Purpose Seeding reduces erosion by stabilizing exposed soils. A well-established vegetative cover is one of the most effective methods of reducing erosion. Conditions of Use Use seeding throughout the project on disturbed areas that have reached final grade or that will remain unworked for more than 30 days. The optimum seeding windows for western Washington are April 1 through June 30 and September 1 through October 1. Between July 1 and August 30 seeding requires irrigation until 75 percent grass cover is established. Between October 1 and March 30 seeding requires a cover of mulch or an erosion control blanket until 75 percent grass cover is established. Review all disturbed areas in late August to early September and complete all seeding by the end of September. Otherwise, vegetation will not establish itself enough to provide more than average protection. Mulch is required at all times for seeding because it protects seeds from heat, moisture loss, and transport due to runoff. Mulch can be applied on top of the seed or simultaneously by hydroseeding. See BMP C121: Mulching for specifications. Seed and mulch all disturbed areas not otherwise vegetated at final site stabilization. Final stabilization means the completion of all soil disturbing activities at the site and the establishment of a permanent vegetative cover, or equivalent permanent stabilization measures (such as pavement, riprap, gabions, or geotextiles) which will prevent erosion. See BMP T5.13: Post-Construction Soil Quality and Depth. Design and Installation Specifications General Install channels intended for vegetation before starting major earthwork and hydroseed with a Bonded Fiber Matrix. For vegetated channels that will have high flows, install erosion control blankets over the top of hydroseed. Before allowing water to flow in vegetated channels, establish 75 percent vegetation cover. If vegetated channels cannot be established by seed before water flow; install sod in the channel bottom — over top of hydromulch and erosion control blankets. 12/21/2020 BMP C120: Temporary and Permanent Seeding https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/6 Confirm the installation of all required surface water control measures to prevent seed from washing away. Hydroseed applications shall include a minimum of 1,500 pounds per acre of mulch with 3 percent tackifier. See BMP C121: Mulching for specifications. Areas that will have seeding only and not landscaping may need compost or meal-based mulch included in the hydroseed in order to establish vegetation. Re-install native topsoil on the disturbed soil surface before application. See BMP T5.13: Post-Construction Soil Quality and Depth. When installing seed via hydroseeding operations, only about 1/3 of the seed actually ends up in contact with the soil surface. This reduces the ability to establish a good stand of grass quickly. To overcome this, consider increasing seed quantities by up to 50 percent. Enhance vegetation establishment by dividing the hydromulch operation into two phases: Phase 1- Install all seed and fertilizer with 25-30 percent mulch and tackifier onto soil in the first lift. Phase 2- Install the rest of the mulch and tackifier over the first lift. Or, enhance vegetation by: Installing the mulch, seed, fertilizer, and tackifier in one lift. Spread or blow straw over the top of the hydromulch at a rate of 800-1000 pounds per acre. Hold straw in place with a standard tackifier. Both of these approaches will increase cost moderately but will greatly improve and enhance vegetative establishment. The increased cost may be offset by the reduced need for: Irrigation. Reapplication of mulch. Repair of failed slope surfaces. This technique works with standard hydromulch (1,500 pounds per acre minimum) and Bonded Fiber Matrix/ Mechanically Bonded Fiber Matrix (BFM/MBFMs) (3,000 pounds per acre minimum). Seed may be installed by hand if: Temporary and covered by straw, mulch, or topsoil. Permanent in small areas (usually less than 1 acre) and covered with mulch, topsoil, or erosion blankets. The seed mixes listed in Table II-3.4: Temporary and Permanent Seed Mixes include recommended mixes for both temporary and permanent seeding. Apply these mixes, with the exception of the wet area seed mix, at a rate of 120 pounds per acre. This rate can be reduced if soil amendments or slow-release fertilizers are used. Apply the wet area seed mix at a 12/21/2020 BMP C120: Temporary and Permanent Seeding https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…3/6 rate of 60 pounds per acre. Consult the local suppliers or the local conservation district for their recommendations. The appropriate mix depends on a variety of factors, including location, exposure, soil type, slope, and expected foot traffic. Alternative seed mixes approved by the local authority may be used, depending on the soil type and hydrology of the area. Table II-3.4: Temporary and Permanent Seed Mixes Common Name Latin Name % Weight % Purity % Germination Temporary Erosion Control Seed Mix A standard mix for areas requiring a temporary vegetative cover. Chewings or annual blue grass Festuca rubra var. commutata or Poa anna 40 98 90 Perennial rye Lolium perenne 50 98 90 Redtop or colonial bentgrass Agrostis alba or Agrostis tenuis 5 92 85 White dutch clover Trifolium repens 5 98 90 Landscaping Seed Mix A recommended mix for landscaping seed. Perennial rye blend Lolium perenne 70 98 90 Chewings and red fescue blend Festuca rubra var. commutata or Festuca rubra 30 98 90 Low-Growing Turf Seed Mix A turf seed mix for dry situations where there is no need for watering. This mix requires very little maintenance. Dwarf tall fescue (several varieties)Festuca arundinacea var.45 98 90 Dwarf perennial rye (Barclay)Lolium perenne var. barclay 30 98 90 Red fescue Festuca rubra 20 98 90 Colonial bentgrass Agrostis tenuis 5 98 90 Bioswale Seed Mix A seed mix for bioswales and other intermittently wet areas. Tall or meadow fescue Festuca arundinacea or Festuca elatior 75-80 98 90 Seaside/Creeping bentgrass Agrostis palustris 10-15 92 85 12/21/2020 BMP C120: Temporary and Permanent Seeding https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…4/6 Common Name Latin Name % Weight % Purity % Germination Redtop bentgrass Agrostis alba or Agrostis gigantea 5-10 90 80 Wet Area Seed Mix A low-growing, relatively non-invasive seed mix appropriate for very wet areas that are not regulated wetlands. Consult Hydraulic Permit Authority (HPA) for seed mixes if applicable. Tall or meadow fescue Festuca arundinacea or Festuca elatior 60-70 98 90 Seaside/Creeping bentgrass Agrostis palustris 10-15 98 85 Meadow foxtail Alepocurus pratensis 10-15 90 80 Alsike clover Trifolium hybridum 1-6 98 90 Redtop bentgrass Agrostis alba 1-6 92 85 Meadow Seed Mix A recommended meadow seed mix for infrequently maintained areas or non-maintained areas where colonization by native plants is desirable. Likely applications include rural road and utility right-of-way. Seeding should take place in September or very early October in order to obtain adequate establishment prior to the winter months. Consider the appropriateness of clover, a fairly invasive species, in the mix. Amending the soil can reduce the need for clover. Redtop or Oregon bentgrass Agrostis alba or Agrostis oregonensis 20 92 85 Red fescue Festuca rubra 70 98 90 White dutch clover Trifolium repens 10 98 90 Roughening and Rototilling The seedbed should be firm and rough. Roughen all soil no matter what the slope. Track walk slopes before seeding if engineering purposes require compaction. Backblading or smoothing of slopes greater than 4H:1V is not allowed if they are to be seeded. Restoration-based landscape practices require deeper incorporation than that provided by a simple single- pass rototilling treatment. Wherever practical, initially rip the subgrade to improve long-term permeability, infiltration, and water inflow qualities. At a minimum, permanent areas shall use soil amendments to achieve organic matter and permeability performance defined in engineered soil/landscape systems. For systems that are deeper than 8 inches complete the rototilling process in multiple lifts, or prepare the engineered soil system per specifications and place to achieve the specified depth. Fertilizers Conducting soil tests to determine the exact type and quantity of fertilizer is recommended. This will prevent the over-application of fertilizer. 12/21/2020 BMP C120: Temporary and Permanent Seeding https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…5/6 Organic matter is the most appropriate form of fertilizer because it provides nutrients (including nitrogen, phosphorus, and potassium) in the least water-soluble form. In general, use 10-4-6 N-P-K (nitrogen-phosphorus-potassium) fertilizer at a rate of 90 pounds per acre. Always use slow-release fertilizers because they are more efficient and have fewer environmental impacts. Do not add fertilizer to the hydromulch machine, or agitate, more than 20 minutes before use. Too much agitation destroys the slow-release coating. There are numerous products available that take the place of chemical fertilizers. These include several with seaweed extracts that are beneficial to soil microbes and organisms. If 100 percent cottonseed meal is used as the mulch in hydroseed, chemical fertilizer may not be necessary. Cottonseed meal provides a good source of long-term, slow-release, available nitrogen. Bonded Fiber Matrix and Mechanically Bonded Fiber Matrix On steep slopes use Bonded Fiber Matrix (BFM) or Mechanically Bonded Fiber Matrix (MBFM) products. Apply BFM/MBFM products at a minimum rate of 3,000 pounds per acre with approximately 10 percent tackifier. Achieve a minimum of 95 percent soil coverage during application. Numerous products are available commercially. Most products require 24-36 hours to cure before rainfall and cannot be installed on wet or saturated soils. Generally, products come in 40-50 pound bags and include all necessary ingredients except for seed and fertilizer. Install products per manufacturer's instructions. BFMs and MBFMs provide good alternatives to blankets in most areas requiring vegetation establishment. Advantages over blankets include: BFM and MBFMs do not require surface preparation. Helicopters can assist in installing BFM and MBFMs in remote areas. On slopes steeper than 2.5H:1V, blanket installers may require ropes and harnesses for safety. Installing BFM and MBFMs can save at least $1,000 per acre compared to blankets. Maintenance Standards Reseed any seeded areas that fail to establish at least 75 percent cover (100 percent cover for areas that receive sheet or concentrated flows). If reseeding is ineffective, use an alternate method such as sodding, mulching, nets, or blankets. Reseed and protect by mulch any areas that experience erosion after achieving adequate cover. Reseed and protect by mulch any eroded area. Supply seeded areas with adequate moisture, but do not water to the extent that it causes runoff. Approved as Functionally Equivalent 12/21/2020 BMP C120: Temporary and Permanent Seeding https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…6/6 Ecology has approved products as able to meet the requirements of this BMP. The products did not pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions may choose not to accept these products, or may require additional testing prior to consideration for local use. Products that Ecology has approved as functionally equivalent are available for review on Ecology’s website at: https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-permittee-guidance- resources/Emerging-stormwater-treatment-technologies Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C121: Mulching https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/4 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C121: Mulching BMP C121: Mulching Purpose Mulching soils provides immediate temporary protection from erosion. Mulch also enhances plant establishment by conserving moisture, holding fertilizer, seed, and topsoil in place, and moderating soil temperatures. There are a variety of mulches that can be used. This section discusses only the most common types of mulch. Conditions of Use As a temporary cover measure, mulch should be used: For less than 30 days on disturbed areas that require cover. At all times for seeded areas, especially during the wet season and during the hot summer months. During the wet season on slopes steeper than 3H:1V with more than 10 feet of vertical relief. Mulch may be applied at any time of the year and must be refreshed periodically. For seeded areas, mulch may be made up of 100 percent: cottonseed meal; fibers made of wood, recycled cellulose, hemp, or kenaf; compost; or blends of these. Tackifier shall be plant-based, such as guar or alpha plantago, or chemical-based such as polyacrylamide or polymers. Generally, mulches come in 40-50 pound bags. Seed and fertilizer are added at time of application. Recycled cellulose may contain polychlorinated biphenyl (PCBs). Ecology recommends that products should be evaluated for PCBs prior to use. Refer to BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection for conditions of use. PAM shall not be directly applied to water or allowed to enter a water body. Any mulch or tackifier product used shall be installed per the manufacturer’s instructions. Design and Installation Specifications 12/21/2020 BMP C121: Mulching https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/4 For mulch materials, application rates, and specifications, see Table II-3.6: Mulch Standards and Guidelines. Consult with the local supplier or the local conservation district for their recommendations. Increase the application rate until the ground is 95% covered (i.e. not visible under the mulch layer). Note: Thickness may be increased for disturbed areas in or near sensitive areas or other areas highly susceptible to erosion. Where the option of “Compost” is selected, it should be a coarse compost that meets the size gradations listed in Table II-3.5: Size Gradations of Compost as Mulch Material when tested in accordance with Test Method 02.02-B found in Test Methods for the Examination of Composting and Compost (Thompson, 2001). Table II-3.5: Size Gradations of Compost as Mulch Material Sieve Size Percent Passing 3"100% 1"90% - 100% 3/4"70% - 100% 1/4"40% - 100% Mulch used within the ordinary high-water mark of surface waters should be selected to minimize potential flotation of organic matter. Composted organic materials have higher specific gravities (densities) than straw, wood, or chipped material. Consult the Hydraulic Permit Authority (HPA) for mulch mixes if applicable. Maintenance Standards The thickness of the mulch cover must be maintained. Any areas that experience erosion shall be remulched and/or protected with a net or blanket. If the erosion problem is drainage related, then the problem shall be fixed and the eroded area remulched. Table II-3.6: Mulch Standards and Guidelines Mulch Material Guideline Description Straw Quality Standards Air-dried; free from undesirable seed and coarse material. Application Rates 2"-3" thick; 5 bales per 1,000 sf or 2-3 tons per acre 12/21/2020 BMP C121: Mulching https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…3/4 Mulch Material Guideline Description Remarks Cost-effective protection when applied with adequate thickness. Hand-application generally requires greater thickness than blown straw. The thickness of straw may be reduced by half when used in conjunction with seeding. In windy areas straw must be held in place by crimping, using a tackifier, or covering with netting. Blown straw always has to be held in place with a tackifier as even light winds will blow it away. Straw, however, has several deficiencies that should be considered when selecting mulch materials. It often introduces and/or encourages the propagation of weed species and it has no significant long-term benefits It should also not be used within the ordinary high-water elevation of surface waters (due to flotation). Hydromulch Quality Standards No growth inhibiting factors. Application Rates Approx. 35-45 lbs per 1,000 sf or 1,500 - 2,000 lbs per acre Remarks Shall be applied with hydromulcher. Shall not be used without seed and tackifier unless the application rate is at least doubled. Fibers longer than about 3/4 - 1 inch clog hydromulch equipment. Fibers should be kept to less than 3/4 inch. Compost Quality Standards No visible water or dust during handling. Must be produced per WAC 173-350, Solid Waste Handling Standards, but may have up to 35% biosolids. Application Rates 2" thick min.; approx. 100 tons per acre (approx. 750 lbs per cubic yard) Remarks More effective control can be obtained by increasing thickness to 3". Excellent mulch for protecting final grades until landscaping because it can be directly seeded or tilled into soil as an amendment. Compost used for mulch has a coarser size gradation than compost used for BMP C125: Topsoiling / Composting or BMP T5.13: Post-Construction Soil Quality and Depth. It is more stable and practical to use in wet areas and during rainy weather conditions. Do not use near wetlands or near phosphorous impaired water bodies. Chipped Site Vegetation Quality Standards Gradations from fines to 6 inches in length for texture, variation, and interlocking properties. Include a mix of various sizes so that the average size is between 2- and 4- inches. Application Rates 2" thick min.; Remarks This is a cost-effective way to dispose of debris from clearing and grubbing, and it eliminates the problems associated with burning. Generally, it should not be used on slopes above approx. 10% because of its tendency to be transported by runoff. It is not recommended within 200 feet of surface waters. If permanent seeding or planting is expected shortly after mulch, the decomposition of the chipped vegetation may tie up nutrients important to grass establishment. Note: thick application of this material over existing grass, herbaceous species, and some groundcovers could smother and kill vegetation. Wood- Based Mulch Quality Standards No visible water or dust during handling. Must be purchased from a supplier with a Solid Waste Handling Permit or one exempt from solid waste regulations. 12/21/2020 BMP C121: Mulching https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…4/4 Mulch Material Guideline Description Application Rates 2" thick min.; approx. 100 tons per acre (approx. 750 lbs. per cubic yard) Remarks This material is often called "wood straw" or "hog fuel". The use of mulch ultimately improves the organic matter in the soil. Special caution is advised regarding the source and composition of wood-based mulches. Its preparation typically does not provide any weed seed control, so evidence of residual vegetation in its composition or known inclusion of weed plants or seeds should be monitored and prevented (or minimized). Wood Strand Mulch Quality Standards A blend of loose, long, thin wood pieces derived from native conifer or deciduous trees with high length-to-width ratio. Application Rates 2" thick min. Remarks Cost-effective protection when applied with adequate thickness. A minimum of 95-percent of the wood strand shall have lengths between 2 and 10-inches, with a width and thickness between 1/16 and 1/2-inches. The mulch shall not contain resin, tannin, or other compounds in quantities that would be detrimental to plant life. Sawdust or wood shavings shall not be used as mulch. [Specification 9-14.4(4) from the Standard Specifications for Road, Bridge, and Municipal Construction (WSDOT, 2016) Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C122: Nets and Blankets https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/4 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C122: Nets and Blankets BMP C122: Nets and Blankets Purpose Erosion control nets and blankets are intended to prevent erosion and hold seed and mulch in place on steep slopes and in channels so that vegetation can become well established. In addition, some nets and blankets can be used to permanently reinforce turf to protect drainage ways during high flows. Nets (commonly called matting) are strands of material woven into an open, but high-tensile strength net (for example, coconut fiber matting). Blankets are strands of material that are not tightly woven, but instead form a layer of interlocking fibers, typically held together by a biodegradable or photodegradable netting (for example, excelsior or straw blankets). They generally have lower tensile strength than nets, but cover the ground more completely. Coir (coconut fiber) fabric comes as both nets and blankets. Conditions of Use Erosion control netting and blankets shall be made of natural plant fibers unaltered by synthetic materials. Erosion control nets and blankets should be used: To aid permanent vegetated stabilization of slopes 2H:1V or greater and with more than 10 feet of vertical relief. For drainage ditches and swales (highly recommended). The application of appropriate netting or blanket to drainage ditches and swales can protect bare soil from channelized runoff while vegetation is established. Nets and blankets also can capture a great deal of sediment due to their open, porous structure. Nets and blankets can be used to permanently stabilize channels and may provide a cost-effective, environmentally preferable alternative to riprap. Disadvantages of nets and blankets include: Surface preparation is required. On slopes steeper than 2.5H:1V, net and blanket installers may need to be roped and harnessed for safety. They cost at least $4,000-6,000 per acre installed. Advantages of nets and blankets include: Installation without mobilizing special equipment. Installation by anyone with minimal training Installation in stages or phases as the project progresses. 12/21/2020 BMP C122: Nets and Blankets https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/4 Installers can hand place seed and fertilizer as they progress down the slope. Installation in any weather. There are numerous types of nets and blankets that can be designed with various parameters in mind. Those parameters include: fiber blend, mesh strength, longevity, biodegradability, cost, and availability. An alternative to nets and blankets in some limited conditions is BMP C202: Riprap Channel Lining. Ensure that BMP C202: Riprap Channel Lining is appropriate before using it as a substitute for nets and blankets. Design and Installation Specifications See Figure II-3.3: Channel Installation (Clackamas County et al., 2008) and Figure II-3.4: Slope Installation for typical orientation and installation of nets and blankets used in channels and as slope protection. Note: these are typical only; all nets and blankets must be installed per manufacturer’s installation instructions. Installation is critical to the effectiveness of these products. If good ground contact is not achieved, runoff can concentrate under the product, resulting in significant erosion. Installation of nets and blankets on slopes: 1. Complete final grade and track walk up and down the slope. 2. Install hydromulch with seed and fertilizer. 3. Dig a small trench, approximately 12 inches wide by 6 inches deep along the top of the slope. 4. Install the leading edge of the net/blanket into the small trench and staple approximately every 18 inches. NOTE: Staples are metal, “U”-shaped, and a minimum of 6 inches long. Longer staples are used in sandy soils. Biodegradable stakes are also available. 5. Roll the net/blanket slowly down the slope as the installer walks backward. NOTE: The net/blanket rests against the installer’s legs. Staples are installed as the net/blanket is unrolled. It is critical that the proper staple pattern is used for the net/blanket being installed. The net/blanket is not to be allowed to roll down the slope on its own as this stretches the net/blanket, making it impossible to maintain soil contact. In addition, no one is allowed to walk on the net/blanket after it is in place. 6. If the net/blanket is not long enough to cover the entire slope length, the trailing edge of the upper net/blanket should overlap the leading edge of the lower net/blanket and be stapled. On steeper slopes, this overlap should be installed in a small trench, stapled, and covered with soil. With the variety of products available, it is impossible to cover all the details of appropriate use and installation. Therefore, it is critical that the designer consult the manufacturer's information and that a site visit takes place in order to ensure that the product specified is appropriate. Information is also available in WSDOT's Standard Specifications for Road, Bridge, and Municipal Construction Division 8-01 and Division 9-14 (WSDOT, 2016). 12/21/2020 BMP C122: Nets and Blankets https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…3/4 Use jute matting in conjunction with mulch (BMP C121: Mulching). Excelsior, woven straw blankets and coir (coconut fiber) blankets may be installed without mulch. There are many other types of erosion control nets and blankets on the market that may be appropriate in certain circumstances. In general, most nets (e.g., jute matting) require mulch in order to prevent erosion because they have a fairly open structure. Blankets typically do not require mulch because they usually provide complete protection of the surface. Extremely steep, unstable, wet, or rocky slopes are often appropriate candidates for use of synthetic blankets, as are riverbanks, beaches and other high-energy environments. If synthetic blankets are used, the soil should be hydromulched first. 100-percent biodegradable blankets are available for use in sensitive areas. These organic blankets are usually held together with a paper or fiber mesh and stitching which may last up to a year. Most netting used with blankets is photodegradable, meaning it breaks down under sunlight (not UV stabilized). However, this process can take months or years even under bright sun. Once vegetation is established, sunlight does not reach the mesh. It is not uncommon to find non-degraded netting still in place several years after installation. This can be a problem if maintenance requires the use of mowers or ditch cleaning equipment. In addition, birds and small animals can become trapped in the netting. Maintenance Standards Maintain good contact with the ground. Erosion must not occur beneath the net or blanket. Repair and staple any areas of the net or blanket that are damaged or not in close contact with the ground. Fix and protect eroded areas if erosion occurs due to poorly controlled drainage. Figure II-3.3: Channel Installation pdf download Figure II-3.4: Slope Installation pdf download Washington State Department of Ecology 12/21/2020 BMP C122: Nets and Blankets https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…4/4 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C124: Sodding https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/2 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C124: Sodding BMP C124: Sodding Purpose The purpose of sodding is to establish turf for immediate erosion protection and to stabilize drainage paths where concentrated overland flow will occur. Conditions of Use Sodding may be used in the following areas: Disturbed areas that require short-term or long-term cover. Disturbed areas that require immediate vegetative cover. All waterways that require vegetative lining. Waterways may also be seeded rather than sodded, and protected with a net or blanket. Design and Installation Specifications Sod shall be free of weeds, of uniform thickness (approximately 1-inch thick), and shall have a dense root mat for mechanical strength. The following steps are recommended for sod installation: 1. Shape and smooth the surface to final grade in accordance with the approved grading plan. Consider any areas (such as swales) that need to be overexcavated below design elevation to allow room for placing soil amendment and sod. 2. Amend 4 inches (minimum) of compost into the top 8 inches of the soil if the organic content of the soil is less than ten percent or the permeability is less than 0.6 inches per hour. See https://ecology.wa.gov/Waste-Toxics/Reducing-recycling-waste/Organic-materials/Managing-organics- compost for further information. 3. Fertilize according to the sod supplier's recommendations. 4. Work lime and fertilizer 1 to 2 inches into the soil, and smooth the surface. 5. Lay strips of sod beginning at the lowest area to be sodded and perpendicular to the direction of water flow. Wedge strips securely into place. Square the ends of each strip to provide for a close, tight fit. Stagger joints at least 12 inches. Staple on slopes steeper than 3H:1V. Staple the upstream edge of each sod strip. 12/21/2020 BMP C124: Sodding https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/2 6. Roll the sodded area and irrigate. 7. When sodding is carried out in alternating strips or other patterns, seed the areas between the sod immediately after sodding. Maintenance Standards If the grass is unhealthy, the cause shall be determined and appropriate action taken to reestablish a healthy groundcover. If it is impossible to establish a healthy groundcover due to frequent saturation, instability, or some other cause, the sod shall be removed, the area seeded with an appropriate mix, and protected with a net or blanket. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C125: Topsoiling / Composting https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/4 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C125: Topsoiling / Composting BMP C125: Topsoiling / Composting Purpose Topsoiling and composting provide a suitable growth medium for final site stabilization with vegetation. While not a permanent cover practice in itself, topsoiling and composting are an integral component of providing permanent cover in those areas where there is an unsuitable soil surface for plant growth. Use this BMP in conjunction with other BMPs such as BMP C120: Temporary and Permanent Seeding, BMP C121: Mulching, or BMP C124: Sodding. Implementation of this BMP may meet the post-construction requirements of BMP T5.13: Post- Construction Soil Quality and Depth. Native soils and disturbed soils that have been organically amended not only retain much more stormwater, but also serve as effective biofilters for urban pollutants and, by supporting more vigorous plant growth, reduce the water, fertilizer and pesticides needed to support installed landscapes. Topsoil does not include any subsoils but only the material from the top several inches including organic debris. Conditions of Use Permanent landscaped areas shall contain healthy topsoil that reduces the need for fertilizers, improves overall topsoil quality, provides for better vegetative health and vitality, improves hydrologic characteristics, and reduces the need for irrigation. Leave native soils and the duff layer undisturbed to the maximum extent practicable. Stripping of existing, properly functioning soil system and vegetation for the purpose of topsoiling during construction is not acceptable. Preserve existing soil systems in undisturbed and uncompacted conditions if functioning properly. Areas that already have good topsoil, such as undisturbed areas, do not require soil amendments. Restore, to the maximum extent practical, native soils disturbed during clearing and grading to a condition equal to or better than the original site condition’s moisture-holding capacity. Use on-site native topsoil, incorporate amendments into on-site soil, or import blended topsoil to meet this requirement. Topsoiling is a required procedure when establishing vegetation on shallow soils, and soils of critically low pH (high acid) levels. Beware of where the topsoil comes from, and what vegetation was on site before disturbance. Invasive plant seeds may be included and could cause problems for establishing native plants, landscaped areas, or grasses. Topsoil from the site will contain mycorrhizal bacteria that are necessary for healthy root growth and nutrient transfer. These native mycorrhiza are acclimated to the site and will provide optimum conditions for 12/21/2020 BMP C125: Topsoiling / Composting https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/4 establishing grasses. Use commercially available mycorrhiza products when using off-site topsoil. Design and Installation Specifications Meet the following requirements for disturbed areas that will be developed as lawn or landscaped areas at the completed project site: Maximize the depth of the topsoil wherever possible to provide the maximum possible infiltration capacity and beneficial growth medium. Topsoil shall have: A minimum depth of 8-inches. Scarify subsoils below the topsoil layer at least 4-inches with some incorporation of the upper material to avoid stratified layers, where feasible. Ripping or re-structuring the subgrade may also provide additional benefits regarding the overall infiltration and interflow dynamics of the soil system. A minimum organic content of 10% dry weight in planting beds, and 5% organic matter content in turf areas. Incorporate organic amendments to a minimum 8-inch depth except where tree roots or other natural features limit the depth of incorporation. A pH between 6.0 and 8.0 or matching the pH of the undisturbed soil. If blended topsoil is imported, then fines should be limited to 25 percent passing through a 200 sieve. Mulch planting beds with 2 inches of organic material Accomplish the required organic content, depth, and pH by returning native topsoil to the site, importing topsoil of sufficient organic content, and/or incorporating organic amendments. When using the option of incorporating amendments to meet the organic content requirement, use compost that meets the compost specification for Bioretention (See BMP T7.30: Bioretention), with the exception that the compost may have up to 35% biosolids or manure. Sections 3 through 7 of Building Soil: Guidelines and Resources for Implementing Soil Quality and Depth BMP T5.13 in WDOE Stormwater Management Manual for Western Washington (Stenn et al., 2016), provides useful guidance for implementing whichever option is chosen. It includes guidance for pre- approved default strategies and guidance for custom strategies. Check with your local jurisdiction concerning its acceptance of this guidance. The final composition and construction of the soil system will result in a natural selection or favoring of certain plant species over time. For example, incorporation of topsoil may favor grasses, while layering with mildly acidic, high-carbon amendments may favor more woody vegetation. Allow sufficient time in scheduling for topsoil spreading prior to seeding, sodding, or planting. Take care when applying top soil to subsoils with contrasting textures. Sandy topsoil over clayey subsoil is a particularly poor combination, as water creeps along the junction between the soil layers and causes the topsoil to slough. If topsoil and subsoil are not properly bonded, water will not infiltrate the soil profile evenly and it will be difficult to establish vegetation. The best method to promote bonding is to actually work the topsoil into the layer below for a depth of at least 6 inches. 12/21/2020 BMP C125: Topsoiling / Composting https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…3/4 Field exploration of the site shall be made to determine if there is surface soil of sufficient quantity and quality to justify stripping. Topsoil shall be friable and loamy (loam, sandy loam, silt loam, sandy clay loam, and clay loam). Avoid areas of natural ground water recharge. Stripping shall be confined to the immediate construction area. A 4-inch to 6-inch stripping depth is common, but depth may vary depending on the particular soil. All surface runoff control structures shall be in place prior to stripping. Do not place topsoil while in a frozen or muddy condition, when the subgrade is excessively wet, or when conditions exist that may otherwise be detrimental to proper grading or proposed sodding or seeding. In any areas requiring grading, remove and stockpile the duff layer and topsoil on site in a designated, controlled area, not adjacent to public resources and critical areas. Reapply stockpiled topsoil to other portions of the site where feasible. Locate the topsoil stockpile so that it meets specifications and does not interfere with work on the site. It may be possible to locate more than one pile in proximity to areas where topsoil will be used. Stockpiling of topsoil shall occur in the following manner: Side slopes of the stockpile shall not exceed 2H:1V. Between October 1 and April 30: An interceptor dike with gravel outlet and silt fence shall surround all topsoil. Within 2 days complete erosion control seeding, or covering stockpiles with clear plastic, or other mulching materials. Between May 1 and September 30: An interceptor dike with gravel outlet and silt fence shall surround all topsoil if the stockpile will remain in place for a longer period of time than active construction grading. Within 7 days complete erosion control seeding, or covering stockpiles with clear plastic, or other mulching materials. When native topsoil is to be stockpiled and reused the following should apply to ensure that the mycorrhizal bacterial, earthworms, and other beneficial organisms will not be destroyed: Re-install topsoil within 4 to 6 weeks. Do not allow the saturation of topsoil with water. Do not use plastic covering. Maintenance Standards Inspect stockpiles regularly, especially after large storm events. Stabilize any areas that have eroded. 12/21/2020 BMP C125: Topsoiling / Composting https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…4/4 Establish soil quality and depth toward the end of construction and once established, protect from compaction, such as from large machinery use, and from erosion. Plant and mulch soil after installation. Leave plant debris or its equivalent on the soil surface to replenish organic matter. Reduce and adjust, where possible, the use of irrigation, fertilizers, herbicides and pesticides, rather than continuing to implement formerly established practices. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C130: Surface Roughening https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/2 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C130: Surface Roughening BMP C130: Surface Roughening Purpose Surface roughening aids in the establishment of vegetative cover, reduces runoff velocity, increases infiltration, and provides for sediment trapping through the provision of a rough soil surface. Horizontal depressions are created by operating a tiller or other suitable equipment on the contour or by leaving slopes in a roughened condition by not fine grading them. Use this BMP in conjunction with other BMPs such as BMP C120: Temporary and Permanent Seeding, BMP C121: Mulching, or BMP C124: Sodding. Conditions for Use All slopes steeper than 3H:1V and greater than 5 vertical feet require surface roughening to a depth of 2 to 4 inches prior to seeding. Areas that will not be stabilized immediately may be roughened to reduce runoff velocity until seeding takes place. Slopes with a stable rock face do not require roughening. Slopes where mowing is planned should not be excessively roughened. Design and Installation Specifications There are different methods for achieving a roughened soil surface on a slope, and the selection of an appropriate method depends upon the type of slope. Roughening methods include stair-step grading, grooving, contour furrows, and tracking. See Figure II-3.5: Surface Roughening by Tracking and Contour Furrows. Factors to be considered in choosing a roughening method are slope steepness, mowing requirements, and whether the slope is formed by cutting or filling. Disturbed areas that will not require mowing may be stair-step graded, grooved, or left rough after filling. Stair-step grading is particularly appropriate in soils containing large amounts of soft rock. Each "step" catches material that sloughs from above, and provides a level site where vegetation can become established. Stairs should be wide enough to work with standard earth moving equipment. Stair steps must be on contour or gullies will form on the slope. Areas that will be mowed (these areas should have slopes less steep than 3H:1V) may have small furrows left by disking, harrowing, raking, or seed-planting machinery operated on the contour. 12/21/2020 BMP C130: Surface Roughening https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/2 Graded areas with slopes steeper than 3H:1V but less than 2H:1V should be roughened before seeding. This can be accomplished in a variety of ways, including "track walking," or driving a crawler tractor up and down the slope, leaving a pattern of cleat imprints parallel to slope contours. Tracking is done by operating equipment up and down the slope to leave horizontal depressions in the soil. Maintenance Standards Areas that are surface roughened should be seeded as quickly as possible. Regular inspections should be made of the area. If rills appear, they should be re-roughened and re-seeded immediately. Figure II-3.5: Surface Roughening by Tracking and Contour Furrows pdf download Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C140: Dust Control https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/2 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C140: Dust Control BMP C140: Dust Control Purpose Dust control prevents wind transport of dust from disturbed soil surfaces onto roadways, drainage ways, and surface waters. Conditions of Use Use dust control in areas (including roadways) subject to surface and air movement of dust where on-site or off- site impacts to roadways, drainage ways, or surface waters are likely. Design and Installation Specifications Vegetate or mulch areas that will not receive vehicle traffic. In areas where planting, mulching, or paving is impractical, apply gravel or landscaping rock. Limit dust generation by clearing only those areas where immediate activity will take place, leaving the remaining area(s) in the original condition. Maintain the original ground cover as long as practical. Construct natural or artificial windbreaks or windscreens. These may be designed as enclosures for small dust sources. Sprinkle the site with water until the surface is wet. Repeat as needed. To prevent carryout of mud onto the street, refer to BMP C105: Stabilized Construction Access and BMP C106: Wheel Wash. Irrigation water can be used for dust control. Irrigation systems should be installed as a first step on sites where dust control is a concern. Spray exposed soil areas with a dust palliative, following the manufacturer’s instructions and cautions regarding handling and application. Used oil is prohibited from use as a dust suppressant. Local governments may approve other dust palliatives such as calcium chloride or PAM. PAM (BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection) added to water at a rate of 0.5 pounds per 1,000 gallons of water per acre and applied from a water truck is more effective than water alone. This is due to increased infiltration of water into the soil and reduced evaporation. In addition, small soil particles are bonded together and are not as easily transported by wind. Adding PAM may reduce the quantity of water needed for dust control. Note that the application rate specified here applies to this BMP, and is not the same application rate that is specified in BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection, but the downstream protections still apply. 12/21/2020 BMP C140: Dust Control https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/2 Refer to BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection for conditions of use. PAM shall not be directly applied to water or allowed to enter a water body. Contact your local Air Pollution Control Authority for guidance and training on other dust control measures. Compliance with the local Air Pollution Control Authority constitutes compliance with this BMP. Use vacuum street sweepers. Remove mud and other dirt promptly so it does not dry and then turn into dust. Techniques that can be used for unpaved roads and lots include: Lower speed limits. High vehicle speed increases the amount of dust stirred up from unpaved roads and lots. Upgrade the road surface strength by improving particle size, shape, and mineral types that make up the surface and base materials. Add surface gravel to reduce the source of dust emission. Limit the amount of fine particles (those smaller than .075 mm) to 10 to 20 percent. Use geotextile fabrics to increase the strength of new roads or roads undergoing reconstruction. Encourage the use of alternate, paved routes, if available. Apply chemical dust suppressants using the admix method, blending the product with the top few inches of surface material. Suppressants may also be applied as surface treatments. Limit dust-causing work on windy days. Pave unpaved permanent roads and other trafficked areas. Maintenance Standards Respray area as necessary to keep dust to a minimum. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C150: Materials on Hand https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/2 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C150: Materials on Hand BMP C150: Materials on Hand Purpose Keep quantities of erosion prevention and sediment control materials on the project site at all times to be used for regular maintenance and emergency situations such as unexpected heavy rains. Having these materials on-site reduces the time needed to replace existing or implement new BMPs when inspections indicate that existing BMPs are not meeting the Construction SWPPP requirements. In addition, contractors can save money by buying some materials in bulk and storing them at their office or yard. Conditions of Use Construction projects of any size or type can benefit from having materials on hand. A small commercial development project could have a roll of plastic and some gravel available for immediate protection of bare soil and temporary berm construction. A large earthwork project, such as highway construction, might have several tons of straw, several rolls of plastic, flexible pipe, sandbags, geotextile fabric and steel “T” posts. Materials should be stockpiled and readily available before any site clearing, grubbing, or earthwork begins. A large contractor or project proponent could keep a stockpile of materials that are available for use on several projects. If storage space at the project site is at a premium, the contractor could maintain the materials at their office or yard. The office or yard must be less than an hour from the project site. Design and Installation Specifications Depending on project type, size, complexity, and length, materials and quantities will vary. A good minimum list of items that will cover numerous situations includes: Clear Plastic, 6 mil Drainpipe, 6 or 8 inch diameter Sandbags, filled Straw Bales for mulching Quarry Spalls Washed Gravel Geotextile Fabric 12/21/2020 BMP C150: Materials on Hand https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/2 Catch Basin Inserts Steel "T" Posts Silt fence material Straw Wattles Maintenance Standards All materials with the exception of the quarry spalls, steel “T” posts, and gravel should be kept covered and out of both sun and rain. Re-stock materials as needed. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C151: Concrete Handling https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/2 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C151: Concrete Handling BMP C151: Concrete Handling Purpose Concrete work can generate process water and slurry that contain fine particles and high pH, both of which can violate water quality standards in the receiving water. Concrete spillage or concrete discharge to waters of the State is prohibited. Use this BMP to minimize and eliminate concrete, concrete process water, and concrete slurry from entering waters of the State. Conditions of Use Any time concrete is used, utilize these management practices. Concrete construction project components include, but are not limited to: Curbs Sidewalks Roads Bridges Foundations Floors Runways Disposal options for concrete, in order of preference are: 1. Off-site disposal 2. Concrete wash-out areas (see BMP C154: Concrete Washout Area) 3. De minimus washout to formed areas awaiting concrete Design and Installation Specifications Wash concrete truck drums at an approved off-site location or in designated concrete washout areas only. Do not wash out concrete trucks onto the ground (including formed areas awaiting concrete), or into storm drains, open ditches, streets, or streams. Refer to BMP C154: Concrete Washout Area for information on concrete washout areas. 12/21/2020 BMP C151: Concrete Handling https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/2 Return unused concrete remaining in the truck and pump to the originating batch plant for recycling. Do not dump excess concrete on site, except in designated concrete washout areas as allowed in BMP C154: Concrete Washout Area. Wash small concrete handling equipment (e.g. hand tools, screeds, shovels, rakes, floats, trowels, and wheelbarrows) into designated concrete washout areas or into formed areas awaiting concrete pour. At no time shall concrete be washed off into the footprint of an area where an infiltration feature will be installed. Wash equipment difficult to move, such as concrete paving machines, in areas that do not directly drain to natural or constructed stormwater conveyance or potential infiltration areas. Do not allow washwater from areas, such as concrete aggregate driveways, to drain directly (without detention or treatment) to natural or constructed stormwater conveyances. Contain washwater and leftover product in a lined container when no designated concrete washout areas (or formed areas, allowed as described above) are available. Dispose of contained concrete and concrete washwater (process water) properly. Always use forms or solid barriers for concrete pours, such as pilings, within 15-feet of surface waters. Refer to BMP C252: Treating and Disposing of High pH Water for pH adjustment requirements. Refer to the Construction Stormwater General Permit (CSWGP) for pH monitoring requirements if the project involves one of the following activities: Significant concrete work (as defined in the CSWGP). The use of soils amended with (but not limited to) Portland cement-treated base, cement kiln dust or fly ash. Discharging stormwater to segments of water bodies on the 303(d) list (Category 5) for high pH. Maintenance Standards Check containers for holes in the liner daily during concrete pours and repair the same day. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C152: Sawcutting and Surfacing Pollution Prevention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/2 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C152: Sawcutting and Surfacing Pollution Prevention BMP C152: Sawcutting and Surfacing Pollution Prevention Purpose Sawcutting and surfacing operations generate slurry and process water that contains fine particles and high pH (concrete cutting), both of which can violate the water quality standards in the receiving water. Concrete spillage or concrete discharge to waters of the State is prohibited. Use this BMP to minimize and eliminate process water and slurry created through sawcutting or surfacing from entering waters of the State. Conditions of Use Utilize these management practices anytime sawcutting or surfacing operations take place. Sawcutting and surfacing operations include, but are not limited to: Sawing Coring Grinding Roughening Hydro-demolition Bridge and road surfacing Design and Installation Specifications Vacuum slurry and cuttings during cutting and surfacing operations. Slurry and cuttings shall not remain on permanent concrete or asphalt pavement overnight. Slurry and cuttings shall not drain to any natural or constructed drainage conveyance including stormwater systems. This may require temporarily blocking catch basins. Dispose of collected slurry and cuttings in a manner that does not violate ground water or surface water quality standards. Do not allow process water generated during hydro-demolition, surface roughening or similar operations to drain to any natural or constructed drainage conveyance including stormwater systems. Dispose of process water in a manner that does not violate ground water or surface water quality standards. 12/21/2020 BMP C152: Sawcutting and Surfacing Pollution Prevention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/2 Handle and dispose of cleaning waste material and demolition debris in a manner that does not cause contamination of water. Dispose of sweeping material from a pick-up sweeper at an appropriate disposal site. Maintenance Standards Continually monitor operations to determine whether slurry, cuttings, or process water could enter waters of the state. If inspections show that a violation of water quality standards could occur, stop operations and immediately implement preventive measures such as berms, barriers, secondary containment, and/or vacuum trucks. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C153: Material Delivery, Storage, and Containment https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/3 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C153: Material Delivery, Storage, and Containment BMP C153: Material Delivery, Storage, and Containment Purpose Prevent, reduce, or eliminate the discharge of pollutants to the stormwater system or watercourses from material delivery and storage. Minimize the storage of hazardous materials on-site, store materials in a designated area, and install secondary containment. Conditions of Use Use at construction sites with delivery and storage of the following materials: Petroleum products such as fuel, oil and grease Soil stabilizers and binders (e.g., Polyacrylamide) Fertilizers, pesticides and herbicides Detergents Asphalt and concrete compounds Hazardous chemicals such as acids, lime, adhesives, paints, solvents, and curing compounds Any other material that may be detrimental if released to the environment Design and Installation Specifications The temporary storage area should be located away from vehicular traffic, near the construction entrance(s), and away from waterways or storm drains. Safety Data Sheets (SDS) should be supplied for all materials stored. Chemicals should be kept in their original labeled containers. Hazardous material storage on-site should be minimized. Hazardous materials should be handled as infrequently as possible. During the wet weather season (Oct 1 – April 30), consider storing materials in a covered area. Materials should be stored in secondary containments, such as an earthen dike, horse trough, or even a children’s wading pool for non-reactive materials such as detergents, oil, grease, and paints. Small amounts of material may be secondarily contained in “bus boy” trays or concrete mixing trays. 12/21/2020 BMP C153: Material Delivery, Storage, and Containment https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/3 Do not store chemicals, drums, or bagged materials directly on the ground. Place these items on a pallet and, when possible, within secondary containment. If drums must be kept uncovered, store them at a slight angle to reduce ponding of rainwater on the lids to reduce corrosion. Domed plastic covers are inexpensive and snap to the top of drums, preventing water from collecting. Liquids, petroleum products, and substances listed in 40 CFR Parts 110, 117, or 302 shall be stored in approved containers and drums and shall not be overfilled. Containers and drums shall be stored in temporary secondary containment facilities. Temporary secondary containment facilities shall provide for a spill containment volume able to contain 10% of the total enclosed container volume of all containers, or 110% of the capacity of the largest container within its boundary, whichever is greater. Secondary containment facilities shall be impervious to the materials stored therein for a minimum contact time of 72 hours. Sufficient separation should be provided between stored containers to allow for spill cleanup and emergency response access. During the wet weather season (Oct 1 – April 30), each secondary containment facility shall be covered during non-working days, prior to and during rain events. Keep material storage areas clean, organized and equipped with an ample supply of appropriate spill clean- up material (spill kit). The spill kit should include, at a minimum: 1-Water Resistant Nylon Bag 3-Oil Absorbent Socks 3”x 4’ 2-Oil Absorbent Socks 3”x 10’ 12-Oil Absorbent Pads 17”x19” 1-Pair Splash Resistant Goggles 3-Pair Nitrile Gloves 10-Disposable Bags with Ties Instructions Maintenance Standards Secondary containment facilities shall be maintained free of accumulated rainwater and spills. In the event of spills or leaks, accumulated rainwater and spills shall be collected and placed into drums. These liquids 12/21/2020 BMP C153: Material Delivery, Storage, and Containment https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…3/3 shall be handled as hazardous waste unless testing determines them to be non-hazardous. Re-stock spill kit materials as needed. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C154: Concrete Washout Area https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/5 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C154: Concrete Washout Area BMP C154: Concrete Washout Area Purpose Prevent or reduce the discharge of pollutants from concrete waste to stormwater by conducting washout off-site, or performing on-site washout in a designated area. Conditions of Use Concrete washout areas are implemented on construction projects where: Concrete is used as a construction material It is not possible to dispose of all concrete wastewater and washout off-site (ready mix plant, etc.). Concrete truck drums are washed on-site. Note that auxiliary concrete truck components (e.g. chutes and hoses) and small concrete handling equipment (e.g. hand tools, screeds, shovels, rakes, floats, trowels, and wheelbarrows) may be washed into formed areas awaiting concrete pour. At no time shall concrete be washed off into the footprint of an area where an infiltration feature will be installed. Design and Installation Specifications Implementation Perform washout of concrete truck drums at an approved off-site location or in designated concrete washout areas only. Do not wash out concrete onto non-formed areas, or into storm drains, open ditches, streets, or streams. Wash equipment difficult to move, such as concrete paving machines, in areas that do not directly drain to natural or constructed stormwater conveyance or potential infiltration areas. Do not allow excess concrete to be dumped on-site, except in designated concrete washout areas as allowed above. Concrete washout areas may be prefabricated concrete washout containers, or self-installed structures (above-grade or below-grade). Prefabricated containers are most resistant to damage and protect against spills and leaks. Companies may offer delivery service and provide regular maintenance and disposal of solid and liquid waste. 12/21/2020 BMP C154: Concrete Washout Area https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/5 If self-installed concrete washout areas are used, below-grade structures are preferred over above-grade structures because they are less prone to spills and leaks. Self-installed above-grade structures should only be used if excavation is not practical. Concrete washout areas shall be constructed and maintained in sufficient quantity and size to contain all liquid and concrete waste generated by washout operations. Education Discuss the concrete management techniques described in this BMP with the ready-mix concrete supplier before any deliveries are made. Educate employees and subcontractors on the concrete waste management techniques described in this BMP. Arrange for the contractor’s superintendent or Certified Erosion and Sediment Control Lead (CESCL) to oversee and enforce concrete waste management procedures. A sign should be installed adjacent to each concrete washout area to inform concrete equipment operators to utilize the proper facilities. Contracts Incorporate requirements for concrete waste management into concrete supplier and subcontractor agreements. Location and Placement Locate concrete washout areas at least 50 feet from sensitive areas such as storm drains, open ditches, water bodies, or wetlands. Allow convenient access to the concrete washout area for concrete trucks, preferably near the area where the concrete is being poured. If trucks need to leave a paved area to access the concrete washout area, prevent track-out with a pad of rock or quarry spalls (see BMP C105: Stabilized Construction Access). These areas should be far enough away from other construction traffic to reduce the likelihood of accidental damage and spills. The number of concrete washout areas you install should depend on the expected demand for storage capacity. On large sites with extensive concrete work, concrete washout areas should be placed in multiple locations for ease of use by concrete truck drivers. Concrete Truck Washout Procedures Washout of concrete truck drums shall be performed in designated concrete washout areas only. 12/21/2020 BMP C154: Concrete Washout Area https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…3/5 Concrete washout from concrete pumper bins can be washed into concrete pumper trucks and discharged into designated concrete washout areas or properly disposed of off-site. Concrete Washout Area Installation Concrete washout areas should be constructed as shown in the figures below, with a recommended minimum length and minimum width of 10 ft, but with sufficient quantity and volume to contain all liquid and concrete waste generated by washout operations. Plastic lining material should be a minimum of 10 mil polyethylene sheeting and should be free of holes, tears, or other defects that compromise the impermeability of the material. Lath and flagging should be commercial type. Liner seams shall be installed in accordance with manufacturers’ recommendations. Soil base shall be prepared free of rocks or other debris that may cause tears or holes in the plastic lining material. Maintenance Standards Inspection and Maintenance Inspect and verify that concrete washout areas are in place prior to the commencement of concrete work. Once concrete wastes are washed into the designated washout area and allowed to harden, the concrete should be broken up, removed, and disposed of per applicable solid waste regulations. Dispose of hardened concrete on a regular basis. During periods of concrete work, inspect the concrete washout areas daily to verify continued performance. Check overall condition and performance. Check remaining capacity (% full). If using self-installed concrete washout areas, verify plastic liners are intact and sidewalls are not damaged. If using prefabricated containers, check for leaks. Maintain the concrete washout areas to provide adequate holding capacity with a minimum freeboard of 12 inches. Concrete washout areas must be cleaned, or new concrete washout areas must be constructed and ready for use once the concrete washout area is 75% full. If the concrete washout area is nearing capacity, vacuum and dispose of the waste material in an approved manner. 12/21/2020 BMP C154: Concrete Washout Area https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…4/5 Do not discharge liquid or slurry to waterways, storm drains or directly onto ground. Do not discharge to the sanitary sewer without local approval. Place a secure, non-collapsing, non-water collecting cover over the concrete washout area prior to predicted wet weather to prevent accumulation and overflow of precipitation. Remove and dispose of hardened concrete and return the structure to a functional condition. Concrete may be reused on-site or hauled away for disposal or recycling. When you remove materials from a self-installed concrete washout area, build a new structure; or, if the previous structure is still intact, inspect for signs of weakening or damage, and make any necessary repairs. Re-line the structure with new plastic after each cleaning. Removal of Concrete Washout Areas When concrete washout areas are no longer required for the work, the hardened concrete, slurries and liquids shall be removed and properly disposed of. Materials used to construct concrete washout areas shall be removed from the site of the work and disposed of or recycled. Holes, depressions or other ground disturbance caused by the removal of the concrete washout areas shall be backfilled, repaired, and stabilized to prevent erosion. Figure II-3.7: Concrete Washout Area with Wood Planks pdf download Figure II-3.8: Concrete Washout Area with Straw Bales pdf download Figure II-3.9: Prefabricated Concrete Washout Container w/Ramp 12/21/2020 BMP C154: Concrete Washout Area https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…5/5 pdf download Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C160: Certified Erosion and Sediment Control Lead https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/2 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C160: Certified Erosion and Sediment Control Lead BMP C160: Certified Erosion and Sediment Control Lead Purpose The project proponent designates at least one person as the responsible representative in charge of erosion and sediment control (ESC), and water quality protection. The designated person shall be responsible for ensuring compliance with all local, state, and federal erosion and sediment control and water quality requirements. Construction sites one acre or larger that discharge to waters of the State must designate a Certified Erosion and Sediment Control Lead (CESCL) as the responsible representative. Conditions of Use A CESCL shall be made available on projects one acre or larger that discharge stormwater to surface waters of the state. Sites less than one acre may have a person without CESCL certification conduct inspections. The CESCL shall: Have a current certificate proving attendance in an erosion and sediment control training course that meets the minimum ESC training and certification requirements established by Ecology. Ecology has provided the minimum requirements for CESCL course training, as well as a list of ESC training and certification providers at: https://ecology.wa.gov/Regulations-Permits/Permits-certifications/Certified-erosion-sediment-control OR Be a Certified Professional in Erosion and Sediment Control (CPESC). For additional information go to: http://www.envirocertintl.org/cpesc/ Specifications CESCL certification shall remain valid for three years. The CESCL shall have authority to act on behalf of the contractor or project proponent and shall be available, or on-call, 24 hours per day throughout the period of construction. The Construction SWPPP shall include the name, telephone number, fax number, and address of the designated CESCL. See II-2 Construction Stormwater Pollution Prevention Plans (Construction SWPPPs). A CESCL may provide inspection and compliance services for multiple construction projects in the same geographic region, but must be on site whenever earthwork activities are occurring that could generate 12/21/2020 BMP C160: Certified Erosion and Sediment Control Lead https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/2 release of turbid water. Duties and responsibilities of the CESCL shall include, but are not limited to the following: Maintaining a permit file on site at all times which includes the Construction SWPPP and any associated permits and plans. Directing BMP installation, inspection, maintenance, modification, and removal. Updating all project drawings and the Construction SWPPP with changes made. Completing any sampling requirements including reporting results using electronic Discharge Monitoring Reports (WebDMR). Facilitate, participate in, and take corrective actions resulting from inspections performed by outside agencies or the owner. Keeping daily logs, and inspection reports. Inspection reports should include: Inspection date/time. Weather information; general conditions during inspection and approximate amount of precipitation since the last inspection. Visual monitoring results, including a description of discharged stormwater. The presence of suspended sediment, turbid water, discoloration, and oil sheen shall be noted, as applicable. Any water quality monitoring performed during inspection. General comments and notes, including a brief description of any BMP repairs, maintenance or installations made as a result of the inspection. A summary or list of all BMPs implemented, including observations of all erosion/sediment control structures or practices. The following shall be noted: 1. Locations of BMPs inspected. 2. Locations of BMPs that need maintenance. 3. Locations of BMPs that failed to operate as designed or intended. 4. Locations of where additional or different BMPs are required. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C162: Scheduling https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/1 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C162: Scheduling BMP C162: Scheduling Purpose Sequencing a construction project reduces the amount and duration of soil exposed to erosion by wind, rain, runoff, and vehicle tracking. Conditions of Use The construction sequence schedule is an orderly listing of all major land-disturbing activities together with the necessary erosion and sedimentation control measures planned for the project. This type of schedule guides the contractor on work to be done before other work is started so that serious erosion and sedimentation problems can be avoided. Following a specified work schedule that coordinates the timing of land-disturbing activities and the installation of control measures is perhaps the most cost-effective way of controlling erosion during construction. The removal of ground cover leaves a site vulnerable to erosion. Construction sequencing that limits land clearing, provides timely installation of erosion and sedimentation controls, and restores protective cover quickly can significantly reduce the erosion potential of a site. Design Considerations Minimize construction during rainy periods. Schedule projects to disturb only small portions of the site at any one time. Complete grading as soon as possible. Immediately stabilize the disturbed portion before grading the next portion. Practice staged seeding in order to revegetate cut and fill slopes as the work progresses. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C220: Inlet Protection https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/6 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C220: Inlet Protection BMP C220: Inlet Protection Purpose Inlet protection prevents coarse sediment from entering drainage systems prior to permanent stabilization of the disturbed area. Conditions of Use Use inlet protection at inlets that are operational before permanent stabilization of the disturbed areas that contribute runoff to the inlet. Provide protection for all storm drain inlets downslope and within 500 feet of a disturbed or construction area, unless those inlets are preceded by a sediment trapping BMP. Also consider inlet protection for lawn and yard drains on new home construction. These small and numerous drains coupled with lack of gutters can add significant amounts of sediment into the roof drain system. If possible, delay installing lawn and yard drains until just before landscaping, or cap these drains to prevent sediment from entering the system until completion of landscaping. Provide 18-inches of sod around each finished lawn and yard drain. Table II-3.10: Storm Drain Inlet Protection lists several options for inlet protection. All of the methods for inlet protection tend to plug and require a high frequency of maintenance. Limit contributing drainage areas for an individual inlet to one acre or less. If possible, provide emergency overflows with additional end-of-pipe treatment where stormwater ponding would cause a hazard. Table II-3.10: Storm Drain Inlet Protection Type of Inlet Protection Emergency Overflow Applicable for Paved/ Earthen Surfaces Conditions of Use Drop Inlet Protection Excavated drop inlet protection Yes, temporary flooding may occur Earthen Applicable for heavy flows. Easy to maintain. Large area requirement: 30'x30'/acre Block and gravel drop inlet protection Yes Paved or Earthen Applicable for heavy concentrated flows. Will not pond. Gravel and wire drop inlet protection No Paved or Earthen Applicable for heavy concentrated flows. Will pond. Can withstand traffic. Catch basin filters Yes Paved or Earthen Frequent maintenance required. Curb Inlet Protection 12/21/2020 BMP C220: Inlet Protection https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/6 Type of Inlet Protection Emergency Overflow Applicable for Paved/ Earthen Surfaces Conditions of Use Curb inlet protection with wooden weir Small capacity overflow Paved Used for sturdy, more compact installation. Block and gravel curb inlet protection Yes Paved Sturdy, but limited filtration. Culvert Inlet Protection Culvert inlet sediment trap N/A N/A 18 month expected life. Design and Installation Specifications Excavated Drop Inlet Protection Excavated drop inlet protection consists of an excavated impoundment around the storm drain inlet. Sediment settles out of the stormwater prior to entering the storm drain. Design and installation specifications for excavated drop inlet protection include: Provide a depth of 1-2 ft as measured from the crest of the inlet structure. Slope sides of excavation should be no steeper than 2H:1V. Minimum volume of excavation is 35 cubic yards. Shape the excavation to fit the site, with the longest dimension oriented toward the longest inflow area. Install provisions for draining to prevent standing water. Clear the area of all debris. Grade the approach to the inlet uniformly. Drill weep holes into the side of the inlet. Protect weep holes with screen wire and washed aggregate. Seal weep holes when removing structure and stabilizing area. Build a temporary dike, if necessary, to the down slope side of the structure to prevent bypass flow. Block and Gravel Filter A block and gravel filter is a barrier formed around the inlet with standard concrete blocks and gravel. See Figure II-3.17: Block and Gravel Filter. Design and installation specifications for block gravel filters include: 12/21/2020 BMP C220: Inlet Protection https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…3/6 Provide a height of 1 to 2 feet above the inlet. Recess the first row of blocks 2-inches into the ground for stability. Support subsequent courses by placing a pressure treated wood 2x4 through the block opening. Do not use mortar. Lay some blocks in the bottom row on their side to allow for dewatering the pool. Place hardware cloth or comparable wire mesh with ½-inch openings over all block openings. Place gravel to just below the top of blocks on slopes of 2H:1V or flatter. An alternative design is a gravel berm surrounding the inlet, as follows: Provide a slope of 3H:1V on the upstream side of the berm. Provide a slope of 2H:1V on the downstream side of the berm. Provide a 1-foot wide level stone area between the gravel berm and the inlet. Use stones 3 inches in diameter or larger on the upstream slope of the berm. Use gravel ½- to ¾-inch at a minimum thickness of 1-foot on the downstream slope of the berm. Figure II-3.17: Block and Gravel Filter pdf download Gravel and Wire Mesh Filter Gravel and wire mesh filters are gravel barriers placed over the top of the inlet. This method does not provide an overflow. Design and installation specifications for gravel and wire mesh filters include: Use a hardware cloth or comparable wire mesh with ½-inch openings. Place wire mesh over the drop inlet so that the wire extends a minimum of 1-foot beyond each side of the inlet structure. Overlap the strips if more than one strip of mesh is necessary. Place coarse aggregate over the wire mesh. Provide at least a 12-inch depth of aggregate over the entire inlet opening and extend at least 18- inches on all sides. 12/21/2020 BMP C220: Inlet Protection https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…4/6 Catch Basin Filters Catch basin filters are designed by manufacturers for construction sites. The limited sediment storage capacity increases the amount of inspection and maintenance required, which may be daily for heavy sediment loads. To reduce maintenance requirements, combine a catch basin filter with another type of inlet protection. This type of inlet protection provides flow bypass without overflow and therefore may be a better method for inlets located along active rights-of-way. Design and installation specifications for catch basin filters include: Provides 5 cubic feet of storage. Requires dewatering provisions. Provides a high-flow bypass that will not clog under normal use at a construction site. Insert the catch basin filter in the catch basin just below the grating. Curb Inlet Protection with Wooden Weir Curb inlet protection with wooden weir is an option that consists of a barrier formed around a curb inlet with a wooden frame and gravel. Design and installation specifications for curb inlet protection with wooden weirs include: Use wire mesh with ½-inch openings. Use extra strength filter cloth. Construct a frame. Attach the wire and filter fabric to the frame. Pile coarse washed aggregate against the wire and fabric. Place weight on the frame anchors. Block and Gravel Curb Inlet Protection Block and gravel curb inlet protection is a barrier formed around a curb inlet with concrete blocks and gravel. See Figure II-3.18: Block and Gravel Curb Inlet Protection. Design and installation specifications for block and gravel curb inlet protection include: Use wire mesh with ½-inch openings. Place two concrete blocks on their sides abutting the curb at either side of the inlet opening. These are spacer blocks. Place a 2x4 stud through the outer holes of each spacer block to align the front blocks. Place blocks on their sides across the front of the inlet and abutting the spacer blocks. 12/21/2020 BMP C220: Inlet Protection https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…5/6 Place wire mesh over the outside vertical face. Pile coarse aggregate against the wire to the top of the barrier. Figure II-3.18: Block and Gravel Curb Inlet Protection pdf download Curb and Gutter Sediment Barrier Curb and gutter sediment barrier is a sandbag or rock berm (riprap and aggregate) 3 feet high and 3 feet wide in a horseshoe shape. See Figure II-3.19: Curb and Gutter Barrier. Design and installation specifications for curb and gutter sediment barrier include: Construct a horseshoe shaped berm, faced with coarse aggregate if using riprap, 3 feet high and 3 feet wide, at least 2 feet from the inlet. Construct a horseshoe shaped sedimentation trap on the upstream side of the berm. Size the trap to sediment trap standards for protecting a culvert inlet. Figure II-3.19: Curb and Gutter Barrier pdf download Maintenance Standards Inspect all forms of inlet protection frequently, especially after storm events. Clean and replace clogged catch basin filters. For rock and gravel filters, pull away the rocks from the inlet and clean or replace. An alternative approach would be to use the clogged rock as fill and put fresh rock around the inlet. Do not wash sediment into storm drains while cleaning. Spread all excavated material evenly over the surrounding land area or stockpile and stabilize as appropriate. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did not pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions may choose not to accept 12/21/2020 BMP C220: Inlet Protection https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…6/6 these products, or may require additional testing prior to consideration for local use. Products that Ecology has approved as functionally equivalent are available for review on Ecology’s website at: https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-permittee-guidance- resources/Emerging-stormwater-treatment-technologies Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C233: Silt Fence https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/5 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C233: Silt Fence BMP C233: Silt Fence Purpose Silt fence reduces the transport of coarse sediment from a construction site by providing a temporary physical barrier to sediment and reducing the runoff velocities of overland flow. Conditions of Use Silt fence may be used downslope of all disturbed areas. Silt fence shall prevent sediment carried by runoff from going beneath, through, or over the top of the silt fence, but shall allow the water to pass through the fence. Silt fence is not intended to treat concentrated flows, nor is it intended to treat substantial amounts of overland flow. Convey any concentrated flows through the drainage system to a sediment trapping BMP. Do not construct silt fences in streams or use in V-shaped ditches. Silt fences do not provide an adequate method of silt control for anything deeper than sheet or overland flow. Figure II-3.22: Silt Fence pdf download Design and Installation Specifications Use in combination with other construction stormwater BMPs. Maximum slope steepness (perpendicular to the silt fence line) 1H:1V. Maximum sheet or overland flow path length to the silt fence of 100 feet. Do not allow flows greater than 0.5 cfs. Use geotextile fabric that meets the following standards. All geotextile properties listed below are minimum average roll values (i.e., the test result for any sampled roll in a lot shall meet or exceed the values shown in Table II-3.11: Geotextile Fabric Standards for Silt Fence): 12/21/2020 BMP C233: Silt Fence https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/5 Table II-3.11: Geotextile Fabric Standards for Silt Fence Geotextile Property Minimum Average Roll Value Polymeric Mesh AOS (ASTM D4751) 0.60 mm maximum for slit film woven (#30 sieve). 0.30 mm maximum for all other geotextile types (#50 sieve). 0.15 mm minimum for all fabric types (#100 sieve). Water Permittivity (ASTM D4491)0.02 sec-1 minimum Grab Tensile Strength (ASTM D4632) 180 lbs. Minimum for extra strength fabric. 100 lbs minimum for standard strength fabric. Grab Tensile Strength (ASTM D4632)30% maximum Ultraviolet Resistance (ASTM D4355)70% minimum Support standard strength geotextiles with wire mesh, chicken wire, 2-inch x 2-inch wire, safety fence, or jute mesh to increase the strength of the geotextile. Silt fence materials are available that have synthetic mesh backing attached. Silt fence material shall contain ultraviolet ray inhibitors and stabilizers to provide a minimum of six months of expected usable construction life at a temperature range of 0°F to 120°F. One-hundred percent biodegradable silt fence is available that is strong, long lasting, and can be left in place after the project is completed, if permitted by the local jurisdiction. Refer to Figure II-3.22: Silt Fence for standard silt fence details. Include the following Standard Notes for silt fence on construction plans and specifications: 1. The Contractor shall install and maintain temporary silt fences at the locations shown in the Plans. 2. Construct silt fences in areas of clearing, grading, or drainage prior to starting those activities. 3. The silt fence shall have a 2-feet min. and a 2½-feet max. height above the original ground surface. 4. The geotextile fabric shall be sewn together at the point of manufacture to form fabric lengths as required. Locate all sewn seams at support posts. Alternatively, two sections of silt fence can be overlapped, provided that the overlap is long enough and that the adjacent silt fence sections are close enough together to prevent silt laden water from escaping through the fence at the overlap. 12/21/2020 BMP C233: Silt Fence https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…3/5 5. Attach the geotextile fabric on the up-slope side of the posts and secure with staples, wire, or in accordance with the manufacturer's recommendations. Attach the geotextile fabric to the posts in a manner that reduces the potential for tearing. 6. Support the geotextile fabric with wire or plastic mesh, dependent on the properties of the geotextile selected for use. If wire or plastic mesh is used, fasten the mesh securely to the up- slope side of the posts with the geotextile fabric up-slope of the mesh. 7. Mesh support, if used, shall consist of steel wire with a maximum mesh spacing of 2-inches, or a prefabricated polymeric mesh. The strength of the wire or polymeric mesh shall be equivalent to or greater than 180 lbs. grab tensile strength. The polymeric mesh must be as resistant to the same level of ultraviolet radiation as the geotextile fabric it supports. 8. Bury the bottom of the geotextile fabric 4-inches min. below the ground surface. Backfill and tamp soil in place over the buried portion of the geotextile fabric, so that no flow can pass beneath the silt fence and scouring cannot occur. When wire or polymeric back-up support mesh is used, the wire or polymeric mesh shall extend into the ground 3-inches min. 9. Drive or place the silt fence posts into the ground 18-inches min. A 12–inch min. depth is allowed if topsoil or other soft subgrade soil is not present and 18-inches cannot be reached. Increase fence post min. depths by 6 inches if the fence is located on slopes of 3H:1V or steeper and the slope is perpendicular to the fence. If required post depths cannot be obtained, the posts shall be adequately secured by bracing or guying to prevent overturning of the fence due to sediment loading. 10. Use wood, steel or equivalent posts. The spacing of the support posts shall be a maximum of 6-feet. Posts shall consist of either: Wood with minimum dimensions of 2 inches by 2 inches by 3 feet. Wood shall be free of defects such as knots, splits, or gouges. No. 6 steel rebar or larger. ASTM A 120 steel pipe with a minimum diameter of 1-inch. U, T, L, or C shape steel posts with a minimum weight of 1.35 lbs./ft. Other steel posts having equivalent strength and bending resistance to the post sizes listed above. 11. Locate silt fences on contour as much as possible, except at the ends of the fence, where the fence shall be turned uphill such that the silt fence captures the runoff water and prevents water from flowing around the end of the fence. 12. If the fence must cross contours, with the exception of the ends of the fence, place check dams perpendicular to the back of the fence to minimize concentrated flow and erosion. The slope of the fence line where contours must be crossed shall not be steeper than 3H:1V. 12/21/2020 BMP C233: Silt Fence https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…4/5 Check dams shall be approximately 1-foot deep at the back of the fence. Check dams shall be continued perpendicular to the fence at the same elevation until the top of the check dam intercepts the ground surface behind the fence. Check dams shall consist of crushed surfacing base course, gravel backfill for walls, or shoulder ballast. Check dams shall be located every 10 feet along the fence where the fence must cross contours. Refer to Figure II-3.23: Silt Fence Installation by Slicing Method for slicing method details. The following are specifications for silt fence installation using the slicing method: 1. The base of both end posts must be at least 2- to 4-inches above the top of the geotextile fabric on the middle posts for ditch checks to drain properly. Use a hand level or string level, if necessary, to mark base points before installation. 2. Install posts 3- to 4-feet apart in critical retention areas and 6- to 7-feet apart in standard applications. 3. Install posts 24-inches deep on the downstream side of the silt fence, and as close as possible to the geotextile fabric, enabling posts to support the geotextile fabric from upstream water pressure. 4. Install posts with the nipples facing away from the geotextile fabric. 5. Attach the geotextile fabric to each post with three ties, all spaced within the top 8-inches of the fabric. Attach each tie diagonally 45 degrees through the fabric, with each puncture at least 1- inch vertically apart. Each tie should be positioned to hang on a post nipple when tightening to prevent sagging. 6. Wrap approximately 6-inches of the geotextile fabric around the end posts and secure with 3 ties. 7. No more than 24-inches of a 36-inch geotextile fabric is allowed above ground level. 8. Compact the soil immediately next to the geotextile fabric with the front wheel of the tractor, skid steer, or roller exerting at least 60 pounds per square inch. Compact the upstream side first and then each side twice for a total of four trips. Check and correct the silt fence installation for any deviation before compaction. Use a flat-bladed shovel to tuck the fabric deeper into the ground if necessary. Figure II-3.23: Silt Fence Installation by Slicing Method pdf download 12/21/2020 BMP C233: Silt Fence https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…5/5 Maintenance Standards Repair any damage immediately. Intercept and convey all evident concentrated flows uphill of the silt fence to a sediment trapping BMP. Check the uphill side of the silt fence for signs of the fence clogging and acting as a barrier to flow and then causing channelization of flows parallel to the fence. If this occurs, replace the fence and remove the trapped sediment. Remove sediment deposits when the deposit reaches approximately one-third the height of the silt fence, or install a second silt fence. Replace geotextile fabric that has deteriorated due to ultraviolet breakdown. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C235: Wattles https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/2 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C235: Wattles BMP C235: Wattles Purpose Wattles are temporary erosion and sediment control barriers consisting of straw, compost, or other material that is wrapped in netting made of natural plant fiber or similar encasing material. They reduce the velocity and can spread the flow of rill and sheet runoff, and can capture and retain sediment. Conditions of Use Wattles shall consist of cylinders of plant material such as weed-free straw, coir, wood chips, excelsior, or wood fiber or shavings encased within netting made of natural plant fibers unaltered by synthetic materials. Use wattles: In disturbed areas that require immediate erosion protection. On exposed soils during the period of short construction delays, or over winter months. On slopes requiring stabilization until permanent vegetation can be established. The material used dictates the effectiveness period of the wattle. Generally, wattles are effective for one to two seasons. Prevent rilling beneath wattles by entrenching and overlapping wattles to prevent water from passing between them. Design Criteria See Figure II-3.24: Wattles for typical construction details. Wattles are typically 8 to 10 inches in diameter and 25 to 30 feet in length. Install wattles perpendicular to the flow direction and parallel to the slope contour. Place wattles in shallow trenches, staked along the contour of disturbed or newly constructed slopes. Dig narrow trenches across the slope (on contour) to a depth of 3- to 5-inches on clay soils and soils with gradual slopes. On loose soils, steep slopes, and areas with high rainfall, the trenches should be dug to a depth of 5- to 7- inches, or 1/2 to 2/3 of the thickness of the wattle. Start building trenches and installing wattles from the base of the slope and work up. Spread excavated material evenly along the uphill slope and compact it using hand tamping or other methods. 12/21/2020 BMP C235: Wattles https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/2 Construct trenches at intervals of 10- to 25-feet depending on the steepness of the slope, soil type, and rainfall. The steeper the slope the closer together the trenches. Install the wattles snugly into the trenches and overlap the ends of adjacent wattles 12 inches behind one another. Install stakes at each end of the wattle, and at 4-foot centers along entire length of wattle. If required, install pilot holes for the stakes using a straight bar to drive holes through the wattle and into the soil. Wooden stakes should be approximately 0.75 x 0.75 x 24 inches min. Willow cuttings or 3/8-inch rebar can also be used for stakes. Stakes should be driven through the middle of the wattle, leaving 2 to 3 inches of the stake protruding above the wattle. Figure II-3.24: Wattles pdf download Maintenance Standards Wattles may require maintenance to ensure they are in contact with soil and thoroughly entrenched, especially after significant rainfall on steep sandy soils. Inspect the slope after significant storms and repair any areas where wattles are not tightly abutted or water has scoured beneath the wattles. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did not pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jurisdictions may choose not to accept these products, or may require additional testing prior to consideration for local use. Products that Ecology has approved as functionally equivalent are available for review on Ecology’s website at: https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-permittee-guidance- resources/Emerging-stormwater-treatment-technologies Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C250: Construction Stormwater Chemical Treatment https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/9 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C250: Construction Stormwater Chemical Treatment BMP C250: Construction Stormwater Chemical Treatment Purpose This BMP applies when using chemicals to treat turbidity in stormwater by either batch or flow-through chemical treatment. Turbidity is difficult to control once fine particles are suspended in stormwater runoff from a construction site. BMP C241: Sediment Pond (Temporary) is effective at removing larger particulate matter by gravity settling, but is ineffective at removing smaller particulates such as clay and fine silt. Traditional Construction Stormwater BMPs may not be adequate to ensure compliance with the water quality standards for turbidity in the receiving water. Chemical treatment can reliably provide exceptional reductions of turbidity and associated pollutants. Chemical treatment may be required to meet turbidity stormwater discharge requirements, especially when construction proceeds through the wet season. Conditions of Use Formal written approval from Ecology is required for the use of chemical treatment, regardless of site size. See https://fortress.wa.gov/ecy/publications/SummaryPages/ecy070258.html for a copy of the Request for Chemical Treatment form. The Local Permitting Authority may also require review and approval. When authorized, the chemical treatment systems must be included in the Construction Stormwater Pollution Prevention Plan (SWPPP). Chemically treated stormwater discharged from construction sites must be nontoxic to aquatic organisms. The Chemical Technology Assessment Protocol - Ecology (CTAPE) must be used to evaluate chemicals proposed for stormwater treatment. Only chemicals approved by Ecology under the CTAPE may be used for stormwater treatment. The approved chemicals, their allowable application techniques (batch treatment or flow-through treatment), allowable application rates, and conditions of use can be found at the Department of Ecology Emerging Technologies website: https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-permittee-guidance- resources/Emerging-stormwater-treatment-technologies Background on Chemical Treatment Systems Coagulation and flocculation have been used for over a century to treat water. The use of coagulation and flocculation to treat stormwater is a very recent application. Experience with the treatment of water and wastewater has resulted in a basic understanding of the process, in particular factors that affect performance. This experience can provide insights as to how to most effectively design and operate similar systems in the treatment of stormwater. 12/21/2020 BMP C250: Construction Stormwater Chemical Treatment https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/9 Fine particles suspended in water give it a milky appearance, measured as turbidity. Their small size, often much less than 1 µm in diameter, give them a very large surface area relative to their volume. These fine particles typically carry a negative surface charge. Largely because of these two factors (small size and negative charge), these particles tend to stay in suspension for extended periods of time. Thus, removal is not practical by gravity settling. These are called stable suspensions. Chemicals like polymers, as well as inorganic chemicals such as alum, speed the settling process. The added chemical destabilizes the suspension and causes the smaller particles to flocculate. The process consists of three primary steps: coagulation, flocculation, and settling or clarification. Ecology requires a fourth step, filtration, on all stormwater chemical treatment systems to reduce floc discharge and to provide monitoring prior to discharge. General Design and Installation Specifications Chemicals approved for use in Washington State are listed on Ecology's TAPE website, http://www.ecy.wa.gov/programs/wq/stormwater/newtech/technologies.html, under the "Construction" tab. Care must be taken in the design of the withdrawal system to minimize outflow velocities and to prevent floc discharge. Stormwater that has been chemically treated must be filtered through BMP C251: Construction Stormwater Filtration for filtration and monitoring prior to discharge. System discharge rates must take into account downstream conveyance integrity. The following equipment should be located on site in a lockable shed: The chemical injector. Secondary containment for acid, caustic, buffering compound, and treatment chemical. Emergency shower and eyewash. Monitoring equipment which consists of a pH meter and a turbidimeter. There are two types of systems for applying the chemical treatment process to stormwater: the batch chemical treatment system and the flow-through chemical treatment system. See below for further details for both types of systems. Batch Chemical Treatment Systems A batch chemical treatment system consists of four steps: coagulation, flocculation, clarification, and polishing and monitoring via filtration. Step 1: Coagulation Coagulation is the process by which negative charges on the fine particles are disrupted. By disrupting the negative charges, the fine particles are able to flocculate. Chemical addition is one method of destabilizing the suspension, and polymers are one class of chemicals that are generally effective. Chemicals that are used for this purpose are called coagulants. Coagulation is complete when the suspension is destabilized by the neutralization of the negative charges. Coagulants perform best when they are thoroughly and evenly dispersed under relatively 12/21/2020 BMP C250: Construction Stormwater Chemical Treatment https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…3/9 intense mixing. This rapid mixing involves adding the coagulant in a manner that promotes rapid dispersion, followed by a short time period for destabilization of the particle suspension. The particles are still very small and are not readily separated by clarification until flocculation occurs. Step 2: Flocculation Flocculation is the process by which fine particles that have been destabilized bind together to form larger particles that settle rapidly. Flocculation begins naturally following coagulation, but is enhanced by gentle mixing of the destabilized suspension. Gentle mixing helps to bring particles in contact with one another such that they bind and continually grow to form "flocs." As the size of the flocs increase, they become heavier and settle. Step 3: Clarification The final step is the settling of the particles, or clarification. Particle density, size and shape are important during settling. Dense, compact flocs settle more readily than less dense, fluffy flocs. Because of this, flocculation to form dense, compact flocs is particularly important during chemical treatment. Water temperature is important during settling. Both the density and viscosity of water are affected by temperature; these in turn affect settling. Cold temperatures increase viscosity and density, thus slowing down the rate at which the particles settle. The conditions under which clarification is achieved can affect performance. Currents can affect settling. Currents can be produced by wind, by differences between the temperature of the incoming water and the water in the clarifier, and by flow conditions near the inlets and outlets. Quiescent water, such as that which occurs during batch clarification, provides a good environment for settling. One source of currents in batch chemical treatment systems is movement of the water leaving the clarifier unit. Because flocs are relatively small and light, the velocity of the water must be as low as possible. Settled flocs can be resuspended and removed by fairly modest currents. Step 4: Filtration After clarification, Ecology requires stormwater that has been chemically treated to be filtered and monitored prior to discharge. The sand filtration system continually monitors the stormwater effluent for turbidity and pH. If the discharge water is ever out of an acceptable range for turbidity or pH, the water is returned to the untreated stormwater pond where it will begin the treatment process again. Design and Installation of Batch Chemical Treatment Systems A batch chemical treatment system consists of a stormwater collection system (either a temporary diversion or the permanent site drainage system), an untreated stormwater storage pond, pumps, a chemical feed system, treatment cells, a filtering and monitoring system, and interconnecting piping. The batch treatment system uses a storage pond for untreated stormwater, followed by a minimum of two lined treatment cells. Multiple treatment cells allow for clarification of chemically treated water in one cell, while other cells are being filled or emptied. Treatment cells may be ponds or tanks. Ponds with constructed earthen embankments greater than six feet high or which impound more than 10 acre-feet are subject to the Washington Dam Safety Regulations (Chapter 173-175 WAC). See BMP D.1: Detention Ponds for more information regarding dam safety considerations for ponds. 12/21/2020 BMP C250: Construction Stormwater Chemical Treatment https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…4/9 Stormwater is collected at interception point(s) on the site and is diverted by gravity or by pumping to an untreated stormwater storage pond or other untreated stormwater holding area. The stormwater is stored until treatment occurs. It is important that the storage pond is large enough to provide adequate storage. The first step in the treatment sequence is to check the pH of the stormwater in the untreated stormwater storage pond. The pH is adjusted by the application of carbon dioxide or a base until the stormwater in the untreated storage pond is within the desired pH range, 6.5 to 8.5. When used, carbon dioxide is added immediately downstream of the transfer pump. Typically sodium bicarbonate (baking soda) is used as a base, although other bases may be used. When needed, base is added directly to the untreated stormwater storage pond. The stormwater is recirculated with the treatment pump to provide mixing in the storage pond. Initial pH adjustments should be based on daily bench tests. Further pH adjustments can be made at any point in the process. See BMP C252: Treating and Disposing of High pH Water for more information on pH adjustments as a part of chemical treatment. Once the stormwater is within the desired pH range (which is dependant on the coagulant being used), the stormwater is pumped from the untreated stormwater storage pond to a lined treatment cell as a coagulant is added. The coagulant is added upstream of the pump to facilitate rapid mixing. The water is kept in the lined treatment cell for clarification. In a batch mode process, clarification typically takes from 30 minutes to several hours. Prior to discharge, samples are withdrawn for analysis of pH, coagulant concentration, and turbidity. If these levels are acceptable, the treated water is withdrawn, filtered, and discharged. Several configurations have been developed to withdraw treated water from the treatment cell. The original configuration is a device that withdraws the treated water from just beneath the water surface using a float with adjustable struts that prevent the float from settling on the cell bottom. This reduces the possibility of picking up floc from the bottom of the cell. The struts are usually set at a minimum clearance of about 12 inches; that is, the float will come within 12 inches of the bottom of the cell. Other systems have used vertical guides or cables which constrain the float, allowing it to drift up and down with the water level. More recent designs have an H-shaped array of pipes, set on the horizontal.This scheme provides for withdrawal from four points rather than one. This configuration reduces the likelihood of sucking settled solids from the bottom. It also reduces the tendency for a vortex to form. Inlet diffusers, a long floating or fixed pipe with many small holes in it, are also an option. Safety is a primary concern. Design should consider the hazards associated with operations, such as sampling. Facilities should be designed to reduce slip hazards and drowning. Tanks and ponds should have life rings, ladders, or steps extending from the bottom to the top. Sizing Batch Chemical Treatment Systems Chemical treatment systems must be designed to control the velocity and peak volumetric flow rate that is discharged from the system and consequently the project site. See Element 3: Control Flow Rates for further details on this requirement. The total volume of the untreated stormwater storage pond and treatment cells must be large enough to treat stormwater that is produced during multiple day storm events. It is recommended that at a minimum the untreated stormwater storage pond be sized to hold 1.5 times the volume of runoff generated from the site during the 10- 12/21/2020 BMP C250: Construction Stormwater Chemical Treatment https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…5/9 year, 24-hour storm event. Bypass should be provided around the chemical treatment system to accommodate extreme storm events. Runoff volume shall be calculated using the methods presented in III-2.3 Single Event Hydrograph Method. Worst-case land cover conditions (i.e., producing the most runoff) should be used for analyses (in most cases, this would be the land cover conditions just prior to final landscaping). Primary settling should be encouraged in the untreated stormwater storage pond. A forebay with access for maintenance may be beneficial. There are two opposing considerations in sizing the treatment cells. A larger cell is able to treat a larger volume of water each time a batch is processed. However, the larger the cell, the longer the time required to empty the cell. A larger cell may also be less effective at flocculation and therefore require a longer settling time. The simplest approach to sizing the treatment cell is to multiply the allowable discharge flow rate (as determined by the guidance in Element 3: Control Flow Rates) times the desired drawdown time. A 4-hour drawdown time allows one batch per cell per 8-hour work period, given 1 hour of flocculation followed by two hours of settling. See BMP C251: Construction Stormwater Filtration for details on sizing the filtration system at the end of the batch chemical treatment system. If the chemical treatment system design does not allow you to discharge at the rates as required by Element 3: Control Flow Rates, and if the site has a permanent Flow Control BMP that will serve the planned development, the discharge from the chemical treatment system may be directed to the permanent Flow Control BMP to comply with Element 3: Control Flow Rates. In this case, all discharge (including water passing through the treatment system and stormwater bypassing the treatment system) will be directed into the permanent Flow Control BMP. If site constraints make locating the untreated stormwater storage pond difficult, the permanent Flow Control BMP may be divided to serve as the untreated stormwater storage pond and the post-treatment temporary flow control pond. A berm or barrier must be used in this case so the untreated water does not mix with the treated water. Both untreated stormwater storage requirements, and adequate post-treatment flow control must be achieved. The designer must document in the Construction SWPPP how the permanent Flow Control BMP is able to attenuate the discharge from the site to meet the requirements of Element 3: Control Flow Rates. If the design of the permanent Flow Control BMP was modified for temporary construction flow control purposes, the construction of the permanent Flow Control BMP must be finalized, as designed for its permanent function, at project completion. Flow-Through Chemical Treatment Systems Background on Flow-Through Chemical Treatment Systems A flow-through chemical treatment system adds a sand filtration component to the batch chemical treatment system's treatment train following flocculation. The coagulant is added to the stormwater upstream of the sand filter so that the coagulation and flocculation step occur immediately prior to the filter. The advantage of a flow- through chemical treatment system is the time saved by immediately filtering the water, as opposed to waiting for the clarification process necessary in a batch chemical treatment system. See BMP C251: Construction Stormwater Filtration for more information on filtration. Design and Installation of Flow-Through Chemical Treatment Systems 12/21/2020 BMP C250: Construction Stormwater Chemical Treatment https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…6/9 At a minimum, a flow-through chemical treatment system consists of a stormwater collection system (either a temporary diversion or the permanent site drainage system), an untreated stormwater storage pond, and a chemically enhanced sand filtration system. As with a batch treatment system, stormwater is collected at interception point(s) on the site and is diverted by gravity or by pumping to an untreated stormwater storage pond or other untreated stormwater holding area. The stormwater is stored until treatment occurs. It is important that the holding pond be large enough to provide adequate storage. Stormwater is then pumped from the untreated stormwater storage pond to the chemically enhanced sand filtration system where a coagulant is added. Adjustments to pH may be necessary before coagulant addition. The sand filtration system continually monitors the stormwater effluent for turbidity and pH. If the discharge water is ever out of an acceptable range for turbidity or pH, the water is returned to the untreated stormwater pond where it will begin the treatment process again. Sizing Flow-Through Chemical Treatment Systems Refer to BMP C251: Construction Stormwater Filtration for sizing requirements of flow-through chemical treatment systems. Factors Affecting the Chemical Treatment Process Coagulants Cationic polymers can be used as coagulants to destabilize negatively charged turbidity particles present in natural waters, wastewater and stormwater. Polymers are large organic molecules that are made up of subunits linked together in a chain-like structure. Attached to these chain-like structures are other groups that carry positive or negative charges, or have no charge. Polymers that carry groups with positive charges are called cationic, those with negative charges are called anionic, and those with no charge (neutral) are called nonionic. In practice, the only way to determine whether a polymer is effective for a specific application is to perform preliminary or on- site testing. Aluminum sulfate (alum) can also be used as a coagulant, as this chemical becomes positively charged when dispersed in water. Polymers are available as powders, concentrated liquids, and emulsions (which appear as milky liquids). The latter are petroleum based, which are not allowed for construction stormwater treatment. Polymer effectiveness can degrade with time and also from other influences. Thus, manufacturers' recommendations for storage should be followed. Manufacturer’s recommendations usually do not provide assurance of water quality protection or safety to aquatic organisms. Consideration of water quality protection is necessary in the selection and use of all polymers. Application 12/21/2020 BMP C250: Construction Stormwater Chemical Treatment https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…7/9 Application of coagulants at the appropriate concentration or dosage rate for optimum turbidity removal is important for management of chemical cost, for effective performance, and to avoid aquatic toxicity. The optimum dose in a given application depends on several site-specific features. Turbidity of untreated water can be important with turbidities greater than 5,000 NTU. The surface charge of particles to be removed is also important. Environmental factors that can influence dosage rate are water temperature, pH, and the presence of constituents that consume or otherwise affect coagulant effectiveness. Laboratory experiments indicate that mixing previously settled sediment (floc sludge) with the untreated stormwater significantly improves clarification, therefore reducing the effective dosage rate. Preparation of working solutions and thorough dispersal of coagulants in water to be treated is also important to establish the appropriate dosage rate. For a given water sample, there is generally an optimum dosage rate that yields the lowest residual turbidity after settling. When dosage rates below this optimum value (underdosing) are applied, there is an insufficient quantity of coagulant to react with, and therefore destabilize, all of the turbidity present. The result is residual turbidity (after flocculation and settling) that is higher than with the optimum dose. Overdosing, application of dosage rates greater than the optimum value, can also negatively impact performance. Like underdosing, the result of overdosing is higher residual turbidity than that with the optimum dose. Mixing The G-value, or just "G", is often used as a measure of the mixing intensity applied during coagulation and flocculation. The symbol G stands for “velocity gradient”, which is related in part to the degree of turbulence generated during mixing. High G-values mean high turbulence, and vice versa. High G-values provide the best conditions for coagulant addition. With high G's, turbulence is high and coagulants are rapidly dispersed to their appropriate concentrations for effective destabilization of particle suspensions. Low G-values provide the best conditions for flocculation. Here, the goal is to promote formation of dense, compact flocs that will settle readily. Low G's provide low turbulence to promote particle collisions so that flocs can form. Low G's generate sufficient turbulence such that collisions are effective in floc formation, but do not break up flocs that have already formed. pH Adjustment The pH must be in the proper range for the coagulants to be effective, which is typically 6.5 to 8.5. As polymers tend to lower the pH, it is important that the stormwater have sufficient buffering capacity. Buffering capacity is a function of alkalinity. Without sufficient alkalinity, the application of the polymer may lower the pH to below 6.5. A pH below 6.5 not only reduces the effectiveness of the polymer as a coagulant, but it may also create a toxic condition for aquatic organisms. Stormwater may not be discharged without readjustment of the pH to above 6.5. The target pH should be within 0.2 standard units of the receiving water's pH. Experience gained at several projects in the City of Redmond has shown that the alkalinity needs to be at least 50 mg/L to prevent a drop in pH to below 6.5 when the polymer is added. Maintenance Standards 12/21/2020 BMP C250: Construction Stormwater Chemical Treatment https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…8/9 Monitoring At a minimum, the following monitoring shall be conducted. Test results shall be recorded on a daily log kept on site. Additional testing may be required by the NPDES permit based on site conditions. Operational Monitoring Total volume treated and discharged. Flow must be continuously monitored and recorded at not greater than 15-minute intervals. Type and amount of chemical used for pH adjustment. Type and amount of coagulant used for treatment. Settling time. Compliance Monitoring Influent and effluent pH, flocculent chemical concentration, and turbidity must be continuously monitored and recorded at not greater than 15-minute intervals. pH and turbidity of the receiving water. Biomonitoring Treated stormwater must be non-toxic to aquatic organisms. Treated stormwater must be tested for aquatic toxicity or residual chemicals. Frequency of biomonitoring will be determined by Ecology. Residual chemical tests must be approved by Ecology prior to their use. If testing treated stormwater for aquatic toxicity, you must test for acute (lethal) toxicity. Bioassays shall be conducted by a laboratory accredited by Ecology, unless otherwise approved by Ecology. Acute toxicity tests shall be conducted per the CTAPE protocol and Appendix G of Whole Effluent Toxicity Testing Guidance and Test Review Criteria (Marshall, 2016). Discharge Compliance Prior to discharge, treated stormwater must be sampled and tested for compliance with pH, flocculent chemical concentration, and turbidity limits. These limits may be established by the Construction Stormwater General Permit or a site-specific discharge permit. Sampling and testing for other pollutants may also be necessary at some sites. pH must be within the range of 6.5 to 8.5 standard units and not cause a change in the pH of the receiving water by more than 0.2 standard units. Treated stormwater samples and measurements shall be taken from the discharge pipe or another location representative of the nature of the treated stormwater discharge. Samples used for determining compliance with the water quality standards in the receiving water shall not be taken from the treatment pond prior to decanting. Compliance with the water quality standards is determined in the receiving water. 12/21/2020 BMP C250: Construction Stormwater Chemical Treatment https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…9/9 Operator Training Each project site using chemical treatment must have a trained operator who is certified for operation of an Enhanced Chemical Treatment system. The operator must be trained and certified by an organization approved by Ecology. Organizations approved for operator training are found at the following website: https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-permittee-guidance- resources/Contaminated-water-on-construction-sites Sediment Removal and Disposal Sediment shall be removed from the untreated stormwater storage pond and treatment cells as necessary. Typically, sediment removal is required at least once during a wet season and at the decommissioning of the chemical treatment system. Sediment remaining in the cells between batches may enhance the settling process and reduce the required chemical dosage. Sediment that is known to be non-toxic may be incorporated into the site away from drainages. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP C251: Construction Stormwater Filtration https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…1/3 You are here: 2019 SWMMWW > Volume II - Construction Stormwater Pollution Prevention > II-3 Construction Stormwater BMPs > BMP C251: Construction Stormwater Filtration BMP C251: Construction Stormwater Filtration Purpose Filtration removes sediment from runoff originating from disturbed areas of the site. Conditions of Use Traditional Construction Stormwater BMPs used to control soil erosion and sediment loss from construction sites may not be adequate to ensure compliance with the water quality standard for turbidity in the receiving water. Filtration may be used in conjunction with gravity settling to remove sediment as small as fine silt (0.5 µm). The reduction in turbidity will be dependent on the particle size distribution of the sediment in the stormwater. In some circumstances, sedimentation and filtration may achieve compliance with the water quality standard for turbidity. The use of construction stormwater filtration does not require approval from Ecology as long as treatment chemicals are not used. Filtration in conjunction with BMP C250: Construction Stormwater Chemical Treatment requires testing under the Chemical Technology Assessment Protocol – Ecology (CTAPE) before it can be initiated. Approval from Ecology must be obtained at each site where chemical use is proposed prior to use. See https://fortress.wa.gov/ecy/publications/SummaryPages/ecy070258.html for a copy of the Request for Chemical Treatment form. Design and Installation Specifications Two types of filtration systems may be applied to construction stormwater treatment: rapid and slow. Rapid filtration systems are the typical system used for water and wastewater treatment. They can achieve relatively high hydraulic flow rates, on the order of 2 to 20 gpm/sf, because they have automatic backwash systems to remove accumulated solids. Slow filtration systems have very low hydraulic rates, on the order of 0.02 gpm/sf, because they do not have backwash systems. Slow filtration systems have generally been used as post construction BMPs to treat stormwater (see V-6 Filtration BMPs). Slow filtration is mechanically simple in comparison to rapid filtration, but requires a much larger filter area. Filter Types and Efficiencies Sand media filters are available with automatic backwashing features that can filter to 50 µm particle size. Screen or bag filters can filter down to 5 µm. Fiber wound filters can remove particles down to 0.5 µm. Filters should be sequenced from the largest to the smallest pore opening. Sediment removal efficiency will be related to particle size distribution in the stormwater. 12/21/2020 BMP C251: Construction Stormwater Filtration https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…2/3 Treatment Process and Description Stormwater is collected at interception point(s) on the site and diverted to an untreated stormwater sediment pond or tank for removal of large sediment, and storage of the stormwater before it is treated by the filtration system. In a rapid filtration system, the untreated stormwater is pumped from the pond or tank through the filtration media. Slow filtration systems are designed using gravity to convey water from the pond or tank to and through the filtration media. Sizing Filtration treatment systems must be designed to control the velocity and peak volumetric flow rate that is discharged from the system and consequently the project site. See Element 3: Control Flow Rates for further details on this requirement. The untreated stormwater storage pond or tank should be sized to hold 1.5 times the volume of runoff generated from the site during the 10-year, 24-hour storm event, minus the filtration treatment system flowrate for an 8-hour period. For a chitosan-enhanced sand filtration system, the filtration treatment system flowrate should be sized using a hydraulic loading rate between 6-8 gpm/ft2. Other hydraulic loading rates may be more appropriate for other systems. Bypass should be provided around the filtration treatment system to accommodate extreme storm events. Runoff volume shall be calculated using the methods presented in III-2.3 Single Event Hydrograph Method. Worst-case land cover conditions (i.e., producing the most runoff) should be used for analyses (in most cases, this would be the land cover conditions just prior to final landscaping). If the filtration treatment system design does not allow you to discharge at the rates as required by Element 3: Control Flow Rates, and if the site has a permanent Flow Control BMP that will serve the planned development, the discharge from the filtration treatment system may be directed to the permanent Flow Control BMP to comply with Element 3: Control Flow Rates. In this case, all discharge (including water passing through the treatment system and stormwater bypassing the treatment system) will be directed into the permanent Flow Control BMP. If site constraints make locating the untreated stormwater storage pond difficult, the permanent Flow Control BMP may be divided to serve as the untreated stormwater storage pond and the post-treatment temporary flow control pond. A berm or barrier must be used in this case so the untreated water does not mix with the treated water. Both untreated stormwater storage requirements, and adequate post-treatment flow control must be achieved. The designer must document in the Construction SWPPP how the permanent Flow Control BMP is able to attenuate the discharge from the site to meet the requirements of Element 3: Control Flow Rates. If the design of the permanent Flow Control BMP was modified for temporary construction flow control purposes, the construction of the permanent Flow Control BMP must be finalized, as designed for its permanent function, at project completion. Maintenance Standards Rapid sand filters typically have automatic backwash systems that are triggered by a pre-set pressure drop across the filter. If the backwash water volume is not large or substantially more turbid than the untreated stormwater stored in the holding pond or tank, backwash return to the untreated stormwater pond or tank may be appropriate. However, other means of treatment and disposal may be necessary. Screen, bag, and fiber filters must be cleaned and/or replaced when they become clogged. 12/21/2020 BMP C251: Construction Stormwater Filtration https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeII/ConstructionStormwaterBMPs/Constructi…3/3 Sediment shall be removed from the storage and/or treatment ponds as necessary. Typically, sediment removal is required once or twice during a wet season and at the decommissioning of the ponds. Disposal of filtration equipment must comply with applicable local, state, and federal regulations. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 ATTACHMENT F Source Control BMPs 12/21/2020 S408 BMPs for Dust Control at Manufacturing Areas https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/SoilErosionSedimentControlAndLandsc…1/2 You are here: 2019 SWMMWW > Volume IV - Source Control BMP Library > IV-4 Soil Erosion, Sediment Control, and Landscaping Source Control BMPs > S408 BMPs for Dust Control at Manufacturing Areas S408 BMPs for Dust Control at Manufacturing Areas Note: Contact the local air quality authority for appropriate and required BMPs for dust control to implement at your project site. Use the following website to determine the air quality authority for the project site: https://ecology.wa.gov/About-us/Our-role-in-the-community/Partnerships-committees/Clean-air-agencies Description of Pollutant Sources: Industrial material handling activities can generate considerable amounts of dust that is typically removed using exhaust systems. Mixing cement and concrete products and handling powdered materials can also generate dust. Particulate materials that can cause air pollution include grain dust, sawdust, coal, gravel, crushed rock, cement, and boiler fly ash. Air emissions can contaminate stormwater. The objective of this BMP is to reduce the stormwater pollutants caused by dust generation and control. Pollutant Control Approach: Prevent dust generation and emissions where feasible, regularly clean-up dust that can contaminate stormwater, and convey dust contaminated stormwater to proper treatment. Applicable BMPs: Clean, as needed, powder material handling equipment and vehicles. Regularly sweep dust accumulation areas that can contaminate stormwater. Conduct sweeping using vacuum filter equipment to minimize dust generation and to ensure optimal dust removal. Use dust filtration/collection systems such as baghouse filters, cyclone separators, etc. to control vented dust emissions that could contaminate stormwater. Control of zinc dusts in rubber production is one example. Maintain on-site controls to prevent vehicle track-out. Maintain dust collection devices on a regular basis. Recommended BMPs: In manufacturing operations, train employees to handle powders carefully to prevent generation of dust. Use water spray to flush dust accumulations to sanitary sewers where allowed by the local sewer authority or to other appropriate treatment system. Use approved dust suppressants such as those listed in Methods for Dust Control (Ecology, 2016b). Application of some products may not be appropriate in close proximity to receiving waters or conveyances close to receiving waters. For more information check with Ecology or the local jurisdiction. Recommended Treatment BMPs 12/21/2020 S410 BMPs for Correcting Illicit Discharges to Storm Drains https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/SourceControlBMPsApplicableToAllSite…2/2 During non-stormwater conditions, inspect each storm drain for non-stormwater discharges. Record the locations of all non-stormwater discharges. Include all permitted discharges. If useful, prepare a map of each area. Show on the map the known location of storm sewers, sanitary sewers, and permitted and unpermitted discharges. Aerial photos may be useful. Check records such as piping schematics to identify known side sewer connections and show these on the map. Consider using smoke, dye, or chemical analysis tests to detect connections between two conveyance systems (e.g., process water and stormwater). If desirable, conduct TV inspections of the storm drains and record the footage on videotape. Compare the observed locations of connections with the information on the map and revise the map accordingly. Note suspect connections that are inconsistent with the field survey. Identify all connections to storm sewers or to surface water and take the actions specified above as applicable BMPs. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 S411 BMPs for Landscaping and Lawn / Vegetation Management https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/SoilErosionSedimentControlAndLandsc…1/4 You are here: 2019 SWMMWW > Volume IV - Source Control BMP Library > IV-4 Soil Erosion, Sediment Control, and Landscaping Source Control BMPs > S411 BMPs for Landscaping and Lawn / Vegetation Management S411 BMPs for Landscaping and Lawn / Vegetation Management Description of Pollutant Sources: Landscaping can include grading, soil transfer, vegetation planting, and vegetation removal. Examples include weed control on golf course lawns, access roads, and utility corridors and during landscaping; and residential lawn/plant care. Proper management of vegetation can minimize excess nutrients and pesticides. Pollutant Control Approach: Maintain appropriate vegetation to control erosion and the discharge of stormwater pollutants. Prevent debris contamination of stormwater. Where practicable, grow plant species appropriate for the site, or adjust the soil properties of the site to grow desired plant species. Applicable BMPs: Install engineered soil/landscape systems to improve the infiltration and regulation of stormwater in landscaped areas. Select the right plants for the planting location based on proposed use, available maintenance,soil conditions, sun exposure, water availability, height, sight factors, and space available. Ensure that plants selected for planting are not on the noxious weed list. For example, butterfly bush often gets planted as an ornamental but is actually on the noxious weed list. The Washington State Noxious Weed List can be found at the following webpage: https://www.nwcb.wa.gov/printable-noxious-weed-list Do not dispose of collected vegetation into waterways or storm sewer systems. Do not blow vegetation or other debris into the drainage system. Dispose of collected vegetation such as grass clippings, leaves, sticks by composting or recycling. Remove, bag, and dispose of class A & B noxious weeds in the garbage immediately. Do not compost noxious weeds as it may lead to spreading through seed or fragment if the composting process is not hot enough. Use manual and/or mechanical methods of vegetation removal (pincer-type weeding tools, flame weeders, or hot water weeders as appropriate) rather than applying herbicides, where practical. Use at least an eight-inch "topsoil" layer with at least 8 percent organic matter to provide a sufficient vegetation-growing medium. Organic matter is the least water-soluble form of nutrients that can be added to the soil. Composted organic matter generally releases only between 2 and 10 percent of its total nitrogen annually, and this release corresponds closely to the plant growth cycle. Return natural plant debris and mulch to the soil, to continue recycling nutrients indefinitely. Select the appropriate turfgrass mixture for the climate and soil type. Certain tall fescues and rye grasses resist insect attack because the symbiotic endophytic fungi found naturally in their tissues repel or kill common leaf and stem-eating lawn insects. 12/21/2020 S411 BMPs for Landscaping and Lawn / Vegetation Management https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/SoilErosionSedimentControlAndLandsc…2/4 The fungus causes no known adverse effects to the host plant or to humans. Tall fescues and rye grasses do not repel root-feeding lawn pests such as Crane Fly larvae. Tall fescues and rye grasses are toxic to ruminants such as cattle and sheep Endophytic grasses are commercially available; use them in areas such as parks or golf courses where grazing does not occur. Local agricultural or gardening resources such as Washington State University Extension office can offer advice on which types of grass are best suited to the area and soil type. Use the following seeding and planting BMPs, or equivalent BMPs, to obtain information on grass mixtures, temporary and permanent seeding procedures, maintenance of a recently planted area, and fertilizer application rates: BMP C120: Temporary and Permanent Seeding, BMP C121: Mulching, BMP C123: Plastic Covering, and BMP C124: Sodding. Adjusting the soil properties of the subject site can assist in selection of desired plant species. Consult a soil restoration specialist for site-specific conditions. Recommended Additional BMPs: Conduct mulch-mowing whenever practicable. Use native plants in landscaping. Native plants do not require extensive fertilizer or pesticide applications. Native plants may also require less watering. Use mulch or other erosion control measures on soils exposed for more than one week during the dry season (May 1 to September 30) or two days during the rainy season (October 1 to April 30). Till a topsoil mix or composted organic material into the soil to create a well-mixed transition layer that encourages deeper root systems and drought-resistant plants. Apply an annual topdressing application of 3/8” compost. Amending existing landscapes and turf systems by increasing the percent organic matter and depth of topsoil can: Substantially improve the permeability of the soil. Increase the disease and drought resistance of the vegetation. Reduces the demand for fertilizers and pesticides. Disinfect gardening tools after pruning diseased plants to prevent the spread of disease. Prune trees and shrubs in a manner appropriate for each species. If specific plants have a high mortality rate, assess the cause and replace with another more appropriate species. When working around and below mature trees, follow the most current American National Standards Institute (ANSI) ANSI A300 standards (see http://www.tcia.org/TCIA/BUSINESS/ANSI_A300_Standards_/TCIA/BUSINESS/A300_Standards/A300_Standards.aspx? hkey=202ff566-4364-4686-b7c1-2a365af59669) and International Society of Arboriculture BMPs to the extent practicable (e.g., take care to minimize any damage to tree roots and avoid compaction of soil). Monitor tree support systems (stakes, guys, etc.). Repair and adjust as needed to provide support and prevent tree damage. 12/21/2020 S411 BMPs for Landscaping and Lawn / Vegetation Management https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/SoilErosionSedimentControlAndLandsc…3/4 Remove tree supports after one growing season or maximum of 1 year. Backfill stake holes after removal. When continued, regular pruning (more than one time during the growing season) is required to maintain visual sight lines for safety or clearance along a walk or drive, consider relocating the plant to a more appropriate location. Make reasonable attempts to remove and dispose of class C noxious weeds. Re-seed bare turf areas until the vegetation fully covers the ground surface. Watch for and respond to new occurrences of especially aggressive weeds such as Himalayan blackberry, Japanese knotweed, morning glory, English ivy, and reed canary grass to avoid invasions. Plant and protect trees per BMP T5.16: Tree Retention and Tree Planting. Aerate lawns regularly in areas of heavy use where the soil tends to become compacted. Conduct aeration while the grasses in the lawn are growing most vigorously. Remove layers of thatch greater than ¾-inch deep. Set the mowing height at the highest acceptable level and mow at times and intervals designed to minimize stress on the turf. Generally mowing only 1/3 of the grass blade height will prevent stressing the turf. Mowing is a stress-creating activity for turfgrass. Grass decreases its productivity when mowed too short and there is less growth of roots and rhizomes. The turf becomes less tolerant of environmental stresses, more disease prone and more reliant on outside means such as pesticides, fertilizers, and irrigation to remain healthy. Additional BMP Information: King County's Best Management Practices for Golf Course Development and Operation (King County, 1993) has additional BMPs for Turfgrass Maintenance and Operation. King County, Seattle Public Utilities, and the Saving Water Partnership have created the following natural lawn and garden care resources that include guidance on building healthy soil with compost and mulch, selecting appropriate plants, watering, using alternatives to pesticides, and implementing natural lawn care techniques. Natural Yard Care - Five steps to make your piece of the planet a healthier place to live (King County and SPU, 2008) The Natural Lawn & Garden Series: Smart Watering (Saving Water Partnership, 2006) Natural Lawn Care for Western Washington (Saving Water Partnership, 2007) The Natural Lawn & Garden Series: Growing Healthy Soil; Choosing the Right Plants; and Natural Pest, Weed and Disease Control (Saving Water Partnership, 2012) The International Society of Arboriculture (ISA) is a group that promotes the professional practice of arboriculture and fosters a greater worldwide awareness of the benefits of trees through research, technology, and education. ISA standards used for managing trees, shrubs, and other woody plants are the American National Standards Institute (ANSI) A300 standards. The ANSI A300 standards are voluntary industry consensus standards developed by the Tree Care Industry Association (TCIA) and written by the Accredited Standards Committee (ASC). The ANSI standards can be found on the ISA website: www.isa-arbor.com/education/publications/index.aspx 12/21/2020 S411 BMPs for Landscaping and Lawn / Vegetation Management https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/SoilErosionSedimentControlAndLandsc…4/4 Washington State University's Gardening in Washington State website at http://gardening.wsu.edu contains Washington State specific information about vegetation management based on the type of landscape. See the Pacific Northwest Plant Disease Management Handbook (Pscheidt and Ocamb, 2016) for information on disease recognition and for additional resources. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 S417 BMPs for Maintenance of Stormwater Drainage and Treatment Systems https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/RoadsDitchesAndParkingLotSourceCon…1/2 You are here: 2019 SWMMWW > Volume IV - Source Control BMP Library > IV-3 Roads, Ditches, and Parking Lot Source Control BMPs > S417 BMPs for Maintenance of Stormwater Drainage and Treatment Systems S417 BMPs for Maintenance of Stormwater Drainage and Treatment Systems Description of Pollutant Sources: Facilities include roadside catch basins on arterials and within residential areas, conveyance systems, detention facilities such as ponds and vaults, oil/water separators, biofilters, settling basins, infiltration systems, and all other types of stormwater treatment systems presented in Volume V. Oil and grease, hydrocarbons, debris, heavy metals, sediments and contaminated water are found in catch basins, oil and water separators, settling basins, etc. Pollutant Control Approach: Provide maintenance and cleaning of debris, sediments, and other pollutants from stormwater collection, conveyance, and treatment systems to maintain proper operation. Applicable Operational BMPs: Maintain stormwater treatment facilities per the operations and maintenance (O&M) procedures presented in Appendix V-A: BMP Maintenance Tables in addition to the following BMPs: Inspect and clean treatment BMPs, conveyance systems, and catch basins as needed, and determine necessary O&M improvements. Promptly repair any deterioration threatening the structural integrity of stormwater facilities. These include replacement of clean-out gates, catch basin lids, and rock in emergency spillways. Ensure adequacy of storm sewer capacities and prevent heavy sediment discharges to the sewer system. Regularly remove debris and sludge from BMPs used for peak-rate control, treatment, etc. and discharge to a sanitary sewer if approved by the sewer authority, or truck to an appropriate local or state government approved disposal site. Clean catch basins when the depth of deposits reaches 60 percent of the sump depth as measured from the bottom of basin to the invert of the lowest pipe into or out of the basin. However, in no case should there be less than six inches clearance from the debris surface to the invert of the lowest pipe. Some catch basins (for example, WSDOT's Catch Basin Type 1L (WSDOT, 2011)) may have as little as 12 inches sediment storage below the invert. These catch basins need frequent inspection and cleaning to prevent scouring. Where these catch basins are part of a stormwater collection and treatment system, the system owner/operator may choose to concentrate maintenance efforts on downstream control devices as part of a systems approach. Properly dispose of all solids, polluted material, and stagnant water collected through system cleaning. Do not decant water back into the drainage system from eductor trucks or vacuum equipment since there may be residual contaminants in the cleaning equipment. Do not jet material downstream into the public drainage system. 12/21/2020 S417 BMPs for Maintenance of Stormwater Drainage and Treatment Systems https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/RoadsDitchesAndParkingLotSourceCon…2/2 Clean woody debris in a catch basin as frequently as needed to ensure proper operation of the catch basin. Post warning signs; “Dump No Waste - Drains to Ground Water,” “Streams,” “Lakes,” or emboss on or adjacent to all storm drain inlets where possible. Disposal of sediments and liquids from the catch basins must comply with Appendix IV-B: Management of Street Waste Solids and Liquids. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 S421 BMPs for Parking and Storage of Vehicles and Equipment https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/RoadsDitchesAndParkingLotSourceCon…1/2 You are here: 2019 SWMMWW > Volume IV - Source Control BMP Library > IV-3 Roads, Ditches, and Parking Lot Source Control BMPs > S421 BMPs for Parking and Storage of Vehicles and Equipment S421 BMPs for Parking and Storage of Vehicles and Equipment Description of Pollutant Sources: Public and commercial parking lots such as retail store, fleet vehicle (including rent-a-car lots and car dealerships), equipment sale and rental parking lots, and parking lot driveways, can be sources of toxic hydrocarbons and other organic compounds, including oils and greases, metals, and suspended solids. Pollutant Control Approach: If the parking lot meets the site use thresholds to determine if the site is expected to generate high concentrations of oil, as defined in Step 2: Determine if an Oil Control BMP is Required in III-1.2 Choosing Your Runoff Treatment BMPs, provide oil removal equipment for the contaminated stormwater runoff. Applicable Operational BMPs: If a parking lot must be washed, discharge the washwater to a sanitary sewer, if allowed by the local sewer authority, or other approved wastewater treatment system, or collect washwater for off-site disposal. Do not hose down the area to a storm sewer or receiving water. Vacuum sweep parking lots, storage areas, and driveways regularly to collect dirt, waste, and debris. Mechanical or hand sweeping may be necessary for areas where a vacuum sweeper cannot reach. Clean up vehicle and equipment fluid drips and spills immediately. Place drip pans below leaking vehicles (including inoperative vehicles and equipment) in a manner that catches leaks or spills, including employee vehicles. Drip pans must be managed to prevent overfilling and the contents disposed of properly. Recommended Operational BMPs: Encourage employees to repair leaking personal vehicles. Encourage employees to carpool or use public transit through incentives. Encourage customers to use public transit by rewarding valid transit pass holders with discounts. Install catch basin inserts to collect excess sediment and oil if necessary. Inspect and maintain catch basin inserts to ensure they are working correctly. Applicable Treatment BMPs: Establishments subject to high-use intensity are significant sources of oil contamination of stormwater. Examples of potential high use areas include customer parking lots at fast food stores, grocery stores, taverns, restaurants, 12/21/2020 S421 BMPs for Parking and Storage of Vehicles and Equipment https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/RoadsDitchesAndParkingLotSourceCon…2/2 large shopping malls, discount warehouse stores, quick-lube shops, and banks. Refer to Step 2: Determine if an Oil Control BMP is Required in III-1.2 Choosing Your Runoff Treatment BMPs for the site use thresholds that determine if an oil control BMP is required, and for a list of oil control BMPs. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 S424 BMPs for Roof / Building Drains at Manufacturing and Commercial Buildings https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/OtherSourceControlBMPs/BMPs424.ht…1/2 You are here: 2019 SWMMWW > Volume IV - Source Control BMP Library > IV-7 Other Source Control BMPs > S424 BMPs for Roof / Building Drains at Manufacturing and Commercial Buildings S424 BMPs for Roof / Building Drains at Manufacturing and Commercial Buildings Description of Pollutant Sources: Stormwater runoff from roofs and sides of manufacturing and commercial buildings can be sources of pollutants caused by leaching of roofing materials, paints, caulking, building vents, and other air emission sources. Research has identified vapors and entrained liquid and solid droplets/particles as potential pollutants in roof/building runoff. Metals, solvents, acidic/alkaline pH, BOD, PCBs, and organics are some of the pollutant constituents identified. Ecology has performed a study on zinc in industrial stormwater. The study is presented in Suggested Practices to Reduce Zinc Concentrations in Industrial Stormwater Discharges (Ecology, 2008). The user should refer to this document for more details on addressing zinc in stormwater. Pollutant Control Approach: Evaluate the potential sources of stormwater pollutants and apply source control BMPs where feasible. Applicable Operational Source Control BMPs: If leachates and/or emissions from buildings are suspected sources of stormwater pollutants, then sample and analyze the stormwater draining from the building. Sweep the area routinely to remove any residual pollutants. If a roof/building stormwater pollutant source is identified, implement appropriate source control measures such as air pollution control equipment, selection of materials, operational changes, material recycle, process changes, etc. Applicable Structural Source Control BMPs: Paint/coat the galvanized surfaces as described in Suggested Practices to Reduce Zinc Concentrations in Industrial Stormwater Discharges (Ecology, 2008). Applicable Treatment BMPs: Treat runoff from roofs to the appropriate level. The facility may use Enhanced Treatment BMPs as described in III-1.2 Choosing Your Runoff Treatment BMPs. Some facilities regulated by the Industrial Stormwater General Permit, or local jurisdiction, may have requirements than cannot be achieved with Enhanced Treatment BMPs. In these cases, additional treatment measures may be required. A treatment method for meeting stringent requirements such as Chitosan-Enhanced Sand Filtration may be appropriate. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) 12/21/2020 S442 BMPs for Labeling Storm Drain Inlets On Your Property https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/OtherSourceControlBMPs/BMPs442.ht…1/2 You are here: 2019 SWMMWW > Volume IV - Source Control BMP Library > IV-7 Other Source Control BMPs > S442 BMPs for Labeling Storm Drain Inlets On Your Property S442 BMPs for Labeling Storm Drain Inlets On Your Property Description of Pollutant Sources: Waste materials dumped into storm drain inlets can have severe impacts on receiving waters. Posting notices regarding discharge prohibitions at storm drain inlets can prevent waste dumping. Storm drain signs and stencils are highly visible source controls that are typically placed directly adjacent to storm drain inlets. Pollutant Control Approach: The stencil, affixed sign, or metal grate contains a brief statement that prohibits dumping of improper materials into the urban runoff conveyance system. Storm drain messages have become a popular method of alerting the public about the effects of and the prohibitions against waste disposal. Applicable Operational BMPs: Label storm drain inlets in residential, commercial, industrial areas, and any other areas where contributions or dumping to storm drains is likely. Stencil or apply storm drain markers adjacent to storm drain inlets to help prevent the improper disposal of pollutants. Or, use a storm drain grate stamped with warnings against polluting. Place the marker in clear sight facing toward anyone approaching the inlet from either side. Use a brief statement and / or graphical icons to discourage illegal dumping. Examples include: “No Dumping – Drains to Stream” “No Pollutants – Drains to Puget Sound” “Dump No Waste – Drains to Lake” “No Dumping – Puget Sound Starts Here” Check with your local government agency to find out if they have approved specific signage and / or storm drain message placards for use. Consult the local agency stormwater staff to determine specific requirements for placard types and methods of application. Maintain the legibility of markers and signs. Signage on top of curbs tends to weather and fade. Signage on face of curbs tends to be worn by contact with vehicle tires and sweeper brooms. When painting stencils or installing markers, temporarily block the storm drain inlet so that no pollutants are discharged from the labeling activities. Optional Operational BMPs: Use a stencil in addition to a storm drain marker or grate to increase visibility of the message. 12/21/2020 S442 BMPs for Labeling Storm Drain Inlets On Your Property https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/OtherSourceControlBMPs/BMPs442.ht…2/2 Reference for this BMP: (CASQA, 2003) Figure IV-7.6: Storm Drain Inlet Labels pdf download Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 S447 BMPs for Roof Vents https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/OtherSourceControlBMPs/BMPs447.ht…1/2 You are here: 2019 SWMMWW > Volume IV - Source Control BMP Library > IV-7 Other Source Control BMPs > S447 BMPs for Roof Vents S447 BMPs for Roof Vents Description of Pollutant Sources: This activity applies to processes that vent emissions to the roof and/or the accumulation of pollutants on roofs. Processes of special concern are stone cutting, metal grinding, spray painting, paint stripping, galvanizing and electroplating. Pollutants from these processes may build up on roofs and may pollute stormwater roof runoff. Pollutant Control Approach: Evaluate the potential sources of stormwater pollutants and apply source control BMPs where feasible. Applicable BMPs: Identify processes that are vented and may contribute pollutants to the roof. Pollutants of concern include and are not limited to: Metal dust Grease from food preparation Solvents Hydrocarbons Fines Stone dust Look for chemical deposition around vents, pipes, and other surfaces. Install and maintain appropriate source control measures such as air pollution control equipment (filters, scrubbers, and other treatment). (City of San José Environmental Services, 2004) Check that your scrubber solution is appropriate for the chemistry of the fumes. Install vent covers and drip pans where there are none. Prevent leaks in pipefittings and containment vessels with routine maintenance. Consider instituting operational or process changes to reduce pollution. If proper installation and maintenance of air pollution control equipment does not prevent pollutant fallout on your roof, additional treatment of the roof runoff may be necessary. Install/provide appropriate devices for roof runoff before it is discharged off site. This may include approved water quality treatment BMPs or structural stormwater treatment systems. 12/21/2020 S447 BMPs for Roof Vents https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/OtherSourceControlBMPs/BMPs447.ht…2/2 Maintain air filters and pollution control equipment on a regular basis to ensure they are working properly. (The smell of odors from outside the building indicates that the pollution control equipment may need maintenance or evaluation.) When cleaning accumulated emissions from roof tops, collect the washwater and loose materials using a sump pump, wet vacuum or similar device. Discharge the collected runoff to the sanitary sewer after approval by the local sewer authority, or have a waste disposal company remove it. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 S450 BMPs for Irrigation https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/SoilErosionSedimentControlAndLandsc…1/2 You are here: 2019 SWMMWW > Volume IV - Source Control BMP Library > IV-4 Soil Erosion, Sediment Control, and Landscaping Source Control BMPs > S450 BMPs for Irrigation S450 BMPs for Irrigation Description of Pollutant Sources: Irrigation consists of discharges from irrigation water lines, landscape irrigation, and lawn or garden watering. Excessive watering can lead to discharges of chlorinated potable water runoff into drainage systems; it can also cause erosion; and negatively affect plant health. Improper irrigation can encourage pest problems, leach nutrients, and make a lawn completely dependent on artificial watering. Mosquito breeding habitats may form through excessive watering. Pollutant Control Approach: Limit the amount and location of watering to prevent runoff and discharges to drainage systems. Applicable Operational BMPs: Irrigate with the minimum amount of water needed. Never water at rates that exceed the infiltration rate of the soil. Maintain all irrigation systems so that irrigation water is applied evenly and where it is needed. Ensure sprinkler systems do not overspray vegetated areas resulting in excess water discharging into the drainage system. Inspect irrigated areas for excess watering. Adjust watering times and schedules to ensure that the appropriate amount of water is being used to minimize runoff. Consider factors such as soil structure, grade, time of year, and type of plant material in determining the proper amounts of water for a specific area. Inspect irrigated areas regularly for signs of erosion and / or discharge. Place sprinkler systems appropriately so that water is not being sprayed on impervious surfaces instead of vegetation. Repair broken or leaking sprinkler nozzles as soon as possible. Appropriately irrigate lawns based on the species planted, the available water holding capacity of the soil, and the efficiency of the irrigation system. The depth from which a plant normally extracts water depends on the rooting depth of the plant. Appropriately irrigated lawn grasses normally root in the top 6 to 12 inches of soil; lawns irrigated on a daily basis often root only in the top 1 inch of soil. Do not irrigate plants during or immediately after fertilizer application. The longer the period between fertilizer application and irrigation, the less fertilizer runoff occurs. Do not irrigate plants during or immediately after pesticide application (unless the pesticide label directs such timing). 12/21/2020 S450 BMPs for Irrigation https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/SoilErosionSedimentControlAndLandsc…2/2 Reduce frequency and / or intensity of watering as appropriate for the wet season (October 1 to April 30). Place irrigation systems to ensure that plants receive water where they need it. For example, do not place irrigation systems downgradient of plant’s root zones on hillsides. Recommended Operational BMPs: Add a tree bag or slow-release watering device (e.g., bucket with a perforated bottom) for watering newly installed trees when irrigation system is not present. Water deeply, but infrequently, so that the top 6 to 12 inches of the root zone is moist. Use soaker hoses or spot water with a shower type wand when an irrigation system is not present. Pulse water to enhance soil absorption, when feasible. Pre-moisten soil to break surface tension of dry or hydrophobic soils/mulch, followed by several more passes. With this method, each pass increases soil absorption and allows more water to infiltrate prior to runoff. Identify trigger mechanisms for drought-stress (e.g., leaf wilt, leaf senescence, etc.) of different species and water immediately after initial signs of stress appear. Water during drought conditions or more often if necessary to maintain plant cover. Adjust irrigation frequency / intensity as appropriate after plant establishment. Annually inspect irrigation systems to ensure: That there are no blockages of sprayer nozzles. Sprayer nozzles are rotating as appropriate. Sprayer systems are still aligned with the plant locations and root zones. Consult with the local water utility, Conservation District, or Cooperative Extension office to help determine optimum irrigation practices. Do not use chemigation and fertigation in irrigation systems. This will help avoid over application of pesticides and fertilizers. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 S453 BMPs for Formation of a Pollution Prevention Team https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/SourceControlBMPsApplicableToAllSite…1/1 You are here: 2019 SWMMWW > Volume IV - Source Control BMP Library > IV-1 Source Control BMPs Applicable to All Sites > S453 BMPs for Formation of a Pollution Prevention Team S453 BMPs for Formation of a Pollution Prevention Team The pollution prevention team should be responsible for implementing and maintaining all BMPs and treatment for the site. This team should be able to address any corrective actions needed on site to mitigate potential stormwater contamination. The team members should: Consist of those people who are familiar with the facility and its operations. Possess the knowledge and skills to assess conditions and activities that could impact stormwater quality at your facility, and who can evaluate the effectiveness of control measures. Assign pollution prevention team staff to be on duty on a daily basis to cover applicable permittee facilities when those facilities are in operation. Have the primary responsibility for developing and overseeing facility activities necessary to comply with stormwater requirements. Have access to all applicable permit, monitoring, SWPPP, and other records. Be trained in the operation, maintenance and inspections of all BMPs and reporting procedures. Establish responsibilities for inspections, operation, maintenance, and emergencies. Regularly meet to review overall facility operations and BMP effectiveness. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 S454 BMPs for Preventive Maintenance / Good Housekeeping https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/SourceControlBMPsApplicableToAllSite…1/3 You are here: 2019 SWMMWW > Volume IV - Source Control BMP Library > IV-1 Source Control BMPs Applicable to All Sites > S454 BMPs for Preventive Maintenance / Good Housekeeping S454 BMPs for Preventive Maintenance / Good Housekeeping Preventative maintenance and good housekeeping practices reduce the potential for stormwater to come into contact with pollutants and can reduce maintenance intervals for the drainage system and sewer system. Applicable BMPs: Prevent the discharge of unpermitted liquid or solid wastes, process wastewater, and sewage to ground or surface water, or to storm drains that discharge to surface water, or to the ground. Conduct all oily parts cleaning, steam cleaning, or pressure washing of equipment or containers inside a building, or on an impervious contained area, such as a concrete pad. Direct contaminated stormwater from such an area to a sanitary sewer where allowed by local sewer authority, or to other approved treatment. Promptly contain and clean up solid and liquid pollutant leaks and spills including oils, solvents, fuels, and dust from manufacturing operations on an exposed soil, vegetation, or paved area. If a contaminated surface must be pressure washed, collect the resulting washwater for proper disposal (usually involves plugging storm drains, or otherwise preventing discharge and pumping or vactoring up washwater, for discharge to sanitary sewer or for vactor truck transport to a waste water treatment plant for disposal). Do not hose down pollutants from any area to the ground, storm drains, conveyance ditches, or receiving water. Convey pollutants before discharge to a treatment system approved by the local jurisdiction. Sweep all appropriate surfaces with vacuum sweepers quarterly, or more frequently as needed, for the collection and disposal of dust and debris that could contaminate stormwater. Use mechanical sweepers, and manual sweeping as necessary to access areas that a vacuum sweeper can't reach to ensure that all surface contaminants are routinely removed. Do not pave over contaminated soil unless it has been determined that ground water has not been and will not be contaminated by the soil. Call Ecology for assistance. Construct impervious areas that are compatible with the materials handled. Portland cement concrete, asphalt, or equivalent material may be considered. Use drip pans to collect leaks and spills from industrial/commercial equipment such as cranes at ship/boat building and repair facilities, log stackers, industrial parts, trucks and other vehicles stored outside. At industrial and commercial facilities, drain oil and fuel filters before disposal. Discard empty oil and fuel filters, oily rags, and other oily solid waste into appropriately closed and properly labeled containers, and in compliance with the Uniform Fire Code or International Building Code. 12/21/2020 S454 BMPs for Preventive Maintenance / Good Housekeeping https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/SourceControlBMPsApplicableToAllSite…2/3 For the storage of liquids use containers, such as steel and plastic drums, that are rigid and durable, corrosion resistant to the weather and fluid content, non-absorbent, water tight, rodent-proof, and equipped with a close fitting cover. For the temporary storage of solid wastes contaminated with liquids or other potential polluted materials use dumpsters, garbage cans, drums, and comparable containers, which are durable, corrosion resistant, non- absorbent, non-leaking, and equipped with either a solid cover or screen cover to prevent littering. If covered with a screen, the container must be stored under a roof or other form of adequate cover. Where exposed to stormwater, use containers, piping, tubing, pumps, fittings, and valves that are appropriate for their intended use and for the contained liquid. Clean oils, debris, sludge, etc. from all stormwater facilities regularly, including catch basins, settling/detention basins, oil/water separators, boomed areas, and conveyance systems to prevent the contamination of stormwater. Refer to Ecology Requirements for Generators of Dangerous Wastes in I-2.15 Other Requirements for references to assist in handling potentially dangerous waste. Promptly repair or replace all substantially cracked or otherwise damaged paved secondary containment, high-intensity parking, and any other drainage areas, subjected to pollutant material leaks or spills. Promptly repair or replace all leaking connections, pipes, hoses, valves, etc., which can contaminate stormwater. Do not connect floor drains in potential pollutant source areas to storm drains, surface water, or to the ground. Recommended BMPs: Where feasible, store potential stormwater pollutant materials inside a building or under a cover and/or containment. Minimize use of toxic cleaning solvents, such as chlorinated solvents, and other toxic chemicals. Use environmentally safe raw materials, products, additives, etc. such as substitutes for zinc used in rubber production. Recycle waste materials such as solvents, coolants, oils, degreasers, and batteries to the maximum extent feasible. Contact Ecology's Hazardous Waste & Toxics Reduction Program at https://ecology.wa.gov/About- us/Get-to-know-us/Our-Programs/Hazardous-Waste-Toxics-Reduction for recommendations on recycling or disposal of vehicle waste liquids and other waste materials. Empty drip pans immediately after a spill or leak is collected in an uncovered area. Stencil warning signs at stormwater catch basins and drains, e.g., “Dump no waste – Drains to waterbody”. Use solid absorbents, e.g., clay and peat absorbents and rags for cleanup of liquid spills/leaks, where practicable. Promptly repair/replace/reseal damaged paved areas at industrial facilities. 12/21/2020 S454 BMPs for Preventive Maintenance / Good Housekeeping https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/SourceControlBMPsApplicableToAllSite…3/3 Recycle materials, such as oils, solvents, and wood waste, to the maximum extent practicable. Note: Evidence of stormwater contamination by oils and grease can include the presence of visible sheen, color, or turbidity in the runoff, or present or historical operational problems at the facility. Operators can use simple pH tests, for example with litmus or pH paper. These tests can screen for high or low pH levels (anything outside a 6.5-8.5 range) due to contamination in stormwater. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 S455 BMPs for Spill Prevention and Cleanup https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/SourceControlBMPsApplicableToAllSite…1/2 You are here: 2019 SWMMWW > Volume IV - Source Control BMP Library > IV-1 Source Control BMPs Applicable to All Sites > S455 BMPs for Spill Prevention and Cleanup S455 BMPs for Spill Prevention and Cleanup Description of Pollutant Sources: Spills and leaks can damage public infrastructure, interfere with sewage treatment, and cause a threat to human health or the environment. Spills are often preventable if appropriate chemical and waste handling techniques are practiced effectively and the spill response plan is immediately implemented. Additional spill control requirements may be required based on the specific activity occurring on site. Applicable BMPs: Spill Prevention Clearly label or mark all containers that contain potential pollutants. Store and transport liquid materials in appropriate containers with tight-fitting lids. Place drip pans underneath all containers, fittings, valves, and where materials are likely to spill or leak. Use tarpaulins, ground cloths, or drip pans in areas where materials are mixed, carried, and applied to capture any spilled materials. Train employees on the safe techniques for handling materials used on the site and to check for leaks and spills. Spill Plan Develop and implement a spill plan and update it annually or whenever there is a change in activities or staff responsible for spill cleanup. Post a written summary of the plan at areas with a high potential for spills, such as loading docks, product storage areas, waste storage areas, and near a phone. The spill plan may need to be posted at multiple locations. Describe the facility, including the owner's name, address, and telephone number; the nature of the facility activity; and the general types of chemicals used at the facility. Designate spill response employees to be on-site during business activities. Provide a current list of the names and telephone numbers (home and office) of designated spill response employees who are responsible for implementing the spill plan. Provide a site plan showing the locations of storage areas for chemicals, inlets/catch basins, spill kits and other relevant infrastructure or materials information. Describe the emergency cleanup and disposal procedures. Note the location of all spill kits in the spill plan. List the names and telephone numbers of public agencies to contact in the event of a spill. Spill Cleanup Kits 12/21/2020 S455 BMPs for Spill Prevention and Cleanup https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/SourceControlBMPsApplicableToAllSite…2/2 Store all cleanup kits near areas with a high potential for spills so that they are easily accessible in the event of a spill. The contents of the spill kit must be appropriate to the types and quantities of materials stored or otherwise used at the facility, and refilled when the materials are used. Spill kits must be located within 25 feet of all fueling/fuel transfer areas, including on-board mobile fuel trucks. Note: Ecology recommends that the kit(s) include salvage drums or containers, such as high density polyethylene, polypropylene or polyethylene sheet-lined steel; polyethylene or equivalent disposal bags; an emergency response guidebook; safety gloves/clothes/equipment; shovels or other soil removal equipment; and oil containment booms and absorbent pads; all stored in an impervious container. Spill Cleanup and Proper Disposal of Waste Stop, contain, and clean up all spills immediately upon discovery. Implement the spill plan immediately. Contact the designated spill response employees. Block off and seal nearby inlets/catch basins to prevent materials from entering the drainage system or combined sewer. Use the appropriate material to clean up the spill. Do not use emulsifiers or dispersants such as liquid detergents or degreasers unless disposed of proplerly. Emulsifiers and dispersants are not allowed to be used on surface water, or in a place where they may enter storm drains, surface waters, treatments systems, or sanitary sewers. Immediately notify Ecology and the local jurisdiction if a spill has reached or may reach a sanitary or storm sewer, ground water, or surface water. Notification must comply with state and federal spill reporting requirements. Do not wash absorbent material into interior floor drains or inlets/catch basins. Place used spill control materials in appropriate containers and dispose of according to regulations. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 S456 BMPs for Employee Training https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/SourceControlBMPsApplicableToAllSite…1/1 You are here: 2019 SWMMWW > Volume IV - Source Control BMP Library > IV-1 Source Control BMPs Applicable to All Sites > S456 BMPs for Employee Training S456 BMPs for Employee Training Train all employees that work in pollutant source areas about the following topics: Identifying Pollution Prevention Team Members. Identifying pollutant sources. Understanding pollutant control measures. Spill prevention and response. Emergency response procedures. Handling practices that are environmentally acceptable. Particularly those related to vehicle/equipment liquids such as fuels, and vehicle/equipment cleaning. Additional specialized training may be needed for staff who will be responsible for handling hazardous materials. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 S457 BMPS for Inspections https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/SourceControlBMPsApplicableToAllSite…1/1 You are here: 2019 SWMMWW > Volume IV - Source Control BMP Library > IV-1 Source Control BMPs Applicable to All Sites > S457 BMPS for Inspections S457 BMPS for Inspections Qualified personnel shall conduct inspections monthly. Make and maintain a record of each inspection on-site. The following requirements apply to inspections: Be conducted by someone familiar with the facility's site, operations, and BMPs. Verify the accuracy of the pollutant source descriptions in the SWPPP. Assess all BMPs that have been implemented for effectiveness and needed maintenance and locate areas where additional BMPs are needed. Reflect current conditions on the site. Include written observations of the presence of floating materials, suspended solids, oil and grease, discoloration, turbidity and odor in the stormwater discharges; in outside vehicle maintenance/repair; and liquid handling, and storage areas. In areas where acid or alkaline materials are handled or stored use a simple litmus or pH paper to identify those types of stormwater contaminants where needed. Eliminate or obtain a permit for unpermitted non-stormwater discharges to storm drains or receiving waters, such as process wastewater and vehicle/equipment washwater. Identify actions to address inspection deficiencies. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 S458 BMPs for Record Keeping https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/SourceControlBMPsApplicableToAllSite…1/2 You are here: 2019 SWMMWW > Volume IV - Source Control BMP Library > IV-1 Source Control BMPs Applicable to All Sites > S458 BMPs for Record Keeping S458 BMPs for Record Keeping See the applicable permit for specific record-keeping requirements and retention schedules for the following reports. At a minimum, retain the following reports for five years: Inspection reports which should include: Time and date of the inspection Locations inspected Statement on status of compliance with the permit Summary report of any remediation activities required Name, title, and signature of person conducting the inspection Reports on spills of oil or hazardous substances in greater than Reportable Quantities (Code of Federal Regulations Title 40 Parts 302.4 and 117). Report spills of the following: antifreeze, oil, gasoline, or diesel fuel, that cause: A violation of the State of Washington's Water Quality Standards. A film or sheen upon or discoloration of the waters of the State or adjoining shorelines. A sludge or emulsion to be deposited beneath the surface of the water or upon adjoining shorelines. To report a spill or to determine if a spill is a substance of a Reportable Quantity, call the Ecology regional office and ask for an oil spill operations or a dangerous waste specialist: Northwest Region (425)649-7000 Southwest Region (360)407-6300 Eastern Region (509)329-3400 Central Region (509) 575-2490 In addition, call the Washington Emergency Management Division at 1-800-258-5990 or 1-800-OILS-911 AND the National Response Center at 1-800-424-8802. Also, refer to Focus on Emergency Spill Response (Ecology, 2009). The following is additional recommended record keeping: 12/21/2020 S458 BMPs for Record Keeping https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeIV/SourceControlBMPsApplicableToAllSite…2/2 Maintain records of all related pollutant control and pollutant generating activities such as training, materials purchased, material use and disposal, maintenance performed, etc. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 ATTACHMENT G Flow Chart for Determining MR #5 Requirements Figure 1-3.3: Flow Chart for Determining MR #5 Requirements Does the entire project qualify as Flow Control exempt (per MR #7)? Yes I I No Did the project developer choose to meet Does the project trigger the LID Performance Standard? only MRs #1 - #5? (Per the Project Thresholds in N� Applicability of the Minimum Requirements veS Section). REQUIRFD: For each surface, consider the BMPs Ye$ in the order listed in List 43 for that type of surffarre. Use the brat BMP that is Did the project considered feasible. developer choose meet the L0 NOT REQUIRED' Performance Achievement of the LID Standard? Performance Standard. No REQUIRED: For each surface, consider the BMPs in the order listed in List 91 for that type of surface. Use the first BMP that is considered feasible. NOT REQUIRED: Achievement of the LID Perronnance Standard. REQUIRED: Meet ase LID Performance Standard through the use of any Flow Control BMP(s) in this manual. REQUIRES): Apply BMP T5,13 Post Construction Soil Quality and Depth. NOT REQUIRED: Applying the BMPs In Lists #1, #x, or #3. r►� DEPARTMENT OF ECOLOGY State of Washington Yes No (the project triggers MRS 41 - #9} Yes REQUIRED. For each surface, consider the BMPs in the order listed in List #2 for that type of surface. Use the first BMP that Is considered feasible. NOT REQUIRED: Achievement of the LID Performance Standard. Is the project outside the UGA on a parcel that is 5 acres or larcia No IF Yes Did the project developer choose to meet the LI D Performance Standard? /No REQUIRED: Meet the LID Performance Standard through the use of any Flow Control BMP(s) in this manual. REQUIRED: Apply BMP T5.13 Post -Construction Soil Quality and Depth. NOT REQUIRED: Applying the BMPs in Lists #1, 92, or #3. Flow Chart for Determining MR #5 Requirements Revised March 2019 Please see hMp.,IAvww.ecy.wa.gov/copyright h#ml for copyright notice including permissions, limitation of liability, and disclaimer. 2019 Stormwater Management Manual for Western Washington Volume 1- Chapter 3 - Page 118 ATTACHMENT H WWHM 2012 Results WWHM2012 PROJECT REPORT One North Basin_12-22-20 12/22/2020 3:53:31 PM Page 2 General Model Information Project Name: One North Basin_12-22-20 Site Name: Modern Resources LLC Site Address: 1102 Rhoton Rd SE City:Yelm Report Date: 12/22/2020 Gage:Lake Lawrence Data Start: 1955/10/01 Data End: 2008/09/30 Timestep: 15 Minute Precip Scale: 0.857 Version Date: 2019/09/13 Version: 4.2.17 POC Thresholds Low Flow Threshold for POC1: 50 Percent of the 2 Year High Flow Threshold for POC1: 50 Year One North Basin_12-22-20 12/22/2020 3:53:31 PM Page 3 Landuse Basin Data Predeveloped Land Use One North Basin_12-22-20 12/22/2020 3:53:31 PM Page 4 Mitigated Land Use Bioretention Contributing Basin Bypass:No GroundWater:No Pervious Land Use acre A B, Forest, Mod 0.201 A B, Lawn, Flat 0.0395 Pervious Total 0.2405 Impervious Land Use acre PARKING FLAT 0.917 Impervious Total 0.917 Basin Total 1.1575 Element Flows To: Surface Interflow Groundwater Surface Bioretention Surface Bioretention One North Basin_12-22-20 12/22/2020 3:53:31 PM Page 5 Infilitration Gallery Contributing Basin Bypass:No GroundWater:No Pervious Land Use acre A B, Lawn, Flat 0.053 A B, Forest, Mod 0.306 Pervious Total 0.359 Impervious Land Use acre ROOF TOPS FLAT 0.5675 Impervious Total 0.5675 Basin Total 0.9265 Element Flows To: Surface Interflow Groundwater Total Required Gravel Infiltration TrenchTotal Required Gravel Infiltration Trench One North Basin_12-22-20 12/22/2020 3:53:31 PM Page 6 Routing Elements Predeveloped Routing One North Basin_12-22-20 12/22/2020 3:53:31 PM Page 7 Mitigated Routing 153 LF Bioretention Bottom Length: 102.74 ft. Bottom Width: 9.34 ft. Material thickness of first layer: 0.25 Material type for first layer: ASTM 100 Material thickness of second layer: 1.5 Material type for second layer: SMMWW 12 in/hr Material thickness of third layer: 3 Material type for third layer: GRAVEL Infiltration On Infiltration rate:1 Infiltration safety factor:1 Total Volume Infiltrated (ac-ft.):168.586 Total Volume Through Riser (ac-ft.): 1.946 Total Volume Through Facility (ac-ft.): 170.532 Percent Infiltrated:98.86 Total Precip Applied to Facility:15.115 Total Evap From Facility:5.606 Underdrain not used Discharge Structure Riser Height:1.5 ft. Riser Diameter:12 in. Element Flows To: Outlet 1 Outlet 2 Total Required Gravel Infiltration Trench Bioretention Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.1140 0.0000 0.0000 0.0000 0.0742 0.1139 0.0008 0.0000 0.0000 0.1484 0.1122 0.0017 0.0000 0.0000 0.2225 0.1105 0.0027 0.0000 0.0000 0.2967 0.1088 0.0036 0.0000 0.0004 0.3709 0.1071 0.0045 0.0000 0.0004 0.4451 0.1054 0.0054 0.0000 0.0008 0.5192 0.1037 0.0065 0.0000 0.0015 0.5934 0.1021 0.0075 0.0000 0.0020 0.6676 0.1004 0.0086 0.0000 0.0024 0.7418 0.0988 0.0097 0.0000 0.0036 0.8159 0.0971 0.0109 0.0000 0.0049 0.8901 0.0955 0.0121 0.0000 0.0052 0.9643 0.0939 0.0134 0.0000 0.0071 1.0385 0.0922 0.0147 0.0000 0.0094 1.1126 0.0906 0.0160 0.0000 0.0097 1.1868 0.0890 0.0174 0.0000 0.0121 1.2610 0.0875 0.0188 0.0000 0.0152 1.3352 0.0859 0.0203 0.0000 0.0164 1.4093 0.0843 0.0218 0.0000 0.0188 1.4835 0.0828 0.0234 0.0000 0.0222 1.5577 0.0812 0.0250 0.0000 0.0222 1.6319 0.0797 0.0266 0.0000 0.0222 1.7060 0.0781 0.0283 0.0000 0.0222 1.7802 0.0766 0.0299 0.0000 0.0222 1.8544 0.0751 0.0315 0.0000 0.0222 One North Basin_12-22-20 12/22/2020 3:53:31 PM Page 8 1.9286 0.0736 0.0332 0.0000 0.0222 2.0027 0.0721 0.0349 0.0000 0.0222 2.0769 0.0706 0.0367 0.0000 0.0222 2.1511 0.0691 0.0385 0.0000 0.0222 2.2253 0.0677 0.0403 0.0000 0.0222 2.2995 0.0662 0.0422 0.0000 0.0222 2.3736 0.0648 0.0441 0.0000 0.0222 2.4478 0.0633 0.0461 0.0000 0.0222 2.5220 0.0619 0.0481 0.0000 0.0222 2.5962 0.0605 0.0502 0.0000 0.0222 2.6703 0.0591 0.0523 0.0000 0.0222 2.7445 0.0576 0.0544 0.0000 0.0222 2.8187 0.0563 0.0566 0.0000 0.0222 2.8929 0.0549 0.0589 0.0000 0.0222 2.9670 0.0535 0.0612 0.0000 0.0222 3.0412 0.0521 0.0635 0.0000 0.0222 3.1154 0.0508 0.0659 0.0000 0.0222 3.1896 0.0494 0.0683 0.0000 0.0222 3.2637 0.0481 0.0708 0.0000 0.0222 3.3379 0.0467 0.0733 0.0000 0.0222 3.4121 0.0454 0.0759 0.0000 0.0222 3.4863 0.0441 0.0785 0.0000 0.0222 3.5604 0.0428 0.0812 0.0000 0.0222 3.6346 0.0415 0.0839 0.0000 0.0222 3.7088 0.0402 0.0866 0.0000 0.0222 3.7830 0.0389 0.0895 0.0000 0.0222 3.8571 0.0377 0.0923 0.0000 0.0222 3.9313 0.0364 0.0952 0.0000 0.0222 4.0055 0.0352 0.0982 0.0000 0.0222 4.0797 0.0339 0.1012 0.0000 0.0222 4.1538 0.0327 0.1043 0.0000 0.0222 4.2280 0.0315 0.1074 0.0000 0.0222 4.3022 0.0303 0.1106 0.0000 0.0222 4.3764 0.0291 0.1138 0.0000 0.0222 4.4505 0.0279 0.1171 0.0000 0.0222 4.5247 0.0267 0.1204 0.0000 0.0222 4.5989 0.0255 0.1238 0.0000 0.0222 4.6731 0.0243 0.1272 0.0000 0.0222 4.7473 0.0232 0.1307 0.0000 0.0222 4.7500 0.0220 0.1308 0.0000 0.0222 Bioretention Hydraulic Table Stage(feet)Area(ac.)Volume(ac-ft.)Discharge(cfs)To Amended(cfs)Infilt(cfs) 4.7500 0.1140 0.1308 0.0000 0.0810 0.0000 4.8242 0.1157 0.1393 0.0000 0.0810 0.0000 4.8984 0.1175 0.1480 0.0000 0.0843 0.0000 4.9725 0.1192 0.1567 0.0000 0.0876 0.0000 5.0467 0.1210 0.1656 0.0000 0.0909 0.0000 5.1209 0.1227 0.1747 0.0000 0.0942 0.0000 5.1951 0.1245 0.1839 0.0000 0.0975 0.0000 5.2692 0.1263 0.1932 0.0000 0.1008 0.0000 5.3434 0.1281 0.2026 0.0000 0.1041 0.0000 5.4176 0.1299 0.2122 0.0000 0.1074 0.0000 5.4918 0.1317 0.2219 0.0000 0.1107 0.0000 5.5659 0.1335 0.2317 0.0000 0.1140 0.0000 5.6401 0.1354 0.2417 0.0000 0.1173 0.0000 5.7143 0.1372 0.2518 0.0000 0.1205 0.0000 5.7885 0.1391 0.2620 0.0000 0.1238 0.0000 One North Basin_12-22-20 12/22/2020 3:53:31 PM Page 9 5.8626 0.1409 0.2724 0.0000 0.1271 0.0000 5.9368 0.1428 0.2829 0.0000 0.1304 0.0000 6.0110 0.1447 0.2936 0.0000 0.1337 0.0000 6.0852 0.1466 0.3044 0.0000 0.1370 0.0000 6.1593 0.1485 0.3154 0.0000 0.1403 0.0000 6.2335 0.1504 0.3264 0.0000 0.1436 0.0000 6.3077 0.1523 0.3377 0.1468 0.1469 0.0000 6.3819 0.1542 0.3490 0.5015 0.1502 0.0000 6.4560 0.1561 0.3605 0.9453 0.1535 0.0000 6.5302 0.1581 0.3722 1.3977 0.1568 0.0000 6.6044 0.1600 0.3840 1.7818 0.1601 0.0000 6.6786 0.1620 0.3959 2.0472 0.1634 0.0000 6.7500 0.1639 0.4076 2.2332 0.1665 0.0000 One North Basin_12-22-20 12/22/2020 3:53:31 PM Page 10 Surface Bioretention Element Flows To: Outlet 1 Outlet 2 Total Required Gravel Infiltration Trench153 LF Bioretention One North Basin_12-22-20 12/22/2020 3:53:31 PM Page 11 Total Required Gravel Infiltration Trench Bottom Length:500.00 ft. Bottom Width:34.00 ft. Trench bottom slope 1:0 To 1 Trench Left side slope 0:0 To 1 Trench right side slope 2:0 To 1 Material thickness of first layer:3 Pour Space of material for first layer: 0.3 Material thickness of second layer:0 Pour Space of material for second layer: 0 Material thickness of third layer:0 Pour Space of material for third layer: 0 Infiltration On Infiltration rate:1 Infiltration safety factor:1 Total Volume Infiltrated (ac-ft.):177.307 Total Volume Through Riser (ac-ft.): 0 Total Volume Through Facility (ac-ft.): 177.307 Percent Infiltrated:100 Total Precip Applied to Facility:75.677 Total Evap From Facility:0 Discharge Structure Riser Height:3 ft. Riser Diameter:12 in. Element Flows To: Outlet 1 Outlet 2 Gravel Trench Bed Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.390 0.000 0.000 0.000 0.0444 0.390 0.005 0.000 0.393 0.0889 0.390 0.010 0.000 0.393 0.1333 0.390 0.015 0.000 0.393 0.1778 0.390 0.020 0.000 0.393 0.2222 0.390 0.026 0.000 0.393 0.2667 0.390 0.031 0.000 0.393 0.3111 0.390 0.036 0.000 0.393 0.3556 0.390 0.041 0.000 0.393 0.4000 0.390 0.046 0.000 0.393 0.4444 0.390 0.052 0.000 0.393 0.4889 0.390 0.057 0.000 0.393 0.5333 0.390 0.062 0.000 0.393 0.5778 0.390 0.067 0.000 0.393 0.6222 0.390 0.072 0.000 0.393 0.6667 0.390 0.078 0.000 0.393 0.7111 0.390 0.083 0.000 0.393 0.7556 0.390 0.088 0.000 0.393 0.8000 0.390 0.093 0.000 0.393 0.8444 0.390 0.098 0.000 0.393 0.8889 0.390 0.104 0.000 0.393 0.9333 0.390 0.109 0.000 0.393 0.9778 0.390 0.114 0.000 0.393 1.0222 0.390 0.119 0.000 0.393 1.0667 0.390 0.124 0.000 0.393 1.1111 0.390 0.130 0.000 0.393 One North Basin_12-22-20 12/22/2020 3:53:31 PM Page 12 1.1556 0.390 0.135 0.000 0.393 1.2000 0.390 0.140 0.000 0.393 1.2444 0.390 0.145 0.000 0.393 1.2889 0.390 0.150 0.000 0.393 1.3333 0.390 0.156 0.000 0.393 1.3778 0.390 0.161 0.000 0.393 1.4222 0.390 0.166 0.000 0.393 1.4667 0.390 0.171 0.000 0.393 1.5111 0.390 0.176 0.000 0.393 1.5556 0.390 0.182 0.000 0.393 1.6000 0.390 0.187 0.000 0.393 1.6444 0.390 0.192 0.000 0.393 1.6889 0.390 0.197 0.000 0.393 1.7333 0.390 0.202 0.000 0.393 1.7778 0.390 0.208 0.000 0.393 1.8222 0.390 0.213 0.000 0.393 1.8667 0.390 0.218 0.000 0.393 1.9111 0.390 0.223 0.000 0.393 1.9556 0.390 0.229 0.000 0.393 2.0000 0.390 0.234 0.000 0.393 2.0444 0.390 0.239 0.000 0.393 2.0889 0.390 0.244 0.000 0.393 2.1333 0.390 0.249 0.000 0.393 2.1778 0.390 0.255 0.000 0.393 2.2222 0.390 0.260 0.000 0.393 2.2667 0.390 0.265 0.000 0.393 2.3111 0.390 0.270 0.000 0.393 2.3556 0.390 0.275 0.000 0.393 2.4000 0.390 0.281 0.000 0.393 2.4444 0.390 0.286 0.000 0.393 2.4889 0.390 0.291 0.000 0.393 2.5333 0.390 0.296 0.000 0.393 2.5778 0.390 0.301 0.000 0.393 2.6222 0.390 0.307 0.000 0.393 2.6667 0.390 0.312 0.000 0.393 2.7111 0.390 0.317 0.000 0.393 2.7556 0.390 0.322 0.000 0.393 2.8000 0.390 0.327 0.000 0.393 2.8444 0.390 0.333 0.000 0.393 2.8889 0.390 0.338 0.000 0.393 2.9333 0.390 0.343 0.000 0.393 2.9778 0.390 0.348 0.000 0.393 3.0222 0.390 0.366 0.035 0.393 3.0667 0.390 0.383 0.182 0.393 3.1111 0.390 0.400 0.389 0.393 3.1556 0.390 0.418 0.637 0.393 3.2000 0.390 0.435 0.907 0.393 3.2444 0.390 0.452 1.183 0.393 3.2889 0.390 0.470 1.447 0.393 3.3333 0.390 0.487 1.683 0.393 3.3778 0.390 0.504 1.879 0.393 3.4222 0.390 0.522 2.029 0.393 3.4667 0.390 0.539 2.138 0.393 3.5111 0.390 0.556 2.251 0.393 3.5556 0.390 0.574 2.347 0.393 3.6000 0.390 0.591 2.439 0.393 3.6444 0.390 0.608 2.528 0.393 3.6889 0.390 0.626 2.614 0.393 One North Basin_12-22-20 12/22/2020 3:53:31 PM Page 13 3.7333 0.390 0.643 2.697 0.393 3.7778 0.390 0.660 2.777 0.393 3.8222 0.390 0.678 2.856 0.393 3.8667 0.390 0.695 2.932 0.393 3.9111 0.390 0.712 3.006 0.393 3.9556 0.390 0.730 3.078 0.393 4.0000 0.390 0.747 3.149 0.393 One North Basin_12-22-20 12/22/2020 3:53:31 PM Page 14 Analysis Results POC 1 POC #1 was not reported because POC must exist in both scenarios and both scenarios must have been run. One North Basin_12-22-20 12/22/2020 3:53:31 PM Page 15 POC 2 POC #2 was not reported because POC must exist in both scenarios and both scenarios must have been run. One North Basin_12-22-20 12/22/2020 3:53:31 PM Page 16 Model Default Modifications Total of 0 changes have been made. PERLND Changes No PERLND changes have been made. IMPLND Changes No IMPLND changes have been made. One North Basin_12-22-20 12/22/2020 3:53:31 PM Page 17 Appendix Predeveloped Schematic One North Basin_12-22-20 12/22/2020 3:53:33 PM Page 18 Mitigated Schematic One North Basin_12-22-20 12/22/2020 3:53:35 PM Page 19 Predeveloped UCI File One North Basin_12-22-20 12/22/2020 3:53:35 PM Page 20 Mitigated UCI File RUN GLOBAL WWHM4 model simulation START 1955 10 01 END 2008 09 30 RUN INTERP OUTPUT LEVEL 3 0 RESUME 0 RUN 1 UNIT SYSTEM 1 END GLOBAL FILES <File> <Un#> <-----------File Name------------------------------>*** <-ID-> *** WDM 26 One North Basin_12-22-20.wdm MESSU 25 MitOne North Basin_12-22-20.MES 27 MitOne North Basin_12-22-20.L61 28 MitOne North Basin_12-22-20.L62 30 POCOne North Basin_12-22-201.dat END FILES OPN SEQUENCE INGRP INDELT 00:15 PERLND 2 PERLND 7 IMPLND 11 IMPLND 4 GENER 2 RCHRES 1 RCHRES 2 RCHRES 3 COPY 1 COPY 501 DISPLY 1 END INGRP END OPN SEQUENCE DISPLY DISPLY-INFO1 # - #<----------Title----------->***TRAN PIVL DIG1 FIL1 PYR DIG2 FIL2 YRND 1 Total Required Gravel Inf MAX 1 2 30 9 END DISPLY-INFO1 END DISPLY COPY TIMESERIES # - # NPT NMN *** 1 1 1 501 1 1 END TIMESERIES END COPY GENER OPCODE # # OPCD *** 2 24 END OPCODE PARM # # K *** 2 0. END PARM END GENER PERLND GEN-INFO <PLS ><-------Name------->NBLKS Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** 2 A/B, Forest, Mod 1 1 1 1 27 0 7 A/B, Lawn, Flat 1 1 1 1 27 0 END GEN-INFO *** Section PWATER*** ACTIVITY One North Basin_12-22-20 12/22/2020 3:53:35 PM Page 21 <PLS > ************* Active Sections ***************************** # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC *** 2 0 0 1 0 0 0 0 0 0 0 0 0 7 0 0 1 0 0 0 0 0 0 0 0 0 END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ***************************** PIVL PYR # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ********* 2 0 0 4 0 0 0 0 0 0 0 0 0 1 9 7 0 0 4 0 0 0 0 0 0 0 0 0 1 9 END PRINT-INFO PWAT-PARM1 <PLS > PWATER variable monthly parameter value flags *** # - # CSNO RTOP UZFG VCS VUZ VNN VIFW VIRC VLE INFC HWT *** 2 0 0 0 0 0 0 0 0 0 0 0 7 0 0 0 0 0 0 0 0 0 0 0 END PWAT-PARM1 PWAT-PARM2 <PLS > PWATER input info: Part 2 *** # - # ***FOREST LZSN INFILT LSUR SLSUR KVARY AGWRC 2 0 5 2 400 0.1 0.3 0.996 7 0 5 0.8 400 0.05 0.3 0.996 END PWAT-PARM2 PWAT-PARM3 <PLS > PWATER input info: Part 3 *** # - # ***PETMAX PETMIN INFEXP INFILD DEEPFR BASETP AGWETP 2 0 0 2 2 0 0 0 7 0 0 2 2 0 0 0 END PWAT-PARM3 PWAT-PARM4 <PLS > PWATER input info: Part 4 *** # - # CEPSC UZSN NSUR INTFW IRC LZETP *** 2 0.2 0.5 0.35 0 0.7 0.7 7 0.1 0.5 0.25 0 0.7 0.25 END PWAT-PARM4 PWAT-STATE1 <PLS > *** Initial conditions at start of simulation ran from 1990 to end of 1992 (pat 1-11-95) RUN 21 *** # - # *** CEPS SURS UZS IFWS LZS AGWS GWVS 2 0 0 0 0 3 1 0 7 0 0 0 0 3 1 0 END PWAT-STATE1 END PERLND IMPLND GEN-INFO <PLS ><-------Name-------> Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** 11 PARKING/FLAT 1 1 1 27 0 4 ROOF TOPS/FLAT 1 1 1 27 0 END GEN-INFO *** Section IWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW IWAT SLD IWG IQAL *** 11 0 0 1 0 0 0 4 0 0 1 0 0 0 END ACTIVITY PRINT-INFO <ILS > ******** Print-flags ******** PIVL PYR # - # ATMP SNOW IWAT SLD IWG IQAL ********* One North Basin_12-22-20 12/22/2020 3:53:35 PM Page 22 11 0 0 4 0 0 0 1 9 4 0 0 4 0 0 0 1 9 END PRINT-INFO IWAT-PARM1 <PLS > IWATER variable monthly parameter value flags *** # - # CSNO RTOP VRS VNN RTLI *** 11 0 0 0 0 0 4 0 0 0 0 0 END IWAT-PARM1 IWAT-PARM2 <PLS > IWATER input info: Part 2 *** # - # *** LSUR SLSUR NSUR RETSC 11 400 0.01 0.1 0.1 4 400 0.01 0.1 0.1 END IWAT-PARM2 IWAT-PARM3 <PLS > IWATER input info: Part 3 *** # - # ***PETMAX PETMIN 11 0 0 4 0 0 END IWAT-PARM3 IWAT-STATE1 <PLS > *** Initial conditions at start of simulation # - # *** RETS SURS 11 0 0 4 0 0 END IWAT-STATE1 END IMPLND SCHEMATIC <-Source-> <--Area--> <-Target-> MBLK *** <Name> # <-factor-> <Name> # Tbl# *** Bioretention Contributing Basin*** PERLND 2 0.201 RCHRES 1 2 PERLND 2 0.201 RCHRES 1 3 PERLND 7 0.0395 RCHRES 1 2 PERLND 7 0.0395 RCHRES 1 3 IMPLND 11 0.917 RCHRES 1 5 Infilitration Gallery Contributing Basin*** PERLND 7 0.053 RCHRES 3 2 PERLND 7 0.053 RCHRES 3 3 PERLND 2 0.306 RCHRES 3 2 PERLND 2 0.306 RCHRES 3 3 IMPLND 4 0.5675 RCHRES 3 5 ******Routing****** RCHRES 2 1 RCHRES 3 7 RCHRES 2 COPY 1 17 RCHRES 1 1 RCHRES 3 7 RCHRES 1 COPY 1 17 RCHRES 1 1 RCHRES 2 8 PERLND 7 0.053 COPY 1 12 PERLND 2 0.306 COPY 1 12 IMPLND 4 0.5675 COPY 1 15 PERLND 7 0.053 COPY 1 13 PERLND 2 0.306 COPY 1 13 RCHRES 3 1 COPY 501 17 END SCHEMATIC NETWORK <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** COPY 501 OUTPUT MEAN 1 1 48.4 DISPLY 1 INPUT TIMSER 1 GENER 2 OUTPUT TIMSER .0011111 RCHRES 1 EXTNL OUTDGT 1 One North Basin_12-22-20 12/22/2020 3:53:35 PM Page 23 <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** END NETWORK RCHRES GEN-INFO RCHRES Name Nexits Unit Systems Printer *** # - #<------------------><---> User T-series Engl Metr LKFG *** in out *** 1 Surface Bioreten-011 2 1 1 1 28 0 1 2 153 LF Bioretent-010 2 1 1 1 28 0 1 3 Total Required G-017 2 1 1 1 28 0 1 END GEN-INFO *** Section RCHRES*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # HYFG ADFG CNFG HTFG SDFG GQFG OXFG NUFG PKFG PHFG *** 1 1 0 0 0 0 0 0 0 0 0 2 1 0 0 0 0 0 0 0 0 0 3 1 0 0 0 0 0 0 0 0 0 END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ******************* PIVL PYR # - # HYDR ADCA CONS HEAT SED GQL OXRX NUTR PLNK PHCB PIVL PYR ********* 1 4 0 0 0 0 0 0 0 0 0 1 9 2 4 0 0 0 0 0 0 0 0 0 1 9 3 4 0 0 0 0 0 0 0 0 0 1 9 END PRINT-INFO HYDR-PARM1 RCHRES Flags for each HYDR Section *** # - # VC A1 A2 A3 ODFVFG for each *** ODGTFG for each FUNCT for each FG FG FG FG possible exit *** possible exit possible exit * * * * * * * * * * * * * * *** 1 0 1 0 0 4 5 0 0 0 0 1 0 0 0 2 1 2 2 2 2 0 1 0 0 4 5 0 0 0 0 0 0 0 0 2 2 2 2 2 3 0 1 0 0 4 5 0 0 0 0 0 0 0 0 2 2 2 2 2 END HYDR-PARM1 HYDR-PARM2 # - # FTABNO LEN DELTH STCOR KS DB50 *** <------><--------><--------><--------><--------><--------><--------> *** 1 1 0.01 0.0 0.0 0.0 0.0 2 2 0.02 0.0 0.0 0.0 0.0 3 3 0.09 0.0 0.0 0.5 0.0 END HYDR-PARM2 HYDR-INIT RCHRES Initial conditions for each HYDR section *** # - # *** VOL Initial value of COLIND Initial value of OUTDGT *** ac-ft for each possible exit for each possible exit <------><--------> <---><---><---><---><---> *** <---><---><---><---><---> 1 0 4.0 5.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 2 0 4.0 5.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 3 0 4.0 5.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 END HYDR-INIT END RCHRES SPEC-ACTIONS *** User-Defined Variable Quantity Lines *** addr *** <------> *** kwd varnam optyp opn vari s1 s2 s3 tp multiply lc ls ac as agfn *** <****> <----> <----> <-> <----><-><-><-><-><--------> <><-> <><-> <--> *** UVQUAN vol2 RCHRES 2 VOL 4 UVQUAN v2m2 GLOBAL WORKSP 1 3 UVQUAN vpo2 GLOBAL WORKSP 2 3 One North Basin_12-22-20 12/22/2020 3:53:35 PM Page 24 UVQUAN v2d2 GENER 2 K 1 3 *** User-Defined Target Variable Names *** addr or addr or *** <------> <------> *** kwd varnam ct vari s1 s2 s3 frac oper vari s1 s2 s3 frac oper <****> <----><-> <----><-><-><-> <---> <--> <----><-><-><-> <---> <--> UVNAME v2m2 1 WORKSP 1 1.0 QUAN UVNAME vpo2 1 WORKSP 2 1.0 QUAN UVNAME v2d2 1 K 1 1.0 QUAN *** opt foplop dcdts yr mo dy hr mn d t vnam s1 s2 s3 ac quantity tc ts rp <****><-><--><><-><--> <> <> <> <><><> <----><-><-><-><-><--------> <> <-><-> GENER 2 v2m2 = 5717.16 *** Compute remaining available pore space GENER 2 vpo2 = v2m2 GENER 2 vpo2 -= vol2 *** Check to see if VPORA goes negative; if so set VPORA = 0.0 IF (vpo2 < 0.0) THEN GENER 2 vpo2 = 0.0 END IF *** Infiltration volume GENER 2 v2d2 = vpo2 END SPEC-ACTIONS FTABLES FTABLE 2 66 5 Depth Area Volume Outflow1 Outflow2 Velocity Travel Time*** (ft) (acres) (acre-ft) (cfs) (cfs) (ft/sec) (Minutes)*** 0.000000 0.113997 0.000000 0.000000 0.000000 0.074176 0.113933 0.000846 0.000000 0.000000 0.148352 0.112211 0.001736 0.000000 0.000000 0.222527 0.110497 0.002669 0.000000 0.000000 0.296703 0.108793 0.003554 0.000000 0.000373 0.370879 0.107098 0.004479 0.000000 0.000441 0.445055 0.105411 0.005445 0.000000 0.000808 0.519231 0.103734 0.006451 0.000000 0.001473 0.593407 0.102066 0.007498 0.000000 0.001958 0.667582 0.100407 0.008586 0.000000 0.002406 0.741758 0.098758 0.009716 0.000000 0.003639 0.815934 0.097117 0.010888 0.000000 0.004934 0.890110 0.095485 0.012102 0.000000 0.005201 0.964286 0.093863 0.013359 0.000000 0.007117 1.038462 0.092249 0.014658 0.000000 0.009412 1.112637 0.090645 0.016001 0.000000 0.009673 1.186813 0.089050 0.017387 0.000000 0.012110 1.260989 0.087463 0.018817 0.000000 0.015232 1.335165 0.085886 0.020291 0.000000 0.016433 1.409341 0.084318 0.021809 0.000000 0.018797 1.483516 0.082759 0.023373 0.000000 0.022206 1.557692 0.081210 0.024981 0.000000 0.022206 1.631868 0.079669 0.026634 0.000000 0.022206 1.706044 0.078137 0.028333 0.000000 0.022206 1.780220 0.076615 0.029917 0.000000 0.022206 1.854396 0.075101 0.031542 0.000000 0.022206 1.928571 0.073597 0.033210 0.000000 0.022206 2.002747 0.072102 0.034921 0.000000 0.022206 2.076923 0.070616 0.036674 0.000000 0.022206 2.151099 0.069139 0.038470 0.000000 0.022206 2.225275 0.067671 0.040310 0.000000 0.022206 2.299451 0.066212 0.042193 0.000000 0.022206 2.373626 0.064762 0.044120 0.000000 0.022206 2.447802 0.063322 0.046091 0.000000 0.022206 2.521978 0.061890 0.048107 0.000000 0.022206 2.596154 0.060467 0.050168 0.000000 0.022206 2.670330 0.059054 0.052274 0.000000 0.022206 2.744505 0.057650 0.054425 0.000000 0.022206 2.818681 0.056255 0.056621 0.000000 0.022206 2.892857 0.054869 0.058864 0.000000 0.022206 2.967033 0.053492 0.061153 0.000000 0.022206 3.041209 0.052124 0.063488 0.000000 0.022206 3.115385 0.050765 0.065870 0.000000 0.022206 One North Basin_12-22-20 12/22/2020 3:53:35 PM Page 25 3.189560 0.049415 0.068298 0.000000 0.022206 3.263736 0.048074 0.070775 0.000000 0.022206 3.337912 0.046743 0.073298 0.000000 0.022206 3.412088 0.045420 0.075870 0.000000 0.022206 3.486264 0.044107 0.078490 0.000000 0.022206 3.560440 0.042803 0.081158 0.000000 0.022206 3.634615 0.041508 0.083874 0.000000 0.022206 3.708791 0.040222 0.086640 0.000000 0.022206 3.782967 0.038945 0.089455 0.000000 0.022206 3.857143 0.037677 0.092320 0.000000 0.022206 3.931319 0.036418 0.095234 0.000000 0.022206 4.005495 0.035168 0.098199 0.000000 0.022206 4.079670 0.033928 0.101213 0.000000 0.022206 4.153846 0.032696 0.104279 0.000000 0.022206 4.228022 0.031474 0.107395 0.000000 0.022206 4.302198 0.030261 0.110563 0.000000 0.022206 4.376374 0.029056 0.113782 0.000000 0.022206 4.450549 0.027861 0.117053 0.000000 0.022206 4.524725 0.026675 0.120376 0.000000 0.022206 4.598901 0.025498 0.123751 0.000000 0.022206 4.673077 0.024330 0.127179 0.000000 0.022206 4.747253 0.023172 0.130659 0.000000 0.022206 4.750000 0.022022 0.131248 0.000000 0.022206 END FTABLE 2 FTABLE 1 28 5 Depth Area Volume Outflow1 Outflow2 Velocity Travel Time*** (ft) (acres) (acre-ft) (cfs) (cfs) (ft/sec) (Minutes)*** 0.000000 0.022022 0.000000 0.000000 0.000000 0.074176 0.115729 0.008520 0.000000 0.081014 0.148352 0.117471 0.017169 0.000000 0.084308 0.222527 0.119221 0.025947 0.000000 0.087603 0.296703 0.120980 0.034856 0.000000 0.090897 0.370879 0.122748 0.043895 0.000000 0.094191 0.445055 0.124526 0.053066 0.000000 0.097485 0.519231 0.126313 0.062369 0.000000 0.100779 0.593407 0.128108 0.071805 0.000000 0.104074 0.667582 0.129913 0.081375 0.000000 0.107368 0.741758 0.131727 0.091078 0.000000 0.110662 0.815934 0.133550 0.100917 0.000000 0.113956 0.890110 0.135382 0.110891 0.000000 0.117251 0.964286 0.137223 0.121001 0.000000 0.120545 1.038462 0.139073 0.131249 0.000000 0.123839 1.112637 0.140933 0.141633 0.000000 0.127133 1.186813 0.142801 0.152157 0.000000 0.130428 1.260989 0.144679 0.162819 0.000000 0.133722 1.335165 0.146565 0.173620 0.000000 0.137016 1.409341 0.148461 0.184562 0.000000 0.140310 1.483516 0.150366 0.195645 0.000000 0.143605 1.557692 0.152280 0.206869 0.146791 0.146899 1.631868 0.154203 0.218236 0.501498 0.150193 1.706044 0.156135 0.229746 0.945261 0.153487 1.780220 0.158076 0.241399 1.397744 0.156782 1.854396 0.160026 0.253197 1.781797 0.160076 1.928571 0.161985 0.265140 2.047214 0.163370 2.000000 0.163881 0.276778 2.233235 0.166542 END FTABLE 1 FTABLE 3 92 5 Depth Area Volume Outflow1 Outflow2 Velocity Travel Time*** (ft) (acres) (acre-ft) (cfs) (cfs) (ft/sec) (Minutes)*** 0.000000 0.390266 0.000000 0.000000 0.000000 0.044444 0.390266 0.005204 0.000000 0.393519 0.088889 0.390266 0.010407 0.000000 0.393519 0.133333 0.390266 0.015611 0.000000 0.393519 0.177778 0.390266 0.020814 0.000000 0.393519 0.222222 0.390266 0.026018 0.000000 0.393519 0.266667 0.390266 0.031221 0.000000 0.393519 0.311111 0.390266 0.036425 0.000000 0.393519 0.355556 0.390266 0.041628 0.000000 0.393519 One North Basin_12-22-20 12/22/2020 3:53:35 PM Page 26 0.400000 0.390266 0.046832 0.000000 0.393519 0.444444 0.390266 0.052036 0.000000 0.393519 0.488889 0.390266 0.057239 0.000000 0.393519 0.533333 0.390266 0.062443 0.000000 0.393519 0.577778 0.390266 0.067646 0.000000 0.393519 0.622222 0.390266 0.072850 0.000000 0.393519 0.666667 0.390266 0.078053 0.000000 0.393519 0.711111 0.390266 0.083257 0.000000 0.393519 0.755556 0.390266 0.088460 0.000000 0.393519 0.800000 0.390266 0.093664 0.000000 0.393519 0.844444 0.390266 0.098867 0.000000 0.393519 0.888889 0.390266 0.104071 0.000000 0.393519 0.933333 0.390266 0.109275 0.000000 0.393519 0.977778 0.390266 0.114478 0.000000 0.393519 1.022222 0.390266 0.119682 0.000000 0.393519 1.066667 0.390266 0.124885 0.000000 0.393519 1.111111 0.390266 0.130089 0.000000 0.393519 1.155556 0.390266 0.135292 0.000000 0.393519 1.200000 0.390266 0.140496 0.000000 0.393519 1.244444 0.390266 0.145699 0.000000 0.393519 1.288889 0.390266 0.150903 0.000000 0.393519 1.333333 0.390266 0.156107 0.000000 0.393519 1.377778 0.390266 0.161310 0.000000 0.393519 1.422222 0.390266 0.166514 0.000000 0.393519 1.466667 0.390266 0.171717 0.000000 0.393519 1.511111 0.390266 0.176921 0.000000 0.393519 1.555556 0.390266 0.182124 0.000000 0.393519 1.600000 0.390266 0.187328 0.000000 0.393519 1.644444 0.390266 0.192531 0.000000 0.393519 1.688889 0.390266 0.197735 0.000000 0.393519 1.733333 0.390266 0.202938 0.000000 0.393519 1.777778 0.390266 0.208142 0.000000 0.393519 1.822222 0.390266 0.213346 0.000000 0.393519 1.866667 0.390266 0.218549 0.000000 0.393519 1.911111 0.390266 0.223753 0.000000 0.393519 1.955556 0.390266 0.228956 0.000000 0.393519 2.000000 0.390266 0.234160 0.000000 0.393519 2.044444 0.390266 0.239363 0.000000 0.393519 2.088889 0.390266 0.244567 0.000000 0.393519 2.133333 0.390266 0.249770 0.000000 0.393519 2.177778 0.390266 0.254974 0.000000 0.393519 2.222222 0.390266 0.260178 0.000000 0.393519 2.266667 0.390266 0.265381 0.000000 0.393519 2.311111 0.390266 0.270585 0.000000 0.393519 2.355556 0.390266 0.275788 0.000000 0.393519 2.400000 0.390266 0.280992 0.000000 0.393519 2.444444 0.390266 0.286195 0.000000 0.393519 2.488889 0.390266 0.291399 0.000000 0.393519 2.533333 0.390266 0.296602 0.000000 0.393519 2.577778 0.390266 0.301806 0.000000 0.393519 2.622222 0.390266 0.307009 0.000000 0.393519 2.666667 0.390266 0.312213 0.000000 0.393519 2.711111 0.390266 0.317417 0.000000 0.393519 2.755556 0.390266 0.322620 0.000000 0.393519 2.800000 0.390266 0.327824 0.000000 0.393519 2.844444 0.390266 0.333027 0.000000 0.393519 2.888889 0.390266 0.338231 0.000000 0.393519 2.933333 0.390266 0.343434 0.000000 0.393519 2.977778 0.390266 0.348638 0.000000 0.393519 3.022222 0.390266 0.365983 0.035147 0.393519 3.066667 0.390266 0.383328 0.182234 0.393519 3.111111 0.390266 0.400673 0.389839 0.393519 3.155556 0.390266 0.418019 0.637321 0.393519 3.200000 0.390266 0.435364 0.907676 0.393519 3.244444 0.390266 0.452709 1.183559 0.393519 3.288889 0.390266 0.470054 1.447495 0.393519 3.333333 0.390266 0.487399 1.683468 0.393519 3.377778 0.390266 0.504744 1.879270 0.393519 3.422222 0.390266 0.522090 2.029388 0.393519 3.466667 0.390266 0.539435 2.138326 0.393519 One North Basin_12-22-20 12/22/2020 3:53:35 PM Page 27 3.511111 0.390266 0.556780 2.251735 0.393519 3.555556 0.390266 0.574125 2.347596 0.393519 3.600000 0.390266 0.591470 2.439693 0.393519 3.644444 0.390266 0.608815 2.528438 0.393519 3.688889 0.390266 0.626161 2.614172 0.393519 3.733333 0.390266 0.643506 2.697182 0.393519 3.777778 0.390266 0.660851 2.777713 0.393519 3.822222 0.390266 0.678196 2.855973 0.393519 3.866667 0.390266 0.695541 2.932146 0.393519 3.911111 0.390266 0.712886 3.006389 0.393519 3.955556 0.390266 0.730232 3.078843 0.393519 4.000000 0.390266 0.747577 3.149630 0.393519 4.044444 0.390266 0.764922 3.218861 0.393519 END FTABLE 3 END FTABLES EXT SOURCES <-Volume-> <Member> SsysSgap<--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # tem strg<-factor->strg <Name> # # <Name> # # *** WDM 2 PREC ENGL 0.857 PERLND 1 999 EXTNL PREC WDM 2 PREC ENGL 0.857 IMPLND 1 999 EXTNL PREC WDM 1 EVAP ENGL 0.76 PERLND 1 999 EXTNL PETINP WDM 1 EVAP ENGL 0.76 IMPLND 1 999 EXTNL PETINP WDM 2 PREC ENGL 0.857 RCHRES 1 EXTNL PREC WDM 2 PREC ENGL 0.857 RCHRES 3 EXTNL PREC WDM 1 EVAP ENGL 0.5 RCHRES 1 EXTNL POTEV WDM 1 EVAP ENGL 0.76 RCHRES 2 EXTNL POTEV END EXT SOURCES EXT TARGETS <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Volume-> <Member> Tsys Tgap Amd *** <Name> # <Name> # #<-factor->strg <Name> # <Name> tem strg strg*** RCHRES 3 HYDR RO 1 1 1 WDM 1018 FLOW ENGL REPL RCHRES 3 HYDR O 1 1 1 WDM 1019 FLOW ENGL REPL RCHRES 3 HYDR O 2 1 1 WDM 1020 FLOW ENGL REPL RCHRES 3 HYDR STAGE 1 1 1 WDM 1021 STAG ENGL REPL COPY 1 OUTPUT MEAN 1 1 48.4 WDM 701 FLOW ENGL REPL COPY 501 OUTPUT MEAN 1 1 48.4 WDM 801 FLOW ENGL REPL END EXT TARGETS MASS-LINK <Volume> <-Grp> <-Member-><--Mult--> <Target> <-Grp> <-Member->*** <Name> <Name> # #<-factor-> <Name> <Name> # #*** MASS-LINK 2 PERLND PWATER SURO 0.083333 RCHRES INFLOW IVOL END MASS-LINK 2 MASS-LINK 3 PERLND PWATER IFWO 0.083333 RCHRES INFLOW IVOL END MASS-LINK 3 MASS-LINK 5 IMPLND IWATER SURO 0.083333 RCHRES INFLOW IVOL END MASS-LINK 5 MASS-LINK 7 RCHRES OFLOW OVOL 1 RCHRES INFLOW IVOL END MASS-LINK 7 MASS-LINK 8 RCHRES OFLOW OVOL 2 RCHRES INFLOW IVOL END MASS-LINK 8 MASS-LINK 12 PERLND PWATER SURO 0.083333 COPY INPUT MEAN END MASS-LINK 12 MASS-LINK 13 PERLND PWATER IFWO 0.083333 COPY INPUT MEAN One North Basin_12-22-20 12/22/2020 3:53:35 PM Page 28 END MASS-LINK 13 MASS-LINK 15 IMPLND IWATER SURO 0.083333 COPY INPUT MEAN END MASS-LINK 15 MASS-LINK 17 RCHRES OFLOW OVOL 1 COPY INPUT MEAN END MASS-LINK 17 END MASS-LINK END RUN One North Basin_12-22-20 12/22/2020 3:53:35 PM Page 29 Predeveloped HSPF Message File One North Basin_12-22-20 12/22/2020 3:53:35 PM Page 30 Mitigated HSPF Message File One North Basin_12-22-20 12/22/2020 3:53:35 PM Page 31 Disclaimer Legal Notice This program and accompanying documentation are provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by : Clear Creek Solutions, Inc. 2005-2020; All Rights Reserved. Clear Creek Solutions, Inc. 6200 Capitol Blvd. Ste F Olympia, WA. 98501 Toll Free 1(866)943-0304 Local (360)943-0304 www.clearcreeksolutions.com ATTACHMENT I NRCS Geotechnical Web Soil Survey Soil Map—Thurston County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 12/7/2020 Page 1 of 351996805199730519978051998305199880519993051999805200030520008052001305199680519973051997805199830519988051999305199980520003052000805200130530290530340530390530440530490530540530590 530290 530340 530390 530440 530490 530540 530590 530640 46° 57' 14'' N 122° 36' 7'' W46° 57' 14'' N122° 35' 50'' W46° 56' 59'' N 122° 36' 7'' W46° 56' 59'' N 122° 35' 50'' WN Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS84 0 100 200 400 600Feet 0 30 60 120 180Meters Map Scale: 1:2,310 if printed on A portrait (8.5" x 11") sheet. Soil Map may not be valid at this scale. MAP LEGEND MAP INFORMATION Area of Interest (AOI) Area of Interest (AOI) Soils Soil Map Unit Polygons Soil Map Unit Lines Soil Map Unit Points Special Point Features Blowout Borrow Pit Clay Spot Closed Depression Gravel Pit Gravelly Spot Landfill Lava Flow Marsh or swamp Mine or Quarry Miscellaneous Water Perennial Water Rock Outcrop Saline Spot Sandy Spot Severely Eroded Spot Sinkhole Slide or Slip Sodic Spot Spoil Area Stony Spot Very Stony Spot Wet Spot Other Special Line Features Water Features Streams and Canals Transportation Rails Interstate Highways US Routes Major Roads Local Roads Background Aerial Photography The soil surveys that comprise your AOI were mapped at 1:24,000. Warning: Soil Map may not be valid at this scale. Enlargement of maps beyond the scale of mapping can cause misunderstanding of the detail of mapping and accuracy of soil line placement. The maps do not show the small areas of contrasting soils that could have been shown at a more detailed scale. Please rely on the bar scale on each map sheet for map measurements. Source of Map: Natural Resources Conservation Service Web Soil Survey URL: Coordinate System: Web Mercator (EPSG:3857) Maps from the Web Soil Survey are based on the Web Mercator projection, which preserves direction and shape but distorts distance and area. A projection that preserves area, such as the Albers equal-area conic projection, should be used if more accurate calculations of distance or area are required. This product is generated from the USDA-NRCS certified data as of the version date(s) listed below. Soil Survey Area: Thurston County Area, Washington Survey Area Data: Version 14, Jun 4, 2020 Soil map units are labeled (as space allows) for map scales 1:50,000 or larger. Date(s) aerial images were photographed: Mar 29, 2016—Oct 10, 2016 The orthophoto or other base map on which the soil lines were compiled and digitized probably differs from the background imagery displayed on these maps. As a result, some minor shifting of map unit boundaries may be evident. Soil Map—Thurston County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 12/7/2020 Page 2 of 3 Map Unit Legend Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 110 Spanaway gravelly sandy loam, 0 to 3 percent slopes 17.0 74.7% 111 Spanaway gravelly sandy loam, 3 to 15 percent slopes 5.8 25.3% Totals for Area of Interest 22.8 100.0% Soil Map—Thurston County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 12/7/2020 Page 3 of 3 Thurston County Area, Washington 110—Spanaway gravelly sandy loam, 0 to 3 percent slopes Map Unit Setting National map unit symbol: 2ndb6 Elevation: 330 to 1,310 feet Mean annual precipitation: 35 to 65 inches Mean annual air temperature: 50 degrees F Frost-free period: 150 to 200 days Farmland classification: Prime farmland if irrigated Map Unit Composition Spanaway and similar soils:100 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Spanaway Setting Landform:Terraces, outwash plains Parent material:Volcanic ash over gravelly outwash Typical profile H1 - 0 to 15 inches: gravelly sandy loam H2 - 15 to 20 inches: very gravelly loam H3 - 20 to 60 inches: extremely gravelly sand Properties and qualities Slope:0 to 3 percent Depth to restrictive feature:More than 80 inches Drainage class:Somewhat excessively drained Capacity of the most limiting layer to transmit water (Ksat):High (1.98 to 5.95 in/hr) Depth to water table:More than 80 inches Frequency of flooding:None Frequency of ponding:None Available water capacity:Low (about 3.8 inches) Interpretive groups Land capability classification (irrigated): 3s Land capability classification (nonirrigated): 3s Hydrologic Soil Group: A Forage suitability group: Droughty Soils (G002XS401WA) Other vegetative classification: Droughty Soils (G002XS401WA) Hydric soil rating: No Data Source Information Soil Survey Area: Thurston County Area, Washington Survey Area Data: Version 14, Jun 4, 2020 Map Unit Description: Spanaway gravelly sandy loam, 0 to 3 percent slopes---Thurston County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 12/7/2020 Page 1 of 1 Thurston County Area, Washington 111—Spanaway gravelly sandy loam, 3 to 15 percent slopes Map Unit Setting National map unit symbol: 2ndb7 Elevation: 330 to 1,310 feet Mean annual precipitation: 35 to 65 inches Mean annual air temperature: 50 degrees F Frost-free period: 150 to 200 days Farmland classification: Farmland of statewide importance Map Unit Composition Spanaway and similar soils:100 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Spanaway Setting Landform:Terraces, outwash plains Parent material:Volcanic ash over gravelly outwash Typical profile H1 - 0 to 15 inches: gravelly sandy loam H2 - 15 to 20 inches: very gravelly sandy loam H3 - 20 to 60 inches: extremely gravelly sand Properties and qualities Slope:3 to 15 percent Depth to restrictive feature:More than 80 inches Drainage class:Somewhat excessively drained Capacity of the most limiting layer to transmit water (Ksat):High (1.98 to 5.95 in/hr) Depth to water table:More than 80 inches Frequency of flooding:None Frequency of ponding:None Available water capacity:Low (about 3.8 inches) Interpretive groups Land capability classification (irrigated): 4s Land capability classification (nonirrigated): 4s Hydrologic Soil Group: A Forage suitability group: Droughty Soils (G002XS401WA) Other vegetative classification: Droughty Soils (G002XS401WA) Hydric soil rating: No Data Source Information Soil Survey Area: Thurston County Area, Washington Survey Area Data: Version 14, Jun 4, 2020 Map Unit Description: Spanaway gravelly sandy loam, 3 to 15 percent slopes---Thurston County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 12/7/2020 Page 1 of 1 Attachment J Site Plan, TESC and Drainage Plan 3 3 7 3383353363373323333343293313283283283333343353 3 6 32933133232 8 328329327328337338338335336337331332333334329328330330330TSTSTSTSTSTSTSTSTSTSTSTSTSTSTSTSTBTBTBTBTBTBTBTBTBTBTBTBTBTBTBTBX X X X X X X AS BUILT CENTERLINEGRAVEL DRIVEWAY DISTU R B E D D R I V E W A Y 40" FIR 27" FIR40" FIR 18" FIR 46" FIR 28" FIR 30" FIR 11" FIR 21" FIR 28" FIR 24" FIR 26" FIR 30" FIR 32" FIR 22" FIR 48" FIR 28" FIR 24" FIR 28" FIR 20" FIR 26" FIR 19" FIR 28" FIR 16" FIR 16" FIR22" FIR 22" FIR 24" FIR 32" FIR 15" FIR 15" FIR RHOTON ROADS 89°28'57" W 2653.34' S 89°53'29" W 418.30'258.35 ' 2294.54'240.00'N 00°06'31" W2644.20'17 2019 18 TR 17N 02 19 ETHURSTON COUNTYPARCEL NO.64300800301.1102 RHOTON RD SE LOT 1SS-00-8255-YL FOUND 5/8" REBAR W/ CAP LS 24227 FOUND 1/2" REBAR W/ PUSHED OVER CAP FOUND 1/2" REBAR W/ PUSHED OVER CAP PP FOUND 5/8" REBAR W/ CAP LS 24227 30' NE CORNER OF SECTION 19CALCULATED PER SURVEYREFERENCE 1 CENTER 1/4 CORNER OF SECTION 19 FOUND CASED MONUMENT W/ 2" BRASS DISC W/ PUNCH LS 22346 N 1/4 CORNER OF SECTION 19 FOUND 1/2" IRON PIPE W/MPK BENCH MARK = 328.82'S 20 °22 '43" E AIL MEADOWS CT SE 46 QUAIL MEADOW CT SE 04 RHOTON CT NW 45 QUAIL MEADOW CT SE 22718430300 9246 RHOTON RD 64300800302 1002 RHOTON RD SE RHOTON ROADCULLENSROADKILLIONROADIIIIIIIIIIIIIIIIIC A N A L R O A D C A N A L R O A D SITE YELM CENT R A L I A CANA L YEL M C R E E K 5016 Lacey Boulevard SE, Lacey, Washington 98503(360) 491-3399 Fax (360) 491-3857 YELM WA 1102 & 1002 RHOTON RD SE YELM, WA 98597 SITE PLAN, DRAINAGE, AND TESC TPN 64300800301 & 64300800302 Attachment K Onsite Stormwater Management BMPs 12/21/2020 BMP T5.13: Post-Construction Soil Quality and Depth https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/MiscLIDBMPs/BMPt513.htm%3FTocPat…1/3 You are here: 2019 SWMMWW > Volume V - Runoff Treatment, Flow Control, and LID BMP Library > V-11 Miscellaneous LID BMPs > BMP T5.13: Post-Construction Soil Quality and Depth BMP T5.13: Post-Construction Soil Quality and Depth Purpose and Definition Naturally occurring (undisturbed) soil and vegetation provide important stormwater functions including: water infiltration; nutrient, sediment, and pollutant adsorption; sediment and pollutant biofiltration; water interflow storage and transmission; and pollutant decomposition. These functions are largely lost when development strips away native soil and vegetation and replaces it with minimal topsoil and sod. Not only are these important stormwater functions lost, but such landscapes themselves become pollution generating pervious surfaces due to increased use of pesticides, fertilizers and other landscaping and household/industrial chemicals, the concentration of pet wastes, and pollutants that accompany roadside litter. Establishing soil quality and depth regains greater stormwater functions in the post development landscape, provides increased treatment of pollutants and sediments that result from development and habitation, and minimizes the need for some landscaping chemicals, thus reducing pollution through prevention. Applications and Limitations Establishing a minimum soil quality and depth is not the same as preservation of naturally occurring soil and vegetation. However, establishing a minimum soil quality and depth will provide improved on-site management of stormwater flow and water quality. Soil organic matter can be attained through numerous materials such as compost, composted woody material, biosolids, and forest product residuals. It is important that the materials used to meet this BMP be appropriate and beneficial to the plant cover to be established. Likewise, it is important that imported topsoils improve soil conditions and do not have an excessive percent of clay fines. This BMP can be considered infeasible on till soil slopes greater than 33 percent. Design Guidelines Soil Retention Retain, in an undisturbed state, the duff layer and native topsoil to the maximum extent practicable. In any areas requiring grading, remove and stockpile the duff layer and topsoil on site in a designated, controlled area, not adjacent to public resources and critical areas, to be reapplied to other portions of the site where feasible. Soil Quality All areas subject to clearing and grading that have not been covered by impervious surface, incorporated into a drainage facility or engineered as structural fill or slope shall, at project completion, demonstrate the following: 12/21/2020 BMP T5.13: Post-Construction Soil Quality and Depth https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/MiscLIDBMPs/BMPt513.htm%3FTocPat…2/3 1. A topsoil layer with a minimum organic matter content of 10% dry weight in planting beds, and 5% organic matter content in turf areas, and a pH from 6.0 to 8.0 or matching the pH of the undisturbed soil. The topsoil layer shall have a minimum depth of eight inches except where tree roots limit the depth of incorporation of amendments needed to meet the criteria. Subsoils below the topsoil layer should be scarified at least 4 inches with some incorporation of the upper material to avoid stratified layers, where feasible. 2. Mulch planting beds with 2 inches of organic material. 3. Use compost and other materials that meet the following organic content requirements: a. The organic content for “pre-approved” amendment rates can be met only using compost meeting the compost specification for BMP T7.30: Bioretention, with the exception that the compost may have up to 35% biosolids or manure. The compost must also have an organic matter content of 40% to 65%, and a carbon to nitrogen ratio below 25:1. The carbon to nitrogen ratio may be as high as 35:1 for plantings composed entirely of plants native to the Puget Sound Lowlands region. b. Calculated amendment rates may be met through use of composted material meeting (a.) above; or other organic materials amended to meet the carbon to nitrogen ratio requirements, and not exceeding the contaminant limits identified in Table 220-B, Testing Parameters, in WAC 173-350-220. The resulting soil should be conducive to the type of vegetation to be established. Implementation Options The soil quality design guidelines listed above can be met by using one of the methods listed below: 1. Leave undisturbed native vegetation and soil, and protect from compaction during construction. 2. Amend existing site topsoil or subsoil either at default “pre-approved” rates, or at custom calculated rates based on tests of the soil and amendment. 3. Stockpile existing topsoil during grading, and replace it prior to planting. Stockpiled topsoil must also be amended if needed to meet the organic matter or depth requirements, either at a default “pre- approved” rate or at a custom calculated rate. 4. Import topsoil mix of sufficient organic content and depth to meet the requirements. More than one method may be used on different portions of the same site. Soil that already meets the depth and organic matter quality standards, and is not compacted, does not need to be amended. Planning/Permitting/Inspection/Verification Guidelines & Procedures 12/21/2020 BMP T5.13: Post-Construction Soil Quality and Depth https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/MiscLIDBMPs/BMPt513.htm%3FTocPat…3/3 Local governments are encouraged to adopt guidelines and procedures similar to those recommended in Building Soil: Guidelines and Resources for Implementing Soil Quality and Depth BMP T5.13 in WDOE Stormwater Management Manual for Western Washington (Stenn et al., 2016). Maintenance Establish soil quality and depth toward the end of construction and once established, protect from compaction, such as from large machinery use, and from erosion. Plant vegetation and mulch the amended soil area after installation. Leave plant debris or its equivalent on the soil surface to replenish organic matter. Reduce and adjust, where possible, the use of irrigation, fertilizers, herbicides and pesticides, rather than continuing to implement formerly established practices. Runoff Model Representation All areas meeting the soil quality and depth design criteria may be entered into approved runoff models as “Pasture” rather than “Lawn/Landscaping”. Figure V-11.1: Planting Bed Cross-Section pdf download Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 D EPARTMENT OF ECOLOGY State of Washington Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. Planting Bed Cross-Section Revised June 2016 NOT TO SCALE Mulch Loose soil with visible dark organic matter Loose or fractured subsoil 4" 8" Reprinted from Guidelines and Resources For Implementing Soil Quality and Depth BMP T5.13 in WDOE Stormwater Management Manual for Western Washington, 2010, Washington Organic Recycling Council 12/21/2020 BMP T5.40: Preserving Native Vegetation https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/SiteDesignBMPs/BMPt540.htm%3FTocP…1/2 You are here: 2019 SWMMWW > Volume V - Runoff Treatment, Flow Control, and LID BMP Library > V-2 Site Design BMPs > BMP T5.40: Preserving Native Vegetation BMP T5.40: Preserving Native Vegetation Purpose and Definition Preserving native vegetation on-site to the maximum extent practicable will minimize the impacts of development on stormwater runoff. Preferably 65 percent or more of the development site should be protected for the purposes of retaining or enhancing existing forest cover and preserving wetlands and stream corridors. Maintain tree canopy on the project site to the greatest extent feasible and in accordance with the requirements of the local jurisdiction. Applications and Limitations New development often takes place on tracts of forested land. In fact, building sites are often selected because of the presence of mature trees. However, unless sufficient care is taken and planning done, in the interval between buying the property and completing construction much of this resource is likely to be destroyed. The property owner is ultimately responsible for protecting as many trees as possible, with their understory and groundcover. This responsibility is usually exercised by agents, the planners, designers and contractors. It takes 20 to 30 years for newly planted trees to provide the benefits for which trees are so highly valued. Forest and native growth areas allow rainwater to naturally percolate into the soil, recharging ground water for summer stream flows and reducing surface water runoff that creates erosion and flooding. Conifers can hold up to about 50 percent of all rain that falls during a storm. Twenty to 30 percent of this rain may never reach the ground but evaporates or is taken up by the tree. Forested and native growth areas also may be effective as stormwater buffers around smaller developments. Preservation of 65 percent or more of the site in native vegetation will allow the use of full dispersion techniques presented in BMP T5.30: Full Dispersion. Sites that can fully disperse per BMP T5.30: Full Dispersion have met the requirements of I-3.4.5 MR5: On-Site Stormwater Management, I-3.4.6 MR6: Runoff Treatment, and I-3.4.7 MR7: Flow Control. Design Guidelines The preserved area should be situated to minimize the clearing of existing forest cover, to maximize the preservation of wetlands, and to buffer stream corridors. The preserved area should be placed in a separate tract or protected through recorded easements for individual lots. If feasible, the preserved area should be located downslope from the building sites, since flow control and runoff treatment are enhanced by flow dispersion through duff, undisturbed soils, and native vegetation. 12/21/2020 BMP T5.40: Preserving Native Vegetation https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/SiteDesignBMPs/BMPt540.htm%3FTocP…2/2 The preserved area should be shown on all property maps and should be clearly marked during clearing and construction on the site. Maintenance Vegetation and trees should not be removed from the natural growth retention area, except for approved timber harvest activities and the removal of dangerous and diseased trees. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 12/21/2020 BMP T7.20: Infiltration Trenches https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt720.htm%3FTocP…1/4 You are here: 2019 SWMMWW > Volume V - Runoff Treatment, Flow Control, and LID BMP Library > V-5 Infiltration BMPs > BMP T7.20: Infiltration Trenches BMP T7.20: Infiltration Trenches Infiltration trenches are generally at least 24 inches wide, and are backfilled with a coarse stone aggregate, allowing for temporary storage of stormwater runoff in the voids of the aggregate material. Stored runoff then gradually infiltrates into the surrounding soil. The surface of the trench can be covered with grating and/or consist of stone, gabion, sand, or a grassed or asphalt area with a surface inlet. Perforated rigid pipe of at least 8-inch diameter can also be used to distribute the stormwater in an infiltration trench. Underground Injection Control (UIC) regulations apply to infiltration trenches when perforated pipe is used, and then, provided that the design, operation, and maintenance criteria in this section are met, only the registration requirement applies. Where perforated pipe is not used, the registration requirement does not apply. See I-4 UIC Program for details. If this BMP is proposed to be used for Runoff Treatment, the design must show that the criteria for Runoff Treatment in V-5.6 Site Suitability Criteria (SSC) are met. Refer to the guidance earlier in this chapter for information pertinent to all infiltration BMPs. Guidance specific to infiltration trenches is provided below. Figure V-5.5: Schematic of an Infiltration Trench pdf download Figure V-5.6: Parking Lot Perimeter Trench Design pdf download Figure V-5.7: Median Strip Trench Design 12/21/2020 BMP T7.20: Infiltration Trenches https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt720.htm%3FTocP…2/4 pdf download Figure V-5.8: Oversized Pipe Trench Design pdf download Figure V-5.9: Swale/Trench Design pdf download Figure V-5.10: Underground Trench with Oil/Grit Chamber pdf download Design Criteria Due to accessibility and maintenance limitations, carefully design and construct infiltration trenches. Contact the local jurisdiction for additional specifications. Consider including an access port or open or grated top for accessibility to conduct inspections and maintenance. Backfill Material - The aggregate material for the infiltration trench should consist of a clean aggregate with a maximum diameter of 3 inches and a minimum diameter of 1.5 inches. Void space for these aggregates should be in the range of 30 to 40 percent. Geotextile fabric liner – Completely encase the aggregate fill material in an engineering geotextile material. Geotextile should surround all of the aggregate fill material except for the top one-foot, which is placed over the geotextile. Carefully select geotextile fabric with acceptable properties to avoid plugging (see V-1.3.4 Geotextile Specifications). The bottom sand or geotextile fabric as shown in Figure V-5.11: Observation Well Details is optional. 12/21/2020 BMP T7.20: Infiltration Trenches https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt720.htm%3FTocP…3/4 Refer to the Geosynthetic Design and Construction Guidelines Participant Notebook (Holtz et al., 1998) for design guidance on geotextiles in drainage applications. Refer to Long-Term Performance of Geosynthetics in Drainage Applications (Koerner et al., 1994) for long-term performance data and background on the potential for geotextiles to clog, blind, or to allow piping to occur and how to design for these issues. Overflow Channel - Because an infiltration trench is generally used for small drainage areas, an emergency spillway is not necessary. However, provide a non-erosive overflow channel leading to a stabilized watercourse. Surface Cover - A stone filled trench can be placed under a porous or impervious surface cover to conserve space. Observation Well - Install an observation well at the lower end of the infiltration trench to check water levels, drawdown time, sediment accumulation, and conduct water quality monitoring. Figure V-5.11: Observation Well Details illustrates observation well details. It should consist of a perforated PVC pipe which is 4 to 6 inches in diameter and it should be constructed flush with the ground elevation. For larger trenches a 12-36 inch diameter well can be installed to facilitate maintenance operations such as pumping out the sediment. Cap the top of the well to discourage vandalism and tampering. Construction Criteria Trench Preparation - Place excavated materials away from the trench sides to enhance trench wall stability. Take care to keep this material away from slopes, neighboring property, sidewalks and streets. It is recommended that this material be covered with plastic. (See BMP C123: Plastic Covering). Stone Aggregate Placement and Compaction - Place stone aggregate in lifts and compact using plate compactors. In general, a maximum loose lift thickness of 12 inches is recommended. The compaction process ensures geotextile conformity to the excavation sides, thereby reducing potential piping and geotextile clogging, and settlement problems. Potential Contamination - Prevent natural or fill soils from intermixing with the stone aggregate. Remove all contaminated stone aggregate and replaced with uncontaminated stone aggregate. Overlapping and Covering - Following the stone aggregate placement, fold the geotextile over the stone aggregate to form a 12 inch minimum longitudinal overlap. When overlaps are required between rolls, the upstream roll should overlap a minimum of 2 feet over the downstream roll in order to provide a shingled effect. Voids behind Geotextile - Voids between the geotextile and excavation sides must be avoided. Removing boulders or other obstacles from the trench walls is one source of such voids. Place natural soils in these voids at the most convenient time during construction to ensure geotextile conformity to the excavation sides. This remedial process will avoid soil piping, geotextile clogging, and possible surface subsidence. Unstable Excavation Sites - Vertically excavated walls may be difficult to maintain in areas where the soil moisture is high or where soft or cohesionless soils predominate. Trapezoidal, rather than rectangular, cross-sections may be needed. 12/21/2020 BMP T7.20: Infiltration Trenches https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt720.htm%3FTocP…4/4 Maintenance Criteria Monitor sediment buildup in the top foot of stone aggregate or the surface inlet on the same schedule as the observation well. Figure V-5.11: Observation Well Details pdf download Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 Wellcap Observation well � W /. O O OW O O O W \W v �W .✓ � ✓ � W W W W Emergency overflow berm �W Runoff filters through 20 foot W W W y y W W W W wide grass buffer strip W Protective layer of filter fabric I 111111110 0 0 0 0 0 0 � Trench 3-8 feet deep filled with 1.5 - 2.5 inch diameter clean stone Runoff exfiltrates through undisturbed subsoils Filter fabric lines si prevent soil contan <iTlI Sand filter 6-12 inches deep or fabric equivalent NOT TO SCALE 810 "go*& Schematic of an Infiltration Trench DEPARTMENT OF Revised May 2019 ECOLOGY State of Washington D EPARTMENT OF ECOLOGY State of Washington Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. Parking Lot Perimeter Trench Design Revised June 2016 NOT TO SCALE Top View Side View Slope of parking lot Cars Berm (grassed)20' Grass filter stripSlotted curb spacers Storm drain Slotted curbs act as a level spreader Filter strip directly abuts pavement trench Dripline of tree should not extend over trench Optional sand filter Removable protective filter cloth layer D EPARTMENT OF ECOLOGY State of Washington Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. Median Strip Trench Design Revised June 2016 NOT TO SCALE Top View Side View Grass filter Trench Grass filter Screened overflow pipe Outflow 20' Grass filter strip Permeable filter fabric one foot below surface, traps debris 6 - 12 inch sand filter or permeable filter cloth lines bottom Clean washed stone or gravel (1.5 - 3.0 inch) Sides lined with permeable filter fabric Section View / Removable impermeable Overflow pipe Observation well Oversized Pipe (Temporarily stores runoff) Removable permeable Plan View /— Observation well 0_ Overflow pipe 1.5 - 3.0 inch clean stone Holes drilled in underside of pipe Note: Alternative storage devices, such as plastic arches, are also acceptable in place of oversized pipe. 1100 "cows DEPARTMENT OF ECOLOGY State of Washington Pretreatment facility Standard curb inlet Modified two -chamber inlet NOT TO SCALE Oversized Pipe Trench Design Revised May 2019 D EPARTMENT OF ECOLOGY State of Washington Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. Swale/Trench Design Revised June 2016 NOT TO SCALE Top View Side View Swale Driveway culvert Railroad tie check dam Driveway culvert SwaleDirection of flow Runoff Slope of the trench should be less than 5%RoadRunoff Permeable filter fabric lines sides and also at one foot trench depth 6 inch sand layer Exfiltration D EPARTMENT OF ECOLOGY State of Washington Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. Underground Trench with Oil/Grit Chamber Revised June 2016 NOT TO SCALE Top View Side View Stormdrain inlet Manholes for clean-out access Three-chamber water quality inlet Overflow pipe Perforated pipe inlet Underground trench 6 inch orifices Inverted elbow Overflow pipe Trash rack Impermeable filter cloth Test well 6 inch sand layer 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…1/25 You are here: 2019 SWMMWW > Volume V - Runoff Treatment, Flow Control, and LID BMP Library > V-5 Infiltration BMPs > BMP T7.30: Bioretention BMP T7.30: Bioretention Purpose Ecology accepts bioretention as having the potential to meet I-3.4.5 MR5: On-Site Stormwater Management, I- 3.4.6 MR6: Runoff Treatment and I-3.4.7 MR7: Flow Control for the tributary drainage areas depending upon site conditions and sizing. The purpose of bioretention is to provide effective removal of many stormwater pollutants, and provide reductions in stormwater runoff quantity and surface runoff flow rates. Where the surrounding native soils have adequate infiltration rates, bioretention can provide both Runoff Treatment and Flow Control. Where the native soils have low infiltration rates, underdrain systems can be installed and the bioretention BMP can still be used as a Runoff Treatment BMP. However, designs utilizing underdrains provide less Flow Control benefits. Description Bioretention areas are shallow landscaped depressions, with a designed soil mix (the bioretention soil mix) and plants adapted to the local climate and soil moisture conditions, that receive stormwater from a contributing area. Bioretention uses the imported bioretention soil mix as a treatment medium. As in infiltration, the pollutant removal mechanisms include filtration, adsorption, and biological action. Bioretention BMPs can be built within earthen swales or placed within vaults. Water that has passed through the bioretention soil mix (or approved equivalent) may be discharged to the ground or collected and discharged to surface water. The term, bioretention, is used to describe various designs using soil and plant complexes to manage stormwater. The following terminology is used in this manual: Bioretention cells: Shallow depressions with a designed planting soil mix and a variety of plant material, including trees, shrubs, grasses, and/or other herbaceous plants. Bioretention cells may or may not have an underdrain and are not designed as a conveyance system. Bioretention swales: Incorporate the same design features as bioretention cells; however, bioretention swales are designed as part of a system that can convey stormwater when maximum ponding depth is exceeded. Bioretention swales have relatively gentle side slopes and ponding depths that are typically 6 to 12 inches. Bioretention planters and planter boxes: Bioretention soil mix and a variety of plant material including trees, shrubs, grasses, and/or other herbaceous plants within a vertical walled container usually constructed from formed concrete, but could include other materials. Planter boxes are completely impervious and include a bottom (must include an underdrain). Planters have an open bottom and allow infiltration to the subgrade. These designs are often used in ultra-urban settings. 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…2/25 Stormwater planters in the ROW require urban design and tailoring it to street typology and context. NACTO Urban Street Stormwater Guide provides guidance for designing roadside stormwater planters. https://nacto.org/publication/urban-street-stormwater-guide/ See Figure V-5.12: Typical Bioretention, Figure V-5.13: Typical Bioretention w/Underdrain, Figure V-5.14: Typical Bioretention w/Liner (Not LID), and Figure V-5.15: Example of a Bioretention Planter for examples of various types of bioretention configurations. Note: Ecology has approved use of certain manufactured treatment devices that use specific, high rate media for treatment. Such systems do not use bioretention soil mix, and are not considered a bioretention BMP (even though marketing materials for these manufactured treatment devices may compare them to bioretention). See V- 10 Manufactured Treatment Devices as BMPs for more information on manufactured treatment devices. Figure V-5.12: Typical Bioretention pdf download Figure V-5.13: Typical Bioretention w/Underdrain pdf download Figure V-5.14: Typical Bioretention w/Liner (Not LID) pdf download Figure V-5.15: Example of a Bioretention Planter pdf download 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…3/25 Applications and Limitations Because bioretention BMPs use an imported soil mix that has a moderate design infiltration rate, they are best applied for small drainages, and near the source of the stormwater runoff. Bioretention cells may be scattered throughout a subdivision; a bioretention swale may run alongside the access road; or a series of bioretention planter boxes may serve the road. In these situations, they can but are not required to fully meet the requirement to treat 91% of the stormwater runoff file (the Water Quality Design Volume, as described in III-2.6 Sizing Your Runoff Treatment BMPs) from pollution-generating surfaces. The amount of stormwater that is predicted to pass through the bioretention soil mix is treated, and may be subtracted from the 91% volume that must be treated to meet I-3.4.6 MR6: Runoff Treatment. Downstream Runoff Treatment BMPs may be significantly smaller as a result. Bioretention BMPs that infiltrate into the ground can also provide significant Flow Control. They can, but are not required to fully meet the Flow Control Performance Standard of I-3.4.7 MR7: Flow Control. Because they typically do not have an orifice restricting overflow or underflow discharge rates, they typically don’t fully meet I-3.4.7 MR7: Flow Control. However, their performance contributes to meeting the standard, and that can result in much smaller additional Flow Control BMPs at the bottom of the project site. Bioretention can also help achieve compliance with the LID Performance Standard of I-3.4.5 MR5: On-Site Stormwater Management. Bioretention constructed with imported composted material should not be used within one-quarter mile of phosphorus-sensitive waterbodies if the underlying native soil does not meet the criteria for Runoff Treatment per V-5.6 Site Suitability Criteria (SSC). Preliminary monitoring indicates that new bioretention BMPs can add phosphorus to stormwater. Therefore, they should also not be used with an underdrain when the underdrain water would be routed to a phosphorus-sensitive receiving water. Applications with or without underdrains vary extensively and can be applied in new development, redevelopment and retrofits. Typical applications include: Individual lots for rooftop, driveway, and other on-lot impervious surfaces. Shared facilities located in common areas for individual lots. Areas within loop roads or cul-de-sacs. Landscaped parking lot islands. Within right-of-ways along roads (often linear bioretention swales or cells). Common landscaped areas in apartment complexes or other multifamily housing designs. Planters on building roofs, patios, and as part of streetscapes. Infeasibility Criteria The following infeasibility criteria describe conditions that make bioretention infeasible when applying The List Approach within I-3.4.5 MR5: On-Site Stormwater Management. If a project proponent wishes to use a 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…4/25 bioretention BMP even though one of the infeasibility criteria within this section are met,, they may propose a functional design to the local government. Criteria with setback distances are as measured from the bottom edge of the bioretention soil mix. Any of the following circumstances allow the designer to determine bioretention as "infeasible" when applying the The List Approach within I-3.4.5 MR5: On-Site Stormwater Management: Citation of any of the following infeasibility criteria must be based on an evaluation of site-specific conditions and a written recommendation from an appropriate licensed professional (e.g., engineer, geologist, hydrogeologist): Where professional geotechnical evaluation recommends infiltration not be used due to reasonable concerns about erosion, slope failure, or down gradient flooding. Within an area whose ground water drains into an erosion hazard, or landslide hazard area. Where the only area available for siting would threaten the safety or reliability of pre-existing underground utilities, pre-existing underground storage tanks, pre-existing structures, or pre-existing road or parking lot surfaces. Where the only area available for siting does not allow for a safe overflow pathway to the municipal separate storm sewer system or private storm sewer system. Where there is a lack of usable space for bioretention BMPs at re-development sites, or where there is insufficient space within the existing public right-of-way on public road projects. Where infiltrating water would threaten existing below grade basements. Where infiltrating water would threaten shoreline structures such as bulkheads. The following infeasibility criteria are based on conditions such as topography and distances to predetermined boundaries. Citation of the following criteria do not need site-specific written recommendations from a licensed professional, although some may require professional services to determine: Within setbacks from structures as established by the local government with jurisdiction. Where they are not compatible with the surrounding drainage system as determined by the local government with jurisdiction (e.g., project drains to an existing stormwater collection system whose elevation or location precludes connection to a properly functioning bioretention BMP). Where land for bioretention is within area designated as an erosion hazard or landslide hazard. Where the site cannot be reasonably designed to locate bioretention BMPs on slopes less than 8%. Within 50 feet from the top of slopes that are greater than 20% and over 10 feet of vertical relief. For properties with known soil or ground water contamination (typically federal Superfund sites or state cleanup sites under the Model Toxics Control Act (MTCA)): 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…5/25 Within 100 feet of an area known to have deep soil contamination; Where ground water modeling indicates infiltration will likely increase or change the direction of the migration of pollutants in the ground water; Wherever surface soils have been found to be contaminated unless those soils are removed within 10 horizontal feet from the infiltration area; Any area where these BMPs are prohibited by an approved cleanup plan under the state Model Toxics Control Act or Federal Superfund Law, or an environmental covenant under Chapter 64.70 RCW. Within 100 feet of a closed or active landfill. Within 100 feet of a drinking water well, or a spring used for drinking water supply. Within 10 feet of small on-site sewage disposal drainfield, including reserve areas, and grey water reuse systems. For setbacks from a “large on-site sewage disposal system”, see Chapter 246-272B WAC. Within 10 feet of an underground storage tank and connecting underground pipes when the capacity of the tank and pipe system is 1100 gallons or less. (As used in these criteria, an underground storage tank means any tank used to store petroleum products, chemicals, or liquid hazardous wastes of which 10% or more of the storage volume (including volume in the connecting piping system) is beneath the ground surface. Within 100 feet of an underground storage tank and connecting underground pipes when the capacity of the tank and pipe system is greater than 1100 gallons. Where the minimum vertical separation of 1 foot to the seasonal high water table, bedrock, or other impervious layer would not be achieved below bioretention that would serve a drainage area that is less than: 1. 5,000 sq. ft. of pollution-generating impervious surface, and 2. 10,000 sq. ft. of impervious surface, and 3. three-quarter (3/4) acres of pervious surface. Where the minimum vertical separation of 3 feet to the seasonal high water table, bedrock, or other impervious layer would not be achieved below bioretention that would serve a drainage area that meets or exceeds: 1. 5,000 sq. ft. of pollution-generating impervious surface, or 2. 10,000 sq. ft. of impervious surface, or 3. three-quarter (3/4) acres of pervious surface. AND 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…6/25 cannot reasonably be broken down into amounts smaller than those listed in 1-3 (above). Where the field testing indicates potential bioretention sites have a measured (a.k.a., initial) native soil saturated hydraulic conductivity less than 0.30 inches per hour. If the measured native soil infiltration rate is less than 0.30 in/hour, bioretention should not be used to meet the The List Approach of I-3.4.5 MR5: On-Site Stormwater Management. In these slow draining soils, a bioretention BMP with an underdrain may be used to treat pollution-generating surfaces to help meet I-3.4.6 MR6: Runoff Treatment. If the underdrain is elevated within a base course of gravel, the bioretention BMP will also provide some modest flow reduction benefit that will help achieve the LID Performance Standard within I-3.4.5 MR5: On-Site Stormwater Management and/or the Flow Control Performance Standard within I-3.4.7 MR7: Flow Control. A local government may designate geographic boundaries within which bioretention BMPs may be designated as infeasible due to year-round, seasonal or periodic high groundwater conditions, or due to inadequate infiltration rates. Designations must be based upon a pre-ponderance of field data, collected within the area of concern, that indicate a high likelihood of failure to achieve the minimum ground water clearance or infiltration rates identified in the above infeasibility criteria. The local government must develop a technical report and make it available upon request to Ecology. The report must be authored by (a) professional(s) with appropriate expertise (e.g., registered engineer, geologist, hydrogeologist, or certified soil scientist), and document the location and the pertinent values/observations of data that were used to recommend the designation and boundaries for the geographic area. The types of pertinent data include, but are not limited to: Standing water heights or evidence of recent saturated conditions in observation wells, test pits, test holes, and well logs. Observations of areal extent and time of surface ponding, including local government or professional observations of high water tables, frequent or long durations of standing water, springs, wetlands, and/or frequent flooding. Results of infiltration tests In addition, a local government can map areas that meet a specific infeasibility criterion listed above provided they have an adequate data basis. Criteria that are most amenable to mapping are: Where land for bioretention is within an area designated by the local government as an erosion hazard, or landslide hazard Within 50 feet from the top of slopes that are greater than 20% and over 10 feet vertical relief Within 100 feet of a closed or active landfill Design Criteria General Design Criteria 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…7/25 Utility conflicts: Consult local jurisdiction requirements for horizontal and vertical separation required for publicly-owned utilities, such as water and sewer. Consult the appropriate franchise utility owners for separation requirements from their utilities, which may include communications and gas. When separation requirements cannot be met, designs should include appropriate mitigation measures, such as impermeable liners over the utility, sleeving utilities, fixing known leaky joints or cracked conduits, and/or adding an underdrain to the bioretention. Transportation safety: The design configuration and selected plant types should provide adequate sight distances, clear zones, and appropriate setbacks for roadway applications in accordance with local jurisdiction requirements. Ponding depth and surface water draw-down: Flow Control needs, as well as location in the development, and mosquito breeding cycles will determine draw-down timing. For example, front yards and entrances to residential or commercial developments may require rapid surface dewatering for aesthetics. In no case shall draw down time exceed 48 hours. Impacts of surrounding activities: Human activity influences the location of the BMP in the development. For example, locate bioretention BMPs away from traveled areas on individual lots to prevent soil compaction and damage to vegetation or provide elevated or bermed pathways in areas where foot traffic is inevitable. Provide barriers, such as wheel stops, to restrict vehicle access in roadside applications. Visual buffering: Bioretention BMPs can be used to buffer structures from roads, enhance privacy among residences, and for an aesthetic site feature. Site growing characteristics and plant selection: Appropriate plants should be selected for sun exposure, soil moisture, and adjacent plant communities. Native species or hardy cultivars are recommended and can flourish in the properly designed and placed bioretention soil mix with no nutrient or pesticide inputs and 2-3 years irrigation for establishment. Invasive species and noxious weed control will be required as typical with all planted landscape areas. Project submission requirements: Submit the results of infiltration (Ksat) testing and ground water elevation testing (or other documentation and justification for the rates and hydraulic restriction layer clearances) with the Stormwater Site Plan as justification for the feasibility decision regarding bioretention and as justification for assumptions made in the runoff modeling. Legal documentation to track bioretention obligations: Where drainage plan submittals include assumptions with regard to size and location of bioretention BMPs, approval of the plat, short-plat, or building permit should identify the bioretention obligation of each lot; and the appropriate lots should have deed requirements for construction and maintenance of those BMPs Much of the design criteria within this BMP originated from the Low Impact Development Technical Guidance Manual for Puget Sound (Hinman and Wulkan, 2012). Refer to that document for additional explanations and background. Note that the Low Impact Development Technical Guidance Manual for Puget Sound (Hinman and Wulkan, 2012) is for additional information purposes only. You must follow the guidance within this manual if there 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…8/25 are any discrepancies between this manual and the Low Impact Development Technical Guidance Manual for Puget Sound (Hinman and Wulkan, 2012). Geotechnical analysis is an important first step to develop an initial assessment of the variability of site soils, infiltration characteristics and the necessary frequency and depth of infiltration tests. See V-5.2 Infiltration BMP Design Steps. Determining the Native Soil Infiltration Rates Determining infiltration rates of the site soils is necessary to determine feasibility of designs that intend to infiltrate stormwater on-site. It is also necessary to estimate flow reduction benefits of such designs when using a continuous runoff model. The certified soils professional or engineer can exercise discretion concerning the need for and extent of infiltration rate (saturated hydraulic conductivity, Ksat) testing. The professional can consider a reduction in the extent of infiltration (Ksat) testing if, in their judgment, information exists confirming that the site is unconsolidated outwash material with high infiltration rates, and there is adequate separation from ground water. The following provides recommended tests for the soils underlying bioretention BMPs. The test should be run at the anticipated elevation of the top of the native soil beneath the bioretention BMP. Refer to V-5.4 Determining the Design Infiltration Rate of the Native Soils for further guidance on the methods to determine the infiltration rate of the native soils. Small bioretention cells (bioretention BMPs made up of one or multiple cells that receive water from 1 or 2 individual lots or < 1/4 acre of pavement or other impervious surface) have the following options for determining the native soil infiltration rate: 1. Small-scale pilot infiltration test (PIT) as described in V-5.4 Determining the Design Infiltration Rate of the Native Soils. 2. If the site is underlain with soils not consolidated by glacial advance (e.g., recessional outwash soils), then the designer may use the grain size analysis method described in V-5.4 Determining the Design Infiltration Rate of the Native Soils based on the layer(s) identified in results of one soil test pit or boring. Large bioretention cells (bioretention BMPs made up of one or multiple cells that receive water from several lots or 1/4 acre or more of pavement or other impervious surface) have the following options for determining the native soil infiltration rate: 1. Multiple small-scale or one large-scale PIT. If using the small-scale test, measurements should be taken at several locations within the area of interest. 2. If the site is underlain with soils not consolidated by glacial advance (e.g., recessional outwash soils), then the designer may use the grain size analysis method described in V-5.4 Determining the Design Infiltration Rate of the Native Soils. Use the grain size analysis method based on more than one soil test pit or boring. The more test pits/borings used, and the more evidence of consistency in the soils, the less of a correction factor may be used. 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…9/25 Bioretention swales have the following options for determining the native soil infiltration rate: 1. Approximately 1 small-scale PIT per 200 feet of swale, and within each length of road with significant differences in subsurface characteristics. 2. If the site is underlain with soils not consolidated by glacial advance (e.g., recessional outwash soils), then the designer may use the grain size analysis method described in V-5.4 Determining the Design Infiltration Rate of the Native Soils. Approximately 1 soil test pit/boring per 200 feet of swale and within each length of road with significant differences in subsurface characteristics. On a single, smaller commercial property, one bioretention BMP will likely be appropriate. In that case, a small-scale PIT – or an alternative small scale test specified by the local government - should be performed at the proposed bioretention location. Tests at more than one site could reveal the advantages of one location over another. On larger commercial sites, a small-scale PIT every 5,000 sq. ft. is advisable. If soil characteristics across the site are consistent, a geotechnical professional may recommend a reduction in the number of tests. On multi-lot residential developments, multiple bioretention BMPs, or a BMP stretching over multiple properties are appropriate. In most cases, it is necessary to perform small-scale PITs, or other small-scale tests as allowed by the local jurisdiction. A test is advisable at each potential bioretention site. Long, narrow bioretention BMPs, such as one following the road right-of-way, should have a test location at least every 200 lineal feet, and within each length of road with significant differences in subsurface characteristics. If the site subsurface characterization, including soil borings across the development site, indicate consistent soil characteristics and depths to seasonal high ground water conditions or a hydraulic restriction layer, the number of test locations may be reduced to a frequency recommended by a geotechnical professional. After concluding an infiltration test, infiltration test sites should be over-excavated 3 feet below the projected bioretention BMP's bottom elevation unless minimum clearances to seasonal high ground water have or will be determined by another method. This overexcavation is to determine if there are restrictive layers or ground water. Observe whether water is infiltrating vertically or only spreading horizontally because of ground water or a restrictive soil layer. Observations through a wet season can identify a seasonal ground water restriction. If a single bioretention BMP serves a drainage area exceeding 1 acre, a ground water mounding analysis may be necessary in accordance with V-5.2 Infiltration BMP Design Steps. Assignment of Appropriate Correction Factors to the Native Soil If the design requires determination of a long-term (design) infiltration rate of the native soils (for example, to demonstrate compliance with the LID Performance Standard and/or the Flow Control Performance Standard), refer to V-5.4 Determining the Design Infiltration Rate of the Native Soils and the following additional guidance specific to bioretention BMPs: The overlying bioretention soil mix provides excellent protection for the underlying native soil from sedimentation. Accordingly, when using The Simplified Approach to Calculating the Design Infiltration Rate of the Native Soils as described in V-5.4 Determining the Design Infiltration Rate of the Native Soils, the 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…10/25 correction factor for the sub-grade soil does not have to take into consideration the extent of influent control and clogging over time. The correction factor to be applied to in-situ, small-scale infiltration test results for bioretention sites is determined by the site variability and number of locations tested as well as the method used to determine initial Ksat. Using Table V-5.1: Correction Factors to be Used With In-Situ Saturated Hydraulic Conductivity Measurements to Estimate Design Rates, the correction factor for bioretention design is revised based on this guidance as: Total Correction Factor, CFT = CFv x CFt Tests should be located and be at an adequate frequency capable of producing a soil profile characterization that fully represents the infiltration capability where the bioretention areas are to be located. The partial correction factor CFV depends on the level of uncertainty that variable subsurface conditions justify. If a pilot infiltration test is conducted for all bioretention areas or the range of uncertainty is low (for example, conditions are known to be uniform through previous exploration and site geological factors) one pilot infiltration test may be adequate to justify a CFV of one. If the level of uncertainty is high, a CFV near the low end of the range may be appropriate. Two example scenarios where low CFVs may be appropriate include: Site conditions are highly variable due to a deposit of ancient landslide debris, or buried stream channels. In these cases, even with many explorations and several pilot infiltration tests, the level of uncertainty may still be high. Conditions are variable, but few explorations and only one pilot infiltration test is conducted. That is, the number of explorations and tests conducted do not match the degree of site variability anticipated. Determining the Bioretention Soil Mix Design Infiltration Rate 1. Determine the initial saturated hydraulic conductivity (Ksat) based on the type of bioretention soil mix, as follows: If using Ecology's default bioretention soil mix (detailed below), the initial Ksat is 12 inches per hour (30.48 cm/hr). If using a custom bioretention soil mix (per the guidance for custom mixes below), use ASTM D 2434 Standard Test Method for Permeability of Granular Soils (Constant Head) with a compaction rate of 85 percent using ASTM D1557 Test Method for Laboratory Compaction Characteristics of Soil Using Modified Effort. See the additional guidance below for specific procedures for conducting ASTM D 2434. The designer must enter the derived Ksat value into the continuous modeling software. 2. After determining the initial Ksat, determine the appropriate safety factor: If the contributing area to the bioretention BMP is equal to or exceeds any of the following limitations: 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…11/25 5,000 square feet of pollution-generating impervious surface; 10,000 square feet of impervious surface; ¾ acre of lawn and landscape, use 4 as the Ksat safety factor. If the contributing area is less than all of the above areas, or if the design includes a pretreatment BMP for solids removal, use 2 as the Ksat safety factor. 3. The continuous runoff model has a field for entering Ksat and the appropriate safety factor. Recommended Modifications to ASTM D 2434 When Measuring Hydraulic Conductivity for Bioretention Soil Mixes Proctor method ASTM D1557 Method C (6-inch mold) shall be used to determine maximum dry density values for compaction of the bioretention soil sample. Sample preparation for the Proctor test shall be amended in the following ways: 1. Maximum grain size within the sample shall be no more than ½ inches in size. 2. Snip larger organic particles (if present) into1/2 inch long pieces. 3. When adding water to the sample during the Proctor test, allow the sample to pre-soak for at least 48 hours to allow the organics to fully saturate before compacting the sample. This pre-soak ensures the organics have been fully saturated at the time of the test. ASTM D2434 shall be used and amended in the following ways: 1. Apparatus: a. 6-inch mold size shall be used for the test. b. If using porous stone disks for the testing, the permeability of the stone disk shall be measured before and after the soil tests to ensure clogging or decreased permeability has not occurred during testing. c. Use the confined testing method, with 5- to 10-pound force spring d. Use de-aired water. 2. Sample: a. Maximum grain size within the sample shall not be more than ½ inch in size. b. Snip larger organic particles (if present) into ½-inch long pieces. c. Pre-soak the sample for at least 48 hours prior to loading it into the mold. During the pre- soak, the moisture content shall be higher than optimum moisture but less than full 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…12/25 saturation (i.e., there shall be no free water). This pre-soak ensures the organics have been fully saturated at the time of the test. 3. Preparation of Sample: a. Place soil in cylinder via a scoop. b. Place soil in 1-inch lifts and compact using a 2-inch-diameter round tamper. Pre-weigh how much soil is necessary to fill 1-inch lift at 85% of maximum dry density, then tamp to 1-inch thickness. Once mold is full, verify that density is at 85% of maximum dry density (+ or – 0.5%). Apply vacuum (20 inches Hg) for 15 minutes before inundation. c. Inundate sample slowly under a vacuum of 20 inches Hg over a period of 60 to 75 minutes. d. Slowly remove vacuum ( > 15 seconds). e. Sample shall be soaked in the mold for 24 to 72 hours before starting test. 4. Procedure: a. The permeability test shall be conducted over a range of hydraulic gradients between 0.1 and 2. b. Steady state flow rates shall be documented for four consecutive measurements before increasing the head. c. The permeability test shall be completed within one day (one-day test duration). Default Bioretention Soil Mix (BSM) Projects which use the following requirements for the bioretention soil mix do not have to test the mix for its saturated hydraulic conductivity (Ksat). See Determining the Bioretention Soil Mix Design Infiltration Rate. Mineral Aggregate for Default BSM Percent Fines: A range of 2 to 4 percent passing the #200 sieve is ideal and fines should not be above 5 percent for a proper functioning specification according to ASTM D422. Aggregate Gradation for Default BSM The aggregate portion of the BSM should be well-graded. According to ASTM D 2487-98 (Classification of Soils for Engineering Purposes (Unified Soil Classification System)), well-graded sand should have the following gradation coefficients: Coefficient of Uniformity (Cu = D60/D10) equal to or greater than 4, and Coefficient of Curve (Cc = (D30)2/D60 x D10) greater than or equal to 1 and less than or equal to 3. 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…13/25 Table V-5.2: General Guideline for Mineral Aggregate Gradation provides a gradation guideline for the aggregate component of the default bioretention soil mix (Hinman, 2009). The sand gradation below is often supplied as a well-graded utility or screened. With compost this blend provides enough fines for adequate water retention, hydraulic conductivity within recommended range (see below), pollutant removal capability, and plant growth characteristics for meeting design guidelines and objectives. Table V-5.2: General Guideline for Mineral Aggregate Gradation Sieve Size Percent Passing 3/8"100 #4 95-100 #10 75-90 #40 25-40 #100 4-10 #200 2-5 Where existing soils meet the above aggregate gradation, those soils may be amended rather than importing mineral aggregate. Compost to Aggregate Ratio, Organic Matter Content, and Cation Exchange Capacity for Default BSM Compost to aggregate ratio: 60-65 percent mineral aggregate, 35 – 40 percent compost by volume. Organic matter content: 5 – 8 percent by weight. Cation Exchange Capacity (CEC) must be > 5 milliequivalents/100 g dry soil Note: Soil mixes meeting the above specifications do not have to be tested for CEC. They will readily meet the minimum CEC. Compost for Default BSM To ensure that the BSM will support healthy plant growth and root development, contribute to biofiltration of pollutants, and not restrict infiltration when used in the proportions cited herein, the following compost standards are required. Meets the definition of “composted material” in WAC 173-350-100 and complies with testing parameters and other standards in WAC 173-350-220. Produced at a composting facility that is permitted by the jurisdictional health authority. Permitted compost facilities in Washington are included in a spreadsheet titled Washington composting facilities and material types – 2017 at the following web address: 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…14/25 https://ecology.wa.gov/Waste-Toxics/Reducing-recycling-waste/Organic-materials/Managing-organics- compost The compost product must originate a minimum of 65 percent by volume from recycled plant waste comprised of ”yard debris,” “crop residues,” and “bulking agents” as those terms are defined in WAC 173- 350-100. A maximum of 35 percent by volume of “post-consumer food waste” as defined in WAC 173-350- 100, but not including biosolids or manure, may be substituted for recycled plant waste. Stable (low oxygen use and CO2 generation) and mature (capable of supporting plant growth) by tests shown below. This is critical to plant success in bioretention soil mixes. Moisture content range: no visible free water or dust produced when handling the material. Tested in accordance with the U.S. Composting Council “Test Method for the Examination of Compost and Composting” (TMECC), as established in the Composting Council’s “Seal of Testing Assurance” (STA) program. Most Washington compost facilities now use these tests. Screened to the following size gradations for Fine Compost when tested in accordance with TMECC test method 02.02-B, Sample Sieving for Aggregate Size Classification.” Fine Compost shall meet the following gradation by dry weight Minimum percent passing 2”: 100% Minimum percent passing 1”: 99% Minimum percent passing 5/8”: 90% Minimum percent passing ¼”: 75% pH between 6.0 and 8.5 (TMECC 04.11-A). “Physical contaminants” (as defined in WAC 173-350-100) content less that 1% by weight (TMECC 03.08-A) total, not to exceed 0.25 percent film plastic by dry weight. Minimum organic matter content of 40% (TMECC 05.07-A “Loss on Ignition) Soluble salt content less than 4.0 dS/m (mmhos/cm) (TMECC 04.10-A “Electrical Conductivity, 1:5 Slurry Method, Mass Basis”) Maturity indicators from a cucumber bioassay (TMECC 05.05-A “Seedling Emergence and Relative Growth ) must be greater than 80%for both emergence and vigor”) Stability of 7 mg CO2-C/g OM/day or below (TMECC 05.08-B “Carbon Dioxide Evolution Rate”) Carbon to nitrogen ratio (TMECC 05.02A “Carbon to Nitrogen Ratio” which uses 04.01 “Organic Carbon” and 04.02D “Total Nitrogen by Oxidation”) of less than 25:1. The C:N ratio may be up to 35:1 for plantings composed entirely of Puget Sound Lowland native species and up to 40:1 for coarse compost to be used as a surface mulch (not in a soil mix). Custom Bioretention Soil Mix 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…15/25 Projects which prefer to create a custom bioretention soil mix rather than using the default bioretention soil mix described above must demonstrate compliance with the following criteria using the specified test method: CEC ≥ 5 meq/100 grams of dry soil; USEPA 9081 pH between 5.5 and 7.0 5 - 8 percent organic matter content before and after the saturated hydraulic conductivity test; ASTM D2974 (Standard Test Method for Moisture, Ash, and Organic Matter of Peat and Other Organic Soils) 2-5 percent fines passing the 200 sieve; TMECC 04.11-A Measured (Initial) saturated hydraulic conductivity (Ksat) of less than 12 inches per hour; ASTM D 2434 (Standard Test Method for Permeability of Granular Soils (Constant Head)) at 85% compaction per ASTM D 1557 (Standard Test Method s for Laboratory Compaction Characteristics of Soil Using Modified Effort). Also, use Recommended Modifications to ASTM D 2434 When Measuring Hydraulic Conductivity for Bioretention Soil Mixes (as detailed above). Design (long-term) saturated hydraulic conductivity of more than 1 inch per hour. Note: Design saturated hydraulic conductivity is determined by applying the appropriate infiltration correction factors as explained above under Determining the Bioretention Soil Mix Design Infiltration Rate. If compost is used in creating the custom bioretention soil mix, it must meet all of the specifications listed above in Compost for Default BSM, except for the gradation specification. An alternative gradation specification must indicate the minimum percent passing for a range of similar particle sizes. Flow Entrance and Presettling Flow entrance design will depend on topography, flow velocities and volume entering the pretreatment and bioretention area, adjacent land use and site constraints. Flow velocities entering bioretention should be less than 1.0 ft/second to minimize erosion potential. Flow entrances should be placed with adequate separation from outlets to ensure that the influent stormwater is treated prior to reaching the overflow. Five primary types of flow entrances can be used for bioretention: Dispersed, low velocity flow across a landscape area: Landscape areas and vegetated buffer strips slow incoming flows and provide an initial settling of particulates and are the preferred method of delivering flows to bioretention. Dispersed flow may not be possible given space limitations or if the BMP is controlling roadway or parking lot flows where curbs are mandatory. Dispersed or sheet flow across pavement or gravel and past wheel stops for parking areas. Curb cuts for roadside, driveway or parking lot areas: Curb cuts should include a rock pad, concrete or other erosion protection material in the channel entrance to dissipate energy. Minimum curb cut width should be 12 inches; however, 18 inches is recommended. The designer should calculate the size and choose the style of curb cut that is appropriate for the site conditions and runoff expectations. Avoid the use of angular rock or quarry spalls and instead use round (river) rock if needed. Removing sediment from angular rock is difficult. The flow entrance should slope steeply (at least 1:1) from the curb line to the bioretention, dropping 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…16/25 at least 3", and provide an area for settling and periodic removal of sediment and coarse material before flow dissipates to the remainder of the bioretention area. Curb cuts used for bioretention areas in high use parking lots or roadways require an increased level of maintenance due to high coarse particulates and trash accumulation in the flow entrance and associated bypass of flows. The following are methods recommended for areas where heavy trash and coarse particulates are anticipated: Curb cut width: 18 inches. At a minimum the flow entrance should drop 2 to 3 inches from the gutter line into the bioretention area and provide an area for settling and periodic removal of debris. Anticipate relatively more frequent inspection and maintenance for areas with large impervious areas, high traffic loads and larger debris loads. Catch basins or forebays may be necessary at the flow entrance to adequately capture debris and sediment load from large contributing areas and high use areas. Piped flow entrance in this setting can easily clog and catch basins with regular maintenance are necessary to capture coarse and fine debris and sediment. Pipe flow entrance: Piped entrances should include rock or other erosion protection material in the channel entrance to dissipate energy and disperse flow. Catch basin: In some locations where road sanding or higher than usual sediment inputs are anticipated, catch basins can be used to settle sediment and release water to the bioretention area through a grate for filtering coarse material. Trench drains: Trench drains can be used to cross sidewalks or driveways where a deeper pipe conveyance creates elevation problems. Trench drains tend to clog and may require additional maintenance. Woody plants can restrict or concentrate flows and can be damaged by erosion around the root ball and should not be placed directly in the bioretention entrance flow path. Bottom Area and Side Slopes Bioretention areas are highly adaptable and can fit various settings such as rural and urban roadsides, ultra urban streetscapes and parking lots by adjusting bottom area and side slope configuration. Recommended maximum and minimum dimensions include: Maximum planted side slope if total cell depth is greater than 3 feet: 3H:1V. If steeper side slopes are necessary rockeries, concrete walls or soil wraps may be effective design options. Local jurisdictions may require bike and/or pedestrian safety features, such as railings or curbs with curb cuts, when steep side slopes are adjacent to sidewalks, walkways, or bike lanes. Minimum bottom width for bioretention swales: 2 feet recommended and 1 foot minimum. Carefully consider flow depths and velocities, flow velocity control (check dams) and appropriate vegetation or rock mulch to prevent erosion and channelization at bottom widths less than 2 feet. 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…17/25 Bioretention areas should have a minimum shoulder of 12 inches (30.5 cm) between the road edge and beginning of the bioretention side slope where flush curbs are used. Compaction effort for the shoulder should 90 percent proctor. Ponding Area Ponding depth recommendations: Maximum ponding depth: 12 inches (30.5 cm). Surface pool drawdown time: 24 hours For design on projects subject to I-3.4.5 MR5: On-Site Stormwater Management, and choosing to use The List Approach of that requirement, the bioretention BMP shall have a horizontally projected surface area below the overflow which is at least 5% of the area draining to it. The ponding area provides surface storage for storm flows, particulate settling, and the first stages of pollutant treatment within the bioretention BMP. Pool depth and draw-down rate are recommended to provide surface storage, adequate infiltration capability, and soil moisture conditions that allow for a range of appropriate plant species. Soils must be allowed to dry out periodically in order to: restore hydraulic capacity to receive flows from subsequent storms; maintain infiltration rates; maintain adequate soil oxygen levels for healthy soil biota and vegetation; provide proper soil conditions for biodegradation and retention of pollutants. Maximum designed depth of ponding (before surface overflow to a pipe or ditch) must be considered in light of drawdown time. For bioretention areas with underdrains, elevating the drain to create a temporary saturated zone beneath the drain is advised to promote denitrification (conversion of nitrate to nitrogen gas) and prolong moist soil conditions for plant survival during dry periods (see the Underdrain (optional) section below for details). Surface Overflow Surface overflow can be provided by vertical stand pipes that are connected to underdrain systems, by horizontal drainage pipes or armored overflow channels installed at the designed maximum ponding elevations. Overflow can also be provided by a curb cut at the down-gradient end of the bioretention area to direct overflows back to the street. Overflow conveyance structures are necessary for all bioretention BMPs to safely convey flows that exceed the capacity of the BMP and to protect downstream natural resources and property. The minimum freeboard from the invert of the overflow stand pipe, horizontal drainage pipe or earthen channel should be 6 inches unless otherwise specified by the local jurisdiction’s design standards. Soil Depth The bioretention soil mix depth must be 18 inches to provide Runoff Treatment and good growing conditions for selected plants. Ecology does not recommend bioretention soil mix depths greater than 18 inches due to preliminary monitoring results indicating that phosphorus can leach from the bioretention soil mix. Filter Fabrics 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…18/25 Do not use filter fabrics between the subgrade and the bioretention soil mix. The gradation between existing soils and bioretention soil mix is not great enough to allow significant migration of fines into the bioretention soil mix. Additionally, filter fabrics may clog with downward migration of fines from the bioretention soil mix. Underdrain (optional) Where the underlying native soils have a measured initial Ksat between 0.3 and 0.6 inches per hour, bioretention BMPs without an underdrain, or with an elevated underdrain directed to a surface outlet, may be used to satisfy The List Approach of I-3.4.5 MR5: On-Site Stormwater Management. Underdrained bioretention BMPs must meet the following criteria if they are used to satisfy The List Approach of I-3.4.5 MR5: On-Site Stormwater Management: the invert of the underdrain must be elevated 6 inches above the bottom of the aggregate bedding layer. A larger distance between the underdrain and bottom of the bedding layer is desirable, but cannot be used to trigger infeasibility due to inadequate vertical separation to the seasonal high water table, bedrock, or other impermeable layer. the distance between the bottom of the bioretention soil mix and the crown of the underdrain pipe must be not less than 6 but not more than 12 inches; the aggregate bedding layer must run the full length and the full width of the bottom of the bioretention BMP; the BMP must not be underlain by a low permeability liner that prevents infiltration into the native soil. Figure V-5.13: Typical Bioretention w/Underdrain depicts a bioretention BMP with an elevated underdrain. Figure V-5.14: Typical Bioretention w/Liner (Not LID) depicts a bioretention BMP with an underdrain and a low permeability liner. The latter is not considered a low impact development BMP. It cannot be used to implement The List Approach of I-3.4.5 MR5: On-Site Stormwater Management. The volume above an underdrain pipe in a bioretention BMP provides pollutant filtering and minor detention. However, only the void volume of the aggregate below the underdrain invert and above the bottom of the bioretention BMP (subgrade) can be used in the continuous runoff model for dead storage volume that provides Flow Control benefit. Assume a 40% void volume for the Type 26 mineral aggregate specified below. Underdrain systems should only be installed when the bioretention BMP is: Located near sensitive infrastructure (e.g., unsealed basements) and potential for flooding is likely. Used for filtering storm flows from gas stations or other pollutant hotspots (requires impermeable liner). Located above native soils with infiltration rates that are not adequate to meet maximum pool and system dewater rates, or are below a minimum rate allowed by the local government. The underdrain can be connected to a downstream bioretention swale, to another bioretention cell as part of a connected treatment system, daylight to a dispersion area using an effective flow dispersion practice, or to a storm drain. 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…19/25 Underdrain Pipe Underdrains shall be slotted, thick-walled plastic pipe. The slot opening should be smaller than the smallest aggregate gradation for the gravel filter bed (see Underdrain Aggregate Filter and Bedding Layer below) to prevent migration of the material into the drain. This configuration allows for pressurized water cleaning and root cutting if necessary. Underdrain pipe recommendations: Minimum pipe diameter: 4 inches (pipe diameter will depend on hydraulic capacity required, 4 to 8 inches is common). Slotted subsurface drain PVC per ASTM D1785 SCH 40. Slots should be cut perpendicular to the long axis of the pipe and be 0.04 to 0.069 inches by 1 inch long and be spaced 0.25 inches apart (spaced longitudinally). Slots should be arranged in four rows spaced on 45-degree centers and cover ½ of the circumference of the pipe. See Underdrain Aggregate Filter and Bedding Layer (below) for aggregate gradation appropriate for this slot size. Underdrains should be sloped at a minimum of 0.5 percent unless otherwise specified by an engineer. Perforated PVC or flexible slotted HDPE pipe cannot be cleaned with pressurized water or root cutting equipment, are less durable and are not recommended. Wrapping the underdrain pipe in filter fabric increases chances of clogging and is not recommended. A 6-inch rigid non-perforated observation pipe or other maintenance access should be connected to the underdrain every 250 to 300 feet to provide a clean-out port, as well as an observation well to monitor dewatering rates. Underdrain Aggregate Filter and Bedding Layer Aggregate filter and bedding layers buffer the underdrain system from sediment input and clogging. When properly selected for the soil gradation, geosynthetic filter fabrics can provide adequate protection from the migration of fines. However, aggregate filter and bedding layers, with proper gradations, provide a larger surface area for protecting underdrains and are preferred. Table V-5.3: Mineral Aggregate Gradation for Underdrain Filter and Bedding Layer Sieve size Percent Passing ¾ inch 100 ¼ inch 30-60 US No. 8 20-50 US No. 50 3-12 US No. 200 0-1 Note: The above gradation is a Type 26 mineral aggregate as detailed for gravel backfill for drains in the City of Seattle Standard Specifications for Road, Bridge, and Municipal Construction (Seattle Public Utilities, 2014). 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…20/25 Place the underdrain pipe on a bed of the Type 26 aggregate with a minimum thickness of 6 inches and cover with Type 26 aggregate to provide a 1-foot minimum depth around the top and sides of the slotted pipe. See the Low Impact Development Technical Guidance Manual for Puget Sound (Hinman and Wulkan, 2012). Orifice and Other Flow Control sStructures The minimum orifice diameter should be 0.5 inches to minimize clogging and maintenance requirements. Check Dams and Weirs Check dams are necessary for reducing flow velocity and potential erosion, as well as increasing detention time and infiltration capability on sloped sites. Typical materials include concrete, wood, rock, compacted dense soil covered with vegetation, and vegetated hedge rows. Design depends on Flow Control goals, local regulations for structures within road right-of-ways and aesthetics. Optimum spacing is determined by Flow Control benefit (modeling) in relation to cost consideration. See the Low Impact Development Technical Guidance Manual for Puget Sound (Hinman and Wulkan, 2012) for displays of typical designs. UIC Discharge Stormwater that has passed through the bioretention soil mix may also discharge to a gravel-filled dug or drilled drain. Underground Injection Control (UIC) regulations are applicable and must be followed (Chapter 173-218 WAC). See I-4 UIC Program. Hydraulic Restriction Layers: Adjacent roads, foundations or other infrastructure may require that infiltration pathways are restricted to prevent excessive hydrologic loading. Two types of restricting layers can be incorporated into bioretention designs: Clay (bentonite) liners are low permeability liners. Where clay liners are used underdrain systems are necessary. See V-1.3.3 Low Permeability Liners for guidelines. Geomembrane liners completely block infiltration to subgrade soils and are used for ground water protection when bioretention BMPs are installed to filter storm flows from pollutant hotspots or on sidewalls of bioretention areas to restrict lateral flows to roadbeds or other sensitive infrastructure. Where geomembrane liners are used to line the entire BMP, underdrain systems are necessary. See V-1.3.3 Low Permeability Liners for guidelines. Plant Materials In general, the predominant plant material utilized in bioretention areas are species adapted to stresses associated with wet and dry conditions. Soil moisture conditions will vary within the facility from saturated (bottom of cell) to relatively dry (rim of cell). Accordingly, wetland plants may be used in the lower areas, if saturated soil conditions exist for appropriate periods, and drought-tolerant species planted on the perimeter of the facility or on mounded areas. See the Low Impact Development Technical Guidance Manual for Puget Sound (Hinman and 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…21/25 Wulkan, 2012) for additional guidance and recommended plant species. See also City of Seattle's ROW bioretention plant lists found in Seattle's GSI Manual, Appendix G, at the following web address: https://www.seattle.gov/util/cs/groups/public/@spu/@engineering/documents/webcontent/1_079167.pdf The side slopes for the bioretention facility (vertical or sloped) can affect the plant selection and must be considered. Additionally, trees can be planted along the side slopes or bottom of bioretention cells that are unlined. Mulch Layer You can design bioretention areas with or without a mulch layer. When used, mulch shall be: Medium compost in the bottom of the BMP (compost is less likely to float during cell inundation). Compost shall not include biosolids or manures. Shredded or chipped hardwood or softwood on side slopes above ponding elevation and rim area. Arborist mulch is mostly woody trimmings from trees and shrubs and is a good source of mulch material. Wood chip operations are a good source for mulch material that has more control of size distribution and consistency. Do not use shredded construction wood debris or any shredded wood to which preservatives have been added. Free of weed seeds, soil, roots and other material that is not bole or branch wood and bark. A maximum of 2 to 3 inches thick. Mulch shall not be: Grass clippings (decomposing grass clippings are a source of nitrogen and are not recommended for mulch in bioretention areas). Pure bark (bark is essentially sterile and inhibits plant establishment). In bioretention areas where higher flow velocities are anticipated, an aggregate mulch may be used to dissipate flow energy and protect underlying bioretention soil mix. Aggregate mulch varies in size and type, but 1 to 1 1/2 inch gravel (rounded) decorative rock is typical. Runoff Model Representation Note that if the project is using bioretention to only meet The List Approach within I-3.4.5 MR5: On-Site Stormwater Management, there is no need to model the bioretention in a continuous runoff model. Size the bioretention as described above in Ponding Area. The guidance below is to show compliance with the LID Performance Standard in I-3.4.5 MR5: On-Site Stormwater Management, or the standards in I-3.4.6 MR6: Runoff Treatment, I-3.4.7 MR7: Flow Control, and/or I- 3.4.8 MR8: Wetlands Protection. Continuous runoff modeling software include modeling elements for bioretention. 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…22/25 The equations used by the elements are intended to simulate the wetting and drying of soil as well as how the soils function once they are saturated. This group of LID elements uses the modified Green Ampt equation to compute the surface infiltration into the amended soil. The water then moves through the top amended soil layer at the computed rate, determined by Darcy’s and Van Genuchten’s equations. As the soil approaches field capacity (i.e., gravity head is greater than matric head), the model determines when water will begin to infiltrate into the second soil layer (lower layer). This occurs when the matric head is less than the gravity head in the first layer (top layer). The second layer is intended to prevent loss of the amended soil layer. As the second layer approaches field capacity, the water begins to move into the third layer – the gravel underlayer. For each layer, the user inputs the depth of the layer and the type of soil. Within the WWHM continuous runoff model, for the Ecology-recommended soil specifications for each layer in the design criteria for bioretention, the model will automatically assign pre-determined appropriate values for parameters that determine water movement through that soil. These include: wilting point, minimum hydraulic conductivity, maximum saturated hydraulic conductivity, and the Van Genuchten number. For bioretention with underlying perforated drain pipes that discharge to the surface, the only volume available for storage (and modeled as storage as explained herein) is the void space within the aggregate bedding layer below the invert of the drain pipe. Use 40% void space for the Type 26 mineral aggregate specified in Underdrain (optional) (above). Modeling: It is preferable to enter each bioretention device and its drainage area into the approved computer models for estimating their performance. However, where site layouts involve multiple bioretention facilities, the modeling schematic can become extremely complicated or not accommodated by the available schematic grid. In those cases, multiple bioretention facilities with similar designs (i.e., soil depth, ponding depth, freeboard height, and drainage area to ponding area ratio), and infiltration rates (Ecology suggests within a factor of 2) may have their drainage areas and ponded areas be combined, and represented in the runoff model as one drainage area and one bioretention device. In this case, use a weighted average of the design infiltration rates at each location. The averages are weighted by the size of their drainage areas. For bioretention with side slopes of 3H:1V or flatter, infiltration through the side slope areas can be significant. Where side slopes are 3H:1V or flatter, bioretention can be modeled allowing infiltration through the side slope areas to the native soil. In WWHM, modeling of infiltration through the side slope areas is accomplished by switching the default setting for “Use Wetted Surface Area (sidewalls): from “NO” to “YES.” Installation Criteria Excavation Soil compaction can lead to bioretention BMP failure; accordingly, minimizing compaction of the base and sidewalls of the bioretention area is critical. Excavation should never be allowed during wet or saturated conditions (compaction can reach depths of 2-3 feet during wet conditions and mitigation is likely to not be 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…23/25 possible). Excavation should be performed by machinery operating adjacent to the bioretention BMP, and no heavy equipment with narrow tracks, narrow tires, or large lugged, high pressure tires should be allowed on the bottom of the bioretention BMP. If machinery must operate in the bioretention area for excavation, use light weight, low ground-contact pressure equipment and rip the base at completion to refracture soil to a minimum of 12 inches. If machinery operates in the BMP footprint, subgrade infiltration rates must be field tested and compared to initial Ksat tests obtained during design. Failure to meet or exceed the initial Ksat tests will require revised engineering designs to verify achievement of Runoff Treatment and Flow Control benefits that were estimated in the Stormwater Site Plan. Prior to placement of the bioretention soil mix, the finished subgrade shall: Be scarified to a minimum depth of 3 inches. Have any sediment deposited from construction runoff removed. To remove all introduced sediment, subgrade soil should be removed to a depth of 3-6 inches and replaced with bioretention soil mix. Be inspected by the responsible engineer to verify required subgrade condition. Sidewalls of the BMP, beneath the surface of the bioretention soil mix, can be vertical if soil stability is adequate. Exposed sidewalls of the completed bioretention area with bioretention soil mix in place should be no steeper than 3H:1V. The bottom of the BMP should be flat. Soil Placement On-site soil mixing or placement shall not be performed if bioretention soil mix or subgrade soil is saturated. The bioretention soil mix should be placed and graded by machinery operating adjacent to the bioretention BMP. If machinery must operate in the bioretention cell for soil placement, use light weight equipment with low ground- contact pressure. If machinery operates in the BMP footprint, subgrade infiltration rates must be field tested and compared to initial Ksat tests obtained during design. Failure to meet or exceed the initial Ksat tests will require revised engineering designs to verify achievement of Runoff Treatment and Flow Control benefits that were estimated in the Stormwater Site Plan. The soil mixture shall be placed in horizontal layers not to exceed 6 inches per lift for the entire area of the bioretention BMP. Compact the bioretention soil mix to a relative compaction of 85 percent of modified maximum dry density (ASTM D 1557). Compaction can be achieved by boot packing (simply walking over all areas of each lift), and then apply 0.2 inches (0.5 cm) of water per 1 inch (2.5 cm) of bioretention soil mix depth. Water for settling should be applied by spraying or sprinkling. Temporary Erosion and Sediment Control (TESC) Controlling erosion and sediment are most difficult during clearing, grading, and construction; accordingly, minimizing site disturbance to the greatest extent practicable is the most effective sediment management. During construction: 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…24/25 Bioretention BMPs should not be used as sediment control BMPs, and all drainage should be directed away from bioretention BMPs after initial rough grading. Flow can be directed away from the BMP with temporary diversion swales or other approved protection. If introduction of construction runoff cannot be avoided see below for guidelines. Construction on bioretention BMPs should not begin until all contributing drainage areas are stabilized according to erosion and sediment control BMPs and to the satisfaction of the engineer. If the design includes curb and gutter, the curb cuts and inlets should be blocked until bioretention soil mix and mulch have been placed and planting completed (when possible), and dispersion pads are in place. Every effort during design, construction sequencing and construction should be made to prevent sediment from entering bioretention BMPs. However, bioretention areas are often distributed throughout the project area and can present unique challenges during construction. See the Low Impact Development Technical Guidance Manual for Puget Sound (Hinman and Wulkan, 2012) for guidelines if no other options exist and runoff during construction must be directed through the bioretention BMPs. Erosion and sediment control practices must be inspected and maintained on a regular basis. Verification If using the default bioretention soil mix, pre-placement laboratory analysis for saturated hydraulic conductivity of the bioretention soil mix is not required. Verification of the mineral aggregate gradation, compliance with the compost specifications, and the mix ratio must be provided. If using a custom bioretention soil mix, verification of compliance with the minimum design criteria cited above for such custom mixes must be provided. This will require laboratory testing of the material that will be used in the installation. Testing shall be performed by a Seal of Testing Assurance, AASHTO, ASTM or other standards organization accredited laboratory with current and maintained certification. Samples for testing must be supplied from the bioretention soil mix that will be placed in the bioretention areas. If testing infiltration rates is necessary for post-construction verification, use the Pilot Infiltration Test (PIT) method or a double ring infiltrometer test (or other small-scale testing allowed by the local government with jurisdiction). If using the PIT method, do not excavate the bioretention soil mix (conduct the test at the elevation of the finished bioretention soil mix), use a maximum of 6 inch ponding depth and conduct the test before plants are installed. Maintenance Bioretention areas require annual plant, soil, and mulch layer maintenance to ensure optimum infiltration, storage, and pollutant removal capabilities. In general, bioretention maintenance requirements are typical landscape care procedures and include: Watering: Plants should be selected to be drought tolerant and not require watering after establishment (2 to 3 years). Watering may be required during prolonged dry periods after plants are established. Erosion control: Inspect flow entrances, ponding area, and surface overflow areas periodically, and replace soil, plant material, and/or mulch layer in areas if erosion has occurred. Properly designed BMPs with 12/21/2020 BMP T7.30: Bioretention https://fortress.wa.gov/ecy/ezshare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc…25/25 appropriate flow velocities should not have erosion problems except perhaps in extreme events. If erosion problems occur, the following should be reassessed: (1) flow volumes from contributing areas and bioretention cell sizing; (2) flow velocities and gradients within the cell; and (3) flow dissipation and erosion protection strategies in the pretreatment area and flow entrance. If sediment is deposited in the bioretention area, immediately determine the source within the contributing area, stabilize, and remove excess surface deposits. Sediment removal: Follow the maintenance plan schedule for visual inspection and remove sediment if the volume of the ponding area has been compromised. Plant material: Depending on aesthetic requirements, occasional pruning and removing dead plant material may be necessary. Replace all dead plants and if specific plants have a high mortality rate, assess the cause and replace with appropriate species. Periodic weeding is necessary until plants are established. Weeding: Invasive or nuisance plants should be removed regularly and not allowed to accumulate and exclude planted species. At a minimum, schedule weeding with inspections to coincide with important horticultural cycles (e.g., prior to major weed varieties dispersing seeds). Weeding should be done manually and without herbicide applications. The weeding schedule should become less frequent if the appropriate plant species and planting density are used and the selected plants grow to capture the site and exclude undesirable weeds. Nutrient and pesticides: The soil mix and plants are selected for optimum fertility, plant establishment, and growth. Nutrient and pesticide inputs should not be required and may degrade the pollutant processing capability of the bioretention area, as well as contribute pollutant loads to receiving waters. By design, bioretention BMPs are located in areas where phosphorous and nitrogen levels may be elevated and these should not be limiting nutrients. If in question, have soil analyzed for fertility. Mulch: Replace mulch annually in bioretention BMPs where heavy metal deposition is high (e.g., contributing areas that include gas stations, ports and roads with high traffic loads). In residential settings or other areas where metals or other pollutant loads are not anticipated to be high, replace or add mulch as needed (likely 3 to 5 years) to maintain a 2 to 3 inch depth. Soil: Soil mixes for bioretention BMPs are designed to maintain long-term fertility and pollutant processing capability. Estimates from metal attenuation research suggest that metal accumulation should not present an environmental concern for at least 20 years in bioretention systems, but this will vary according to pollutant load. Replacing mulch media in bioretention BMPs where heavy metal deposition is likely provides an additional level of protection for prolonged performance. If in question, have soil analyzed for fertility and pollutant levels. Refer to Appendix V-A: BMP Maintenance Tables for additional maintenance guidelines. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 Edge of pavement or curb -cut 2" woodchip mulch or aggregate Provide a 1" drop from the edge of pavement Overflow structure or flow path Notes: 1. Scarify subgrade 3" min. before bioretention soil installation 2. Compact BSM to 85% per ASTM 1577 1100 q%W" DEPARTMENT OF ECOLOGY State of Washington Provide a 1" drop from the edge of sidewalk BSM bottom width varies, V minimum 6" min. freeboard Ponding depth I \ / Minimum separation varies, see design guidance Sidewalk III- —111-11 I- 2" woodchip mulch or aggregate 3" coarse compost in ponding area 18" Bioretention Soil Mix (BSM) Seasonal high water table, bedrock, or other impervious layer Typical Bioretention NOT TO SCALE Revised January 2019 Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. Edge of pavement or curb -cut 2" woodchip mulch or aggregate Provide a 1" drop from the edge of pavement Overflow structure or flow path 6" to 12" (see note 3) BSM bottom width varies, 1' minimum min. Ponding depth \Y,, varies Provide a 1" drop from the edge of sidewalk 1P 6" (see note 4) Mineral aggregate bottom width to match BSM bottom width Sidewalk 2" woodchip mulch or aggregate 3" coarse compost in ponding area 18" Bioretention Soil Mix (BSM) Mineral aggregate Underdrain pipe Notes: 1. Scarify subgrade 3" min. before BSM installation 2. Compact BSM to 85% per ASTM 1577 3. Minimum 6" to discourage fines from entering the underdrain from the BSM. Maximum 12" to prevent unnecessary BMP depth from encroaching into the seasonal high ground water. 4. If depth to the seasonal high ground water allows, this distance may be larger. 5. When an underdrain is used, the design must ensure that the seasonal high ground water does not encroach into the BMP (including the mineral aggregate layer surrounding the underdrain pipe). waa qlap" DEPARTMENT OF ECOLOGY State of Washington NOT TO SCALE Typical Bioretention w/Underdrain Revised January 2019 Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. Provide a 1" drop from the edge of pavement "curb-cut Overflow structure or flowpath 2" woodchip mulch or aggregate 6" to 12" Low permeability liner Notes: 1. Scarify subgrade 3" min. before bioretention soil installation 2. Compact BSM to 85% per ASTM 1577 1100 DEPARTMENT OF ECOLOGY State of Washington BSM bottom width varies, 1' minimum Ponding depth \vi varies Width varies Provide a 1" drop from the edge of sidewalk min. Sidewalk III 2" woodchip mulch or aggregate 3" coarse compost in ponding area 18" Bioretention Soil Mix (BSM) Mineral aggregate - Underdrain pipe NOT TO SCALE Typical Bioretention w/Liner (Not LID) Revised January 2019 Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. D EPARTMENT OF ECOLOGY State of Washington Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. Example of a Bioretention Planter Revised October 2016 NOT TO SCALE DESIGNER INFORMATION: 1. Adapt plan view example to yourengineered design.2. Include beginning and ending stations foreach facility. Provide stations and/ordimensions and elevations at every inlet,outlet, check dam, planter corner andsidewalk notch.3. Longitudinal slope of planter matches road.4. Sidewalk elevation must be set above inletand outlet elevations to allow overflow todrain to street before sidewalk.5. Minimum interior planter width is 3 feet. Aminimum of 4 feet interior planter width isrequired for street trees in planter.6. Existing utility lines must be sleeved orrelocated. Proposed utility lines to belocated out of the facility.7. Area and depth of facility are based uponengineering calculations and right-of-wayconstraints.8. May use concrete or pavers.OverflowStreetInflowMetal inletSpecify lengthCurb&gutter 2'-6"6"3'-0" min.6"Sidewalk Channel & grate (see note 2) 4" notch for sidewalk drianage, as necessary PlanterCheck dam (see note 2) 4" thick concrete splash pad at inlet 1'-6" Concrete or pavers 6'-0" typ. AA Plan View Section A-A 2'-6" Finished grade of planter Concrete or pavers (to be specified by designer) Curb and gutter (by others) Existing subgrade Open graded aggregate (when required) 3'-0" min 18" min Bioretention Soil Mix 6" bench for curb construction Planter wall Sidewalk drainage notch to be 1" lower than sidewalk, sloped to facility Top of wall at end of planter 12" max 4" min. exposed wall Attachment L Runoff Treatment BMPS 12/21/2020 BMP T7.30: Bioretention You are here: 2019 SWMMWW > Volume V - Runoff Treatment, Flow Control, and LID BMP Library_ > V-5 Infiltration BMPs > BMP T7.30: Bioretention BMP T7.30: Bioretention Purpose Ecology accepts bioretention as having the potential to meet 1-3.4.5 MRS: On -Site Stormwater Management, I- 3.4.6 MR6: Runoff Treatment and 1-3.4.7 MR7: Flow Control for the tributary drainage areas depending upon site conditions and sizing. The purpose of bioretention is to provide effective removal of many stormwater pollutants, and provide reductions in stormwater runoff quantity and surface runoff flow rates. Where the surrounding native soils have adequate infiltration rates, bioretention can provide both Runoff Treatment and Flow Control. Where the native soils have low infiltration rates, underdrain systems can be installed and the bioretention BMP can still be used as a Runoff Treatment BMP. However, designs utilizing underdrains provide less Flow Control benefits. Description Bioretention areas are shallow landscaped depressions, with a designed soil mix (the bioretention soil mix) and plants adapted to the local climate and soil moisture conditions, that receive stormwater from a contributing area. Bioretention uses the imported bioretention soil mix as a treatment medium. As in infiltration, the pollutant removal mechanisms include filtration, adsorption, and biological action. Bioretention BMPs can be built within earthen swales or placed within vaults. Water that has passed through the bioretention soil mix (or approved equivalent) may be discharged to the ground or collected and discharged to surface water. The term, bioretention, is used to describe various designs using soil and plant complexes to manage stormwater. The following terminology is used in this manual: • Bioretention cells: Shallow depressions with a designed planting soil mix and a variety of plant material, including trees, shrubs, grasses, and/or other herbaceous plants. Bioretention cells may or may not have an underdrain and are not designed as a conveyance system. • Bioretention swales: Incorporate the same design features as bioretention cells; however, bioretention swales are designed as part of a system that can convey stormwater when maximum ponding depth is exceeded. Bioretention swales have relatively gentle side slopes and ponding depths that are typically 6 to 12 inches. • Bioretention planters and planter boxes: Bioretention soil mix and a variety of plant material including trees, shrubs, grasses, and/or other herbaceous plants within a vertical walled container usually constructed from formed concrete, but could include other materials. Planter boxes are completely impervious and include a bottom (must include an underdrain). Planters have an open bottom and allow infiltration to the subgrade. These designs are often used in ultra -urban settings. https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/2019SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 1/25 12/21/2020 BMP T7.30: Bioretention Stormwater planters in the ROW require urban design and tailoring it to street typology and context. NACTO Urban Street Stormwater Guide provides guidance for designing roadside stormwater planters. httpa//nacto.org/publication/urban-street-stormwater-guide/ See Figure V-5.12: Typical Bioretention, Figure V-5.13: Typical Bioretention w/Underdrain, Figure V-5.14: Typical Bioretention w/Liner (Not LID), and Figure V-5.15: Example of a Bioretention Planter for examples of various types of bioretention configurations. Note: Ecology has approved use of certain manufactured treatment devices that use specific, high rate media for treatment. Such systems do not use bioretention soil mix, and are not considered a bioretention BMP (even though marketing materials for these manufactured treatment devices may compare them to bioretention). See V- 10 Manufactured Treatment Devices as BMPs for more information on manufactured treatment devices. pdf download pdf download pdf download pdf download Figure V-5.12: Typical Bioretention Figure V-5.13: Typical Bioretention w/Underdrain Figure V-5.14: Typical Bioretention w/Liner (Not LID) Figure V-5.15: Example of a Bioretention Planter https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 2/25 12/21/2020 BMP T7.30: Bioretention Applications and Limitations Because bioretention BMPs use an imported soil mix that has a moderate design infiltration rate, they are best applied for small drainages, and near the source of the stormwater runoff. Bioretention cells may be scattered throughout a subdivision; a bioretention swale may run alongside the access road; or a series of bioretention planter boxes may serve the road. In these situations, they can but are not required to fully meet the requirement to treat 91 % of the stormwater runoff file (the Water Quality Design Volume, as described in III -2.6 Sizing Your Runoff Treatment BMPs) from pollution -generating surfaces. The amount of stormwater that is predicted to pass through the bioretention soil mix is treated, and may be subtracted from the 91 % volume that must be treated to meet 1-3.4.6 MR6: Runoff Treatment. Downstream Runoff Treatment BMPs may be significantly smaller as a result. Bioretention BMPs that infiltrate into the ground can also provide significant Flow Control. They can, but are not required to fully meet the Flow Control Performance Standard of 1-3.4.7 MR7: Flow Control. Because they typically do not have an orifice restricting overflow or underflow discharge rates, they typically don't fully meet 1-3.4.7 MR7: Flow Control. However, their performance contributes to meeting the standard, and that can result in much smaller additional Flow Control BMPs at the bottom of the project site. Bioretention can also help achieve compliance with the LID Performance Standard of 1-3.4.5 MRS: On -Site Stormwater Management. Bioretention constructed with imported composted material should not be used within one-quarter mile of phosphorus -sensitive waterbodies if the underlying native soil does not meet the criteria for Runoff Treatment per V-5.6 Site Suitability Criteria (SSC). Preliminary monitoring indicates that new bioretention BMPs can add phosphorus to stormwater. Therefore, they should also not be used with an underdrain when the underdrain water would be routed to a phosphorus -sensitive receiving water. Applications with or without underdrains vary extensively and can be applied in new development, redevelopment and retrofits. Typical applications include: • Individual lots for rooftop, driveway, and other on -lot impervious surfaces. • Shared facilities located in common areas for individual lots. • Areas within loop roads or cul-de-sacs. • Landscaped parking lot islands. • Within right-of-ways along roads (often linear bioretention swales or cells). • Common landscaped areas in apartment complexes or other multifamily housing designs. • Planters on building roofs, patios, and as part of streetscapes. Infeasibility Criteria The following infeasibility criteria describe conditions that make bioretention infeasible when applying The List Approach within 1-3.4.5 MR5: On -Site Stormwater Management. If a project proponent wishes to use a https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 3/25 12/21/2020 BMP T7.30: Bioretention bioretention BMP even though one of the infeasibility criteria within this section are met„ they may propose a functional design to the local government. Criteria with setback distances are as measured from the bottom edge of the bioretention soil mix. Any of the following circumstances allow the designer to determine bioretention as "infeasible" when applying the The List Approach within 1-3.4.5 MRS: On -Site Stormwater Management: • Citation of any of the following infeasibility criteria must be based on an evaluation of site-specific conditions and a written recommendation from an appropriate licensed professional (e.g., engineer, geologist, hydrogeologist): o Where professional geotechnical evaluation recommends infiltration not be used due to reasonable concerns about erosion, slope failure, or down gradient flooding. o Within an area whose ground water drains into an erosion hazard, or landslide hazard area. o Where the only area available for siting would threaten the safety or reliability of pre-existing underground utilities, pre-existing underground storage tanks, pre-existing structures, or pre-existing road or parking lot surfaces. o Where the only area available for siting does not allow for a safe overflow pathway to the municipal separate storm sewer system or private storm sewer system. o Where there is a lack of usable space for bioretention BMPs at re -development sites, or where there is insufficient space within the existing public right-of-way on public road projects. o Where infiltrating water would threaten existing below grade basements. o Where infiltrating water would threaten shoreline structures such as bulkheads. • The following infeasibility criteria are based on conditions such as topography and distances to predetermined boundaries. Citation of the following criteria do not need site-specific written recommendations from a licensed professional, although some may require professional services to determine: o Within setbacks from structures as established by the local government with jurisdiction. o Where they are not compatible with the surrounding drainage system as determined by the local government with jurisdiction (e.g., project drains to an existing stormwater collection system whose elevation or location precludes connection to a properly functioning bioretention BMP) o Where land for bioretention is within area designated as an erosion hazard or landslide hazard. o Where the site cannot be reasonably designed to locate bioretention BMPs on slopes less than 8%. o Within 50 feet from the top of slopes that are greater than 20% and over 10 feet of vertical relief. o For properties with known soil or ground water contamination (typically federal Superfund sites or state cleanup sites under the Model Toxics Control Act (MTCA)): https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 4/25 12/21/2020 BMP T7.30: Bioretention ■ Within 100 feet of an area known to have deep soil contamination; ■ Where ground water modeling indicates infiltration will likely increase or change the direction of the migration of pollutants in the ground water; ■ Wherever surface soils have been found to be contaminated unless those soils are removed within 10 horizontal feet from the infiltration area; ■ Any area where these BMPs are prohibited by an approved cleanup plan under the state Model Toxics Control Act or Federal Superfund Law, or an environmental covenant under Chapter 64.70 RCW. o Within 100 feet of a closed or active landfill. o Within 100 feet of a drinking water well, or a spring used for drinking water supply. o Within 10 feet of small on-site sewage disposal drainfield, including reserve areas, and grey water reuse systems. For setbacks from a "large on-site sewage disposal system", see Chapter 246-272B WAC. o Within 10 feet of an underground storage tank and connecting underground pipes when the capacity of the tank and pipe system is 1100 gallons or less. (As used in these criteria, an underground storage tank means any tank used to store petroleum products, chemicals, or liquid hazardous wastes of which 10% or more of the storage volume (including volume in the connecting piping system) is beneath the ground surface. o Within 100 feet of an underground storage tank and connecting underground pipes when the capacity of the tank and pipe system is greater than 1100 gallons. o Where the minimum vertical separation of 1 foot to the seasonal high water table, bedrock, or other impervious layer would not be achieved below bioretention that would serve a drainage area that is less than: 1. 5,000 sq. ft. of pollution -generating impervious surface, and 2. 10,000 sq. ft. of impervious surface, and 3. three-quarter (3/4) acres of pervious surface. o Where the minimum vertical separation of 3 feet to the seasonal high water table, bedrock, or other impervious layer would not be achieved below bioretention that would serve a drainage area that meets or exceeds: AND 1. 5,000 sq. ft. of pollution -generating impervious surface, or 2. 10,000 sq. ft. of impervious surface, or 3. three-quarter (3/4) acres of pervious surface. https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 5/25 12/21/2020 BMP T7.30: Bioretention cannot reasonably be broken down into amounts smaller than those listed in 1-3 (above). o Where the field testing indicates potential bioretention sites have a measured (a.k.a., initial) native soil saturated hydraulic conductivity less than 0.30 inches per hour. If the measured native soil infiltration rate is less than 0.30 in/hour, bioretention should not be used to meet the The List Approach of I-3.4.5 MRS: On -Site Stormwater Management. In these slow draining soils, a bioretention BMP with an underdrain may be used to treat pollution -generating surfaces to help meet I-3.4.6 MR6: Runoff Treatment. If the underdrain is elevated within a base course of gravel, the bioretention BMP will also provide some modest flow reduction benefit that will help achieve the LID Performance Standard within 1-3.4.5 MR5: On -Site Stormwater Management and/or the Flow Control Performance Standard within 1-3.4.7 MR7: Flow Control. • A local government may designate geographic boundaries within which bioretention BMPs may be designated as infeasible due to year-round, seasonal or periodic high groundwater conditions, or due to inadequate infiltration rates. Designations must be based upon a pre-ponderance of field data, collected within the area of concern, that indicate a high likelihood of failure to achieve the minimum ground water clearance or infiltration rates identified in the above infeasibility criteria. The local government must develop a technical report and make it available upon request to Ecology. The report must be authored by (a) professional(s) with appropriate expertise (e.g., registered engineer, geologist, hydrogeologist, or certified soil scientist), and document the location and the pertinent values/observations of data that were used to recommend the designation and boundaries for the geographic area. The types of pertinent data include, but are not limited to: o Standing water heights or evidence of recent saturated conditions in observation wells, test pits, test holes, and well logs. o Observations of areal extent and time of surface ponding, including local government or professional observations of high water tables, frequent or long durations of standing water, springs, wetlands, and/or frequent flooding. o Results of infiltration tests • In addition, a local government can map areas that meet a specific infeasibility criterion listed above provided they have an adequate data basis. Criteria that are most amenable to mapping are: o Where land for bioretention is within an area designated by the local government as an erosion hazard, or landslide hazard o Within 50 feet from the top of slopes that are greater than 20% and over 10 feet vertical relief o Within 100 feet of a closed or active landfill Design Criteria General Design Criteria https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 6/25 12/21/2020 BMP T7.30: Bioretention • Utility conflicts: Consult local jurisdiction requirements for horizontal and vertical separation required for publicly -owned utilities, such as water and sewer. Consult the appropriate franchise utility owners for separation requirements from their utilities, which may include communications and gas. When separation requirements cannot be met, designs should include appropriate mitigation measures, such as impermeable liners over the utility, sleeving utilities, fixing known leaky joints or cracked conduits, and/or adding an underdrain to the bioretention. • Transportation safety: The design configuration and selected plant types should provide adequate sight distances, clear zones, and appropriate setbacks for roadway applications in accordance with local jurisdiction requirements. • Ponding depth and surface water draw -down: Flow Control needs, as well as location in the development, and mosquito breeding cycles will determine draw -down timing. For example, front yards and entrances to residential or commercial developments may require rapid surface dewatering for aesthetics. In no case shall draw down time exceed 48 hours. • Impacts of surrounding activities: Human activity influences the location of the BMP in the development. For example, locate bioretention BMPs away from traveled areas on individual lots to prevent soil compaction and damage to vegetation or provide elevated or bermed pathways in areas where foot traffic is inevitable. Provide barriers, such as wheel stops, to restrict vehicle access in roadside applications. • Visual buffering: Bioretention BMPs can be used to buffer structures from roads, enhance privacy among residences, and for an aesthetic site feature. • Site growing characteristics and plant selection: Appropriate plants should be selected for sun exposure, soil moisture, and adjacent plant communities. Native species or hardy cultivars are recommended and can flourish in the properly designed and placed bioretention soil mix with no nutrient or pesticide inputs and 2-3 years irrigation for establishment. Invasive species and noxious weed control will be required as typical with all planted landscape areas. • Project submission requirements: Submit the results of infiltration (Ksat) testing and ground water elevation testing (or other documentation and justification for the rates and hydraulic restriction layer clearances) with the Stormwater Site Plan as justification for the feasibility decision regarding bioretention and as justification for assumptions made in the runoff modeling. • Legal documentation to track bioretention obligations: Where drainage plan submittals include assumptions with regard to size and location of bioretention BMPs, approval of the plat, short -plat, or building permit should identify the bioretention obligation of each lot; and the appropriate lots should have deed requirements for construction and maintenance of those BMPs • Much of the design criteria within this BMP originated from the Low Impact Development Technical Guidance Manual for Puget Sound .(Hinman and Wulkan, 2012). Refer to that document for additional explanations and background. Note that the Low Impact Development Technical Guidance Manual for Puget Sound .(Hinman and Wulkan, 2012) is for additional information purposes only. You must follow the guidance within this manual if there https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWMMWW/2019SWMMWW.htm#Topics/VolumeV/infiltrationBMPs/BMPt730.htm%3FToc... 7/25 12/21/2020 BMP T7.30: Bioretention are any discrepancies between this manual and the Low Impact Development Technical Guidance Manual for Puget Sound .(Hinman and Wulkan, 2012). • Geotechnical analysis is an important first step to develop an initial assessment of the variability of site soils, infiltration characteristics and the necessary frequency and depth of infiltration tests. See V-5.2 Infiltration BMP Design Steps. Determining the Native Soil Infiltration Rates Determining infiltration rates of the site soils is necessary to determine feasibility of designs that intend to infiltrate stormwater on-site. It is also necessary to estimate flow reduction benefits of such designs when using a continuous runoff model. The certified soils professional or engineer can exercise discretion concerning the need for and extent of infiltration rate (saturated hydraulic conductivity, Ksat) testing. The professional can consider a reduction in the extent of infiltration (Ksat) testing if, in their judgment, information exists confirming that the site is unconsolidated outwash material with high infiltration rates, and there is adequate separation from ground water. The following provides recommended tests for the soils underlying bioretention BMPs. The test should be run at the anticipated elevation of the top of the native soil beneath the bioretention BMP. Refer to V-5.4 Determining the Design Infiltration Rate of the Native Soils for further guidance on the methods to determine the infiltration rate of the native soils. • Small bioretention cells (bioretention BMPs made up of one or multiple cells that receive water from 1 or 2 individual lots or < 1/4 acre of pavement or other impervious surface) have the following options for determining the native soil infiltration rate: 1. Small-scale pilot infiltration test (PIT) as described in V-5.4 Determining the Design Infiltration Rate of the Native Soils. 2. If the site is underlain with soils not consolidated by glacial advance (e.g., recessional outwash soils), then the designer may use the grain size analysis method described in V-5.4 Determining the Design Infiltration Rate of the Native Soils based on the layer(s) identified in results of one soil test pit or boring. • Large bioretention cells (bioretention BMPs made up of one or multiple cells that receive water from several lots or 1/4 acre or more of pavement or other impervious surface) have the following options for determining the native soil infiltration rate: 1. Multiple small-scale or one large-scale PIT. If using the small-scale test, measurements should be taken at several locations within the area of interest. 2. If the site is underlain with soils not consolidated by glacial advance (e.g., recessional outwash soils), then the designer may use the grain size analysis method described in V-5.4 Determining the Design Infiltration Rate of the Native Soils. Use the grain size analysis method based on more than one soil test pit or boring. The more test pits/borings used, and the more evidence of consistency in the soils, the less of a correction factor may be used. https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWMMWW/2019SWMMWW.htm#Topics/VolumeV/infiltrationBMPs/BMPt730.htm%3FToc... 8/25 12/21/2020 BMP T7.30: Bioretention • Bioretention swales have the following options for determining the native soil infiltration rate: 1. Approximately 1 small-scale PIT per 200 feet of swale, and within each length of road with significant differences in subsurface characteristics. 2. If the site is underlain with soils not consolidated by glacial advance (e.g., recessional outwash soils), then the designer may use the grain size analysis method described in V-5.4 Determining the Design Infiltration Rate of the Native Soils. Approximately 1 soil test pit/boring per 200 feet of swale and within each length of road with significant differences in subsurface characteristics. • On a single, smaller commercial property, one bioretention BMP will likely be appropriate. In that case, a small-scale PIT — or an alternative small scale test specified by the local government - should be performed at the proposed bioretention location. Tests at more than one site could reveal the advantages of one location over another. On larger commercial sites, a small-scale PIT every 5,000 sq. ft. is advisable. If soil characteristics across the site are consistent, a geotechnical professional may recommend a reduction in the number of tests. • On multi -lot residential developments, multiple bioretention BMPs, or a BMP stretching over multiple properties are appropriate. In most cases, it is necessary to perform small-scale PITs, or other small-scale tests as allowed by the local jurisdiction. A test is advisable at each potential bioretention site. Long, narrow bioretention BMPs, such as one following the road right-of-way, should have a test location at least every 200 lineal feet, and within each length of road with significant differences in subsurface characteristics. If the site subsurface characterization, including soil borings across the development site, indicate consistent soil characteristics and depths to seasonal high ground water conditions or a hydraulic restriction layer, the number of test locations may be reduced to a frequency recommended by a geotechnical professional. After concluding an infiltration test, infiltration test sites should be over -excavated 3 feet below the projected bioretention BMP's bottom elevation unless minimum clearances to seasonal high ground water have or will be determined by another method. This overexcavation is to determine if there are restrictive layers or ground water. Observe whether water is infiltrating vertically or only spreading horizontally because of ground water or a restrictive soil layer. Observations through a wet season can identify a seasonal ground water restriction. If a single bioretention BMP serves a drainage area exceeding 1 acre, a ground water mounding analysis may be necessary in accordance with V-5.2 Infiltration BMP Design Steps. Assignment of Appropriate Correction Factors to the Native Soil If the design requires determination of a long-term (design) infiltration rate of the native soils (for example, to demonstrate compliance with the LID Performance Standard and/or the Flow Control Performance Standard), refer to V-5.4 Determining the Design Infiltration Rate of the Native Soils and the following additional guidance specific to bioretention BMPs: • The overlying bioretention soil mix provides excellent protection for the underlying native soil from sedimentation. Accordingly, when using The Simplified Approach to Calculating the Design Infiltration Rate of the Native Soils as described in V-5.4 Determining the Design Infiltration Rate of the Native Soils, the https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/2019SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 9/25 12/21/2020 BMP T7.30: Bioretention correction factor for the sub -grade soil does not have to take into consideration the extent of influent control and clogging over time. The correction factor to be applied to in-situ, small-scale infiltration test results for bioretention sites is determined by the site variability and number of locations tested as well as the method used to determine initial Ksat• Using Table V-5.1: Correction Factors to be Used With In -Situ Saturated Hydraulic Conductivity Measurements to Estimate Design Rates, the correction factor for bioretention design is revised based on this guidance as: Total Correction Factor, CFT = CFV x CFt • Tests should be located and be at an adequate frequency capable of producing a soil profile characterization that fully represents the infiltration capability where the bioretention areas are to be located. The partial correction factor CFV depends on the level of uncertainty that variable subsurface conditions justify. If a pilot infiltration test is conducted for all bioretention areas or the range of uncertainty is low (for example, conditions are known to be uniform through previous exploration and site geological factors) one pilot infiltration test may be adequate to justify a CFV of one. If the level of uncertainty is high, a CFV near the low end of the range may be appropriate. Two example scenarios where low CFVs may be appropriate include: o Site conditions are highly variable due to a deposit of ancient landslide debris, or buried stream channels. In these cases, even with many explorations and several pilot infiltration tests, the level of uncertainty may still be high. o Conditions are variable, but few explorations and only one pilot infiltration test is conducted. That is, the number of explorations and tests conducted do not match the degree of site variability anticipated. Determining the Bioretention Soil Mix Design Infiltration Rate 1. Determine the initial saturated hydraulic conductivity (Ksat) based on the type of bioretention soil mix, as follows: o If using Ecology's default bioretention soil mix (detailed below), the initial Ksat is 12 inches per hour (30.48 cm/hr). o If using a custom bioretention soil mix (per the guidance for custom mixes below), use ASTM D 2434 Standard Test Method for Permeability of Granular Soils (Constant Head) with a compaction rate of 85 percent using ASTM D1557 Test Method for Laboratory Compaction Characteristics of Soil Using Modified Effort. See the additional guidance below for specific procedures for conducting ASTM D 2434. The designer must enter the derived Ksat value into the continuous modeling software. 2. After determining the initial Ksat, determine the appropriate safety factor: o If the contributing area to the bioretention BMP is equal to or exceeds any of the following limitations: https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 10/25 12/21/2020 BMP T7.30: Bioretention o 5,000 square feet of pollution -generating impervious surface; o 10,000 square feet of impervious surface; o % acre of lawn and landscape, use 4 as the Ksat safety factor. o If the contributing area is less than all of the above areas, or if the design includes a pretreatment BMP for solids removal, use 2 as the Ksat safety factor. 3. The continuous runoff model has a field for entering Ksat and the appropriate safety factor. Recommended Modifications to ASTM D 2434 When Measuring Hydraulic Conductivity for Bioretention Soil Mixes Proctor method ASTM D1557 Method C (6 -inch mold) shall be used to determine maximum dry density values for compaction of the bioretention soil sample. Sample preparation for the Proctor test shall be amended in the following ways: 1. Maximum grain size within the sample shall be no more than '/2 inches in size. 2. Snip larger organic particles (if present) intol/2 inch long pieces. 3. When adding water to the sample during the Proctor test, allow the sample to pre-soak for at least 48 hours to allow the organics to fully saturate before compacting the sample. This pre-soak ensures the organics have been fully saturated at the time of the test. ASTM D2434 shall be used and amended in the following ways: 1. Apparatus: 2. Sample: a. 6 -inch mold size shall be used for the test. b. If using porous stone disks for the testing, the permeability of the stone disk shall be measured before and after the soil tests to ensure clogging or decreased permeability has not occurred during testing. c. Use the confined testing method, with 5- to 10 -pound force spring d. Use de -aired water. a. Maximum grain size within the sample shall not be more than '/2 inch in size. b. Snip larger organic particles (if present) into'/z-inch long pieces. c. Pre-soak the sample for at least 48 hours prior to loading it into the mold. During the pre- soak, the moisture content shall be higher than optimum moisture but less than full https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 11/25 12/21/2020 BMP T7.30: Bioretention saturation (i.e., there shall be no free water). This pre-soak ensures the organics have been fully saturated at the time of the test. 3. Preparation of Sample: a. Place soil in cylinder via a scoop. b. Place soil in 1 -inch lifts and compact using a 2 -inch -diameter round tamper. Pre -weigh how much soil is necessary to fill 1 -inch lift at 85% of maximum dry density, then tamp to 1 -inch thickness. Once mold is full, verify that density is at 85% of maximum dry density (+ or — 0.5%). Apply vacuum (20 inches Hg) for 15 minutes before inundation. c. Inundate sample slowly under a vacuum of 20 inches Hg over a period of 60 to 75 minutes. d. Slowly remove vacuum ( > 15 seconds). e. Sample shall be soaked in the mold for 24 to 72 hours before starting test. 4. Procedure: a. The permeability test shall be conducted over a range of hydraulic gradients between 0.1 and 2. b. Steady state flow rates shall be documented for four consecutive measurements before increasing the head. c. The permeability test shall be completed within one day (one -day test duration). Default Bioretention Soil Mix (BSM) Projects which use the following requirements for the bioretention soil mix do not have to test the mix for its saturated hydraulic conductivity (Ksat). See Determining the Bioretention Soil Mix Design Infiltration Rate. Mineral Aggregate for Default BSM Percent Fines: A range of 2 to 4 percent passing the #200 sieve is ideal and fines should not be above 5 percent for a proper functioning specification according to ASTM D422. Aggregate Gradation for Default BSM The aggregate portion of the BSM should be well -graded. According to ASTM D 2487-98 (Classification of Soils for Engineering Purposes (Unified Soil Classification System)), well -graded sand should have the following gradation coefficients: • Coefficient of Uniformity (Cu = D60/D10) equal to or greater than 4, and • Coefficient of Curve (Cc = (D30)2/D60 x D10) greater than or equal to 1 and less than or equal to 3. https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 12/25 12/21/2020 BMP T7.30: Bioretention Table V-5.2: General Guideline for Mineral Aggregate Gradation provides a gradation guideline for the aggregate component of the default bioretention soil mix .(Hinman, 2009). The sand gradation below is often supplied as a well -graded utility or screened. With compost this blend provides enough fines for adequate water retention, hydraulic conductivity within recommended range (see below), pollutant removal capability, and plant growth characteristics for meeting design guidelines and objectives. Table V-5.2: General Guideline for Mineral Aggregate Gradation Sieve Size Percent Passing 3/8" 100 #4 95-100 #10 75-90 #40 25-40 #100 4-10 #200 2-5 Where existing soils meet the above aggregate gradation, those soils may be amended rather than importing mineral aggregate. Compost to Aggregate Ratio, Organic Matter Content, and Cation Exchange Capacity for Default BSM • Compost to aggregate ratio: 60-65 percent mineral aggregate, 35 — 40 percent compost by volume. • Organic matter content: 5 — 8 percent by weight. • Cation Exchange Capacity (CEC) must be > 5 milliequivalents/100 g dry soil Note: Soil mixes meeting the above specifications do not have to be tested for CEC. They will readily meet the minimum CEC. Compost for Default BSM To ensure that the BSM will support healthy plant growth and root development, contribute to biofiltration of pollutants, and not restrict infiltration when used in the proportions cited herein, the following compost standards are required. • Meets the definition of "composted material" in WAC 173-350-100 and complies with testing parameters and other standards in WAC 173-350-220. • Produced at a composting facility that is permitted by the jurisdictional health authority. Permitted compost facilities in Washington are included in a spreadsheet titled Washington composting facilities and material types — 2017 at the following web address: https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc... 13/25 12/21/2020 BMP T7.30: Bioretention httpa//ecology.wa.gov/Waste-Toxics/Reducing-recycling-waste/Organic-materials/Managing-organics- compost • The compost product must originate a minimum of 65 percent by volume from recycled plant waste comprised of "yard debris," "crop residues," and "bulking agents" as those terms are defined in WAC 173- 350-100. A maximum of 35 percent by volume of "post -consumer food waste" as defined in WAC 173-350- 100, but not including biosolids or manure, may be substituted for recycled plant waste. • Stable (low oxygen use and CO2 generation) and mature (capable of supporting plant growth) by tests shown below. This is critical to plant success in bioretention soil mixes. • Moisture content range: no visible free water or dust produced when handling the material. • Tested in accordance with the U.S. Composting Council "Test Method for the Examination of Compost and Composting" (TMECC), as established in the Composting Council's "Seal of Testing Assurance" (STA) program. Most Washington compost facilities now use these tests. • Screened to the following size gradations for Fine Compost when tested in accordance with TMECC test method 02.02-B, Sample Sieving for Aggregate Size Classification." Fine Compost shall meet the following gradation by dry weight Minimum percent passing 2": 100% Minimum percent passing 1": 99% Minimum percent passing 5/8": 90% Minimum percent passing 1/4": 75% • pH between 6.0 and 8.5 (TMECC 04.11-A). "Physical contaminants" (as defined in WAC 173-350-100) content less that 1 % by weight (TMECC 03.08-A) total, not to exceed 0.25 percent film plastic by dry weight. • Minimum organic matter content of 40% (TMECC 05.07-A "Loss on Ignition) • Soluble salt content less than 4.0 dS/m (mmhos/cm) (TMECC 04.10-A "Electrical Conductivity, 1:5 Slurry Method, Mass Basis") • Maturity indicators from a cucumber bioassay (TMECC 05.05-A "Seedling Emergence and Relative Growth ) must be greater than 80%for both emergence and vigor") • Stability of 7 mg CO2-C/g OM/day or below (TMECC 05.08-B "Carbon Dioxide Evolution Rate") • Carbon to nitrogen ratio (TMECC 05.02A "Carbon to Nitrogen Ratio" which uses 04.01 "Organic Carbon" and 04.02D "Total Nitrogen by Oxidation") of less than 25:1. The C:N ratio may be up to 35:1 for plantings composed entirely of Puget Sound Lowland native species and up to 40:1 for coarse compost to be used as a surface mulch (not in a soil mix). Custom Bioretention Soil Mix https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWMMWW/2019SWMMWW.htm#Topics/VolumeV/infiltrationBMPs/BMPt730.htm%3FToc... 14/25 12/21/2020 BMP T7.30: Bioretention Projects which prefer to create a custom bioretention soil mix rather than using the default bioretention soil mix described above must demonstrate compliance with the following criteria using the specified test method: • CEC >_ 5 meq/100 grams of dry soil; USEPA 9081 • pH between 5.5 and 7.0 • 5 - 8 percent organic matter content before and after the saturated hydraulic conductivity test; ASTM D2974 (Standard Test Method for Moisture, Ash, and Organic Matter of Peat and Other Organic Soils) • 2-5 percent fines passing the 200 sieve; TMECC 04.11-A • Measured (Initial) saturated hydraulic conductivity (Ksat) of less than 12 inches per hour; ASTM D 2434 (Standard Test Method for Permeability of Granular Soils (Constant Head)) at 85% compaction per ASTM D 1557 (Standard Test Method s for Laboratory Compaction Characteristics of Soil Using Modified Effort). Also, use Recommended Modifications to ASTM D 2434 When Measuring Hydraulic Conductivity for Bioretention Soil Mixes (as detailed above). • Design (long-term) saturated hydraulic conductivity of more than 1 inch per hour. Note: Design saturated hydraulic conductivity is determined by applying the appropriate infiltration correction factors as explained above under Determining the Bioretention Soil Mix Design Infiltration Rate. • If compost is used in creating the custom bioretention soil mix, it must meet all of the specifications listed above in Compost for Default BSM, except for the gradation specification. An alternative gradation specification must indicate the minimum percent passing for a range of similar particle sizes. Flow Entrance and Presettling Flow entrance design will depend on topography, flow velocities and volume entering the pretreatment and bioretention area, adjacent land use and site constraints. Flow velocities entering bioretention should be less than 1.0 ft/second to minimize erosion potential. Flow entrances should be placed with adequate separation from outlets to ensure that the influent stormwater is treated prior to reaching the overflow. Five primary types of flow entrances can be used for bioretention: • Dispersed, low velocity flow across a landscape area: Landscape areas and vegetated buffer strips slow incoming flows and provide an initial settling of particulates and are the preferred method of delivering flows to bioretention. Dispersed flow may not be possible given space limitations or if the BMP is controlling roadway or parking lot flows where curbs are mandatory. • Dispersed or sheet flow across pavement or gravel and past wheel stops for parking areas. • Curb cuts for roadside, driveway or parking lot areas: Curb cuts should include a rock pad, concrete or other erosion protection material in the channel entrance to dissipate energy. Minimum curb cut width should be 12 inches; however, 18 inches is recommended. The designer should calculate the size and choose the style of curb cut that is appropriate for the site conditions and runoff expectations. Avoid the use of angular rock or quarry spalls and instead use round (river) rock if needed. Removing sediment from angular rock is difficult. The flow entrance should slope steeply (at least 1:1) from the curb line to the bioretention, dropping https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 15/25 12/21/2020 BMP T7.30: Bioretention at least 3", and provide an area for settling and periodic removal of sediment and coarse material before flow dissipates to the remainder of the bioretention area. Curb cuts used for bioretention areas in high use parking lots or roadways require an increased level of maintenance due to high coarse particulates and trash accumulation in the flow entrance and associated bypass of flows. The following are methods recommended for areas where heavy trash and coarse particulates are anticipated: o Curb cut width: 18 inches. o At a minimum the flow entrance should drop 2 to 3 inches from the gutter line into the bioretention area and provide an area for settling and periodic removal of debris. o Anticipate relatively more frequent inspection and maintenance for areas with large impervious areas, high traffic loads and larger debris loads. o Catch basins or forebays may be necessary at the flow entrance to adequately capture debris and sediment load from large contributing areas and high use areas. Piped flow entrance in this setting can easily clog and catch basins with regular maintenance are necessary to capture coarse and fine debris and sediment. • Pipe flow entrance: Piped entrances should include rock or other erosion protection material in the channel entrance to dissipate energy and disperse flow. • Catch basin: In some locations where road sanding or higher than usual sediment inputs are anticipated, catch basins can be used to settle sediment and release water to the bioretention area through a grate for filtering coarse material. • Trench drains: Trench drains can be used to cross sidewalks or driveways where a deeper pipe conveyance creates elevation problems. Trench drains tend to clog and may require additional maintenance. Woody plants can restrict or concentrate flows and can be damaged by erosion around the root ball and should not be placed directly in the bioretention entrance flow path. Bottom Area and Side Slopes Bioretention areas are highly adaptable and can fit various settings such as rural and urban roadsides, ultra urban streetscapes and parking lots by adjusting bottom area and side slope configuration. Recommended maximum and minimum dimensions include: • Maximum planted side slope if total cell depth is greater than 3 feet: 3H:1 V. If steeper side slopes are necessary rockeries, concrete walls or soil wraps may be effective design options. Local jurisdictions may require bike and/or pedestrian safety features, such as railings or curbs with curb cuts, when steep side slopes are adjacent to sidewalks, walkways, or bike lanes. • Minimum bottom width for bioretention swales: 2 feet recommended and 1 foot minimum. Carefully consider flow depths and velocities, flow velocity control (check dams) and appropriate vegetation or rock mulch to prevent erosion and channelization at bottom widths less than 2 feet. https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/2019SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 16/25 12/21/2020 BMP T7.30: Bioretention • Bioretention areas should have a minimum shoulder of 12 inches (30.5 cm) between the road edge and beginning of the bioretention side slope where flush curbs are used. Compaction effort for the shoulder should 90 percent proctor. Ponding Area Ponding depth recommendations: • Maximum ponding depth: 12 inches (30.5 cm). • Surface pool drawdown time: 24 hours For design on projects subject to 1-3.4.5 MRS: On -Site Stormwater Management, and choosing to use The List Approach of that requirement, the bioretention BMP shall have a horizontally projected surface area below the overflow which is at least 5% of the area draining to it. The ponding area provides surface storage for storm flows, particulate settling, and the first stages of pollutant treatment within the bioretention BMP. Pool depth and draw -down rate are recommended to provide surface storage, adequate infiltration capability, and soil moisture conditions that allow for a range of appropriate plant species. Soils must be allowed to dry out periodically in order to: restore hydraulic capacity to receive flows from subsequent storms; maintain infiltration rates; maintain adequate soil oxygen levels for healthy soil biota and vegetation; provide proper soil conditions for biodegradation and retention of pollutants. Maximum designed depth of ponding (before surface overflow to a pipe or ditch) must be considered in light of drawdown time. For bioretention areas with underdrains, elevating the drain to create a temporary saturated zone beneath the drain is advised to promote denitrification (conversion of nitrate to nitrogen gas) and prolong moist soil conditions for plant survival during dry periods (see the Underdrain (optional) section below for details). Surface Overflow Surface overflow can be provided by vertical stand pipes that are connected to underdrain systems, by horizontal drainage pipes or armored overflow channels installed at the designed maximum ponding elevations. Overflow can also be provided by a curb cut at the down -gradient end of the bioretention area to direct overflows back to the street. Overflow conveyance structures are necessary for all bioretention BMPs to safely convey flows that exceed the capacity of the BMP and to protect downstream natural resources and property. The minimum freeboard from the invert of the overflow stand pipe, horizontal drainage pipe or earthen channel should be 6 inches unless otherwise specified by the local jurisdiction's design standards. Soil Depth The bioretention soil mix depth must be 18 inches to provide Runoff Treatment and good growing conditions for selected plants. Ecology does not recommend bioretention soil mix depths greater than 18 inches due to preliminary monitoring results indicating that phosphorus can leach from the bioretention soil mix. Filter Fabrics https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 17/25 12/21/2020 BMP T7.30: Bioretention Do not use filter fabrics between the subgrade and the bioretention soil mix. The gradation between existing soils and bioretention soil mix is not great enough to allow significant migration of fines into the bioretention soil mix. Additionally, filter fabrics may clog with downward migration of fines from the bioretention soil mix. Underdrain (optional). Where the underlying native soils have a measured initial Ksat between 0.3 and 0.6 inches per hour, bioretention BMPs without an underdrain, or with an elevated underdrain directed to a surface outlet, may be used to satisfy The List Approach of 1-3.4.5 MR5: On -Site Stormwater Management. Underdrained bioretention BMPs must meet the following criteria if they are used to satisfy The List Approach of 1-3.4.5 MR5: On -Site Stormwater Management: • the invert of the underdrain must be elevated 6 inches above the bottom of the aggregate bedding layer. A larger distance between the underdrain and bottom of the bedding layer is desirable, but cannot be used to trigger infeasibility due to inadequate vertical separation to the seasonal high water table, bedrock, or other impermeable layer. • the distance between the bottom of the bioretention soil mix and the crown of the underdrain pipe must be not less than 6 but not more than 12 inches; • the aggregate bedding layer must run the full length and the full width of the bottom of the bioretention BMP; • the BMP must not be underlain by a low permeability liner that prevents infiltration into the native soil. Figure V-5.13: Typical Bioretention w/Underdrain depicts a bioretention BMP with an elevated underdrain. Figure V-5.14: Typical Bioretention w/Liner (Not LID) depicts a bioretention BMP with an underdrain and a low permeability liner. The latter is not considered a low impact development BMP. It cannot be used to implement The List Approach of I-3.4.5 MR5: On -Site Stormwater Management. The volume above an underdrain pipe in a bioretention BMP provides pollutant filtering and minor detention. However, only the void volume of the aggregate below the underdrain invert and above the bottom of the bioretention BMP (subgrade) can be used in the continuous runoff model for dead storage volume that provides Flow Control benefit. Assume a 40% void volume for the Type 26 mineral aggregate specified below. Underdrain systems should only be installed when the bioretention BMP is: • Located near sensitive infrastructure (e.g., unsealed basements) and potential for flooding is likely. • Used for filtering storm flows from gas stations or other pollutant hotspots (requires impermeable liner). • Located above native soils with infiltration rates that are not adequate to meet maximum pool and system dewater rates, or are below a minimum rate allowed by the local government. The underdrain can be connected to a downstream bioretention swale, to another bioretention cell as part of a connected treatment system, daylight to a dispersion area using an effective flow dispersion practice, or to a storm drain. https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 18/25 12/21/2020 Underdrain Pipe BMP T7.30: Bioretention Underdrains shall be slotted, thick-walled plastic pipe. The slot opening should be smaller than the smallest aggregate gradation for the gravel filter bed (see Underdrain Aggregate Filter and Bedding Layer below) to prevent migration of the material into the drain. This configuration allows for pressurized water cleaning and root cutting if necessary. Underdrain pipe recommendations: • Minimum pipe diameter: 4 inches (pipe diameter will depend on hydraulic capacity required, 4 to 8 inches is common). • Slotted subsurface drain PVC per ASTM D1785 SCH 40. • Slots should be cut perpendicular to the long axis of the pipe and be 0.04 to 0.069 inches by 1 inch long and be spaced 0.25 inches apart (spaced longitudinally). Slots should be arranged in four rows spaced on 45 -degree centers and cover'/2 of the circumference of the pipe. See Underdrain Aggregate Filter and Bedding Layer (below) for aggregate gradation appropriate for this slot size. • Underdrains should be sloped at a minimum of 0.5 percent unless otherwise specified by an engineer. Perforated PVC or flexible slotted HDPE pipe cannot be cleaned with pressurized water or root cutting equipment, are less durable and are not recommended. Wrapping the underdrain pipe in filter fabric increases chances of clogging and is not recommended. A 6 -inch rigid non -perforated observation pipe or other maintenance access should be connected to the underdrain every 250 to 300 feet to provide a clean-out port, as well as an observation well to monitor dewatering rates. Underdrain Aggregate Filter and Bedding Layer Aggregate filter and bedding layers buffer the underdrain system from sediment input and clogging. When properly selected for the soil gradation, geosynthetic filter fabrics can provide adequate protection from the migration of fines. However, aggregate filter and bedding layers, with proper gradations, provide a larger surface area for protecting underdrains and are preferred. Table V-5.3: Mineral Aggregate Gradation for Underdrain Filter and Bedding Layer Sieve size Percent Passing 3/4 inch 100 '/4 inch 30-60 US No. 8 20-50 US No. 50 3-12 US No. 200 0-1 Note: The above gradation is a Type 26 mineral aggregate as detailed for gravel backfill for drains in the City of Seattle Standard Specifications for Road, Bridge, and Municipal Construction ,(Seattle Public Utilities, 2014). https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 19/25 12/21/2020 BMP T7.30: Bioretention Place the underdrain pipe on a bed of the Type 26 aggregate with a minimum thickness of 6 inches and cover with Type 26 aggregate to provide a 1 -foot minimum depth around the top and sides of the slotted pipe. See the Low Impact Development Technical Guidance Manual for Puget Sound .(Hinman and Wulkan, 2012). Orifice and Other Flow Control sStructures The minimum orifice diameter should be 0.5 inches to minimize clogging and maintenance requirements. Check Dams and Weirs Check dams are necessary for reducing flow velocity and potential erosion, as well as increasing detention time and infiltration capability on sloped sites. Typical materials include concrete, wood, rock, compacted dense soil covered with vegetation, and vegetated hedge rows. Design depends on Flow Control goals, local regulations for structures within road right-of-ways and aesthetics. Optimum spacing is determined by Flow Control benefit (modeling) in relation to cost consideration. See the Low Impact Development Technical Guidance Manual for Puget Sound .(Hinman and Wulkan, 2012) for displays of typical designs. UIC Discharge Stormwater that has passed through the bioretention soil mix may also discharge to a gravel -filled dug or drilled drain. Underground Injection Control (UIC) regulations are applicable and must be followed (Chapter 173-218 WAC). See 1-4 UIC Program. Hydraulic Restriction Layers: Adjacent roads, foundations or other infrastructure may require that infiltration pathways are restricted to prevent excessive hydrologic loading. Two types of restricting layers can be incorporated into bioretention designs: • Clay (bentonite) liners are low permeability liners. Where clay liners are used underdrain systems are necessary. See V-1.3.3 Low Permeability Liners for guidelines. • Geomembrane liners completely block infiltration to subgrade soils and are used for ground water protection when bioretention BMPs are installed to filter storm flows from pollutant hotspots or on sidewalls of bioretention areas to restrict lateral flows to roadbeds or other sensitive infrastructure. Where geomembrane liners are used to line the entire BMP, underdrain systems are necessary. See V-1.3.3 Low Permeability Liners for guidelines. Plant Materials In general, the predominant plant material utilized in bioretention areas are species adapted to stresses associated with wet and dry conditions. Soil moisture conditions will vary within the facility from saturated (bottom of cell) to relatively dry (rim of cell). Accordingly, wetland plants may be used in the lower areas, if saturated soil conditions exist for appropriate periods, and drought -tolerant species planted on the perimeter of the facility or on mounded areas. See the Low Impact Development Technical Guidance Manual for Puget Sound .(Hinman and https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/2019SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 20/25 12/21/2020 BMP T7.30: Bioretention Wulkan, 2012) for additional guidance and recommended plant species. See also City of Seattle's ROW bioretention plant lists found in Seattle's GSI Manual, Appendix G, at the following web address: https://www.seattle.gov/util/cs/groups/public/@spu/@engineering/documents/webcontent/1 079167.pdf The side slopes for the bioretention facility (vertical or sloped) can affect the plant selection and must be considered. Additionally, trees can be planted along the side slopes or bottom of bioretention cells that are unlined. Mulch Layer You can design bioretention areas with or without a mulch layer. When used, mulch shall be: • Medium compost in the bottom of the BMP (compost is less likely to float during cell inundation). Compost shall not include biosolids or manures. • Shredded or chipped hardwood or softwood on side slopes above ponding elevation and rim area. Arborist mulch is mostly woody trimmings from trees and shrubs and is a good source of mulch material. Wood chip operations are a good source for mulch material that has more control of size distribution and consistency. Do not use shredded construction wood debris or any shredded wood to which preservatives have been added. • Free of weed seeds, soil, roots and other material that is not bole or branch wood and bark. • A maximum of 2 to 3 inches thick. Mulch shall not be: • Grass clippings (decomposing grass clippings are a source of nitrogen and are not recommended for mulch in bioretention areas). • Pure bark (bark is essentially sterile and inhibits plant establishment). In bioretention areas where higher flow velocities are anticipated, an aggregate mulch may be used to dissipate flow energy and protect underlying bioretention soil mix. Aggregate mulch varies in size and type, but 1 to 1 1/2 inch gravel (rounded) decorative rock is typical. Runoff Model Representation Note that if the project is using bioretention to only meet The List Approach within 1-3.4.5 MRS: On -Site Stormwater Management, there is no need to model the bioretention in a continuous runoff model. Size the bioretention as described above in Ponding Area. The guidance below is to show compliance with the LID Performance Standard in 1-3.4.5 MR5: On -Site Stormwater Management, or the standards in 1-3.4.6 MR6: Runoff Treatment, 1-3.4.7 MR7: Flow Control, and/or 1- 3.4.8 MR8: Wetlands Protection. Continuous runoff modeling software include modeling elements for bioretention. https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 21/25 12/21/2020 BMP T7.30: Bioretention The equations used by the elements are intended to simulate the wetting and drying of soil as well as how the soils function once they are saturated. This group of LID elements uses the modified Green Ampt equation to compute the surface infiltration into the amended soil. The water then moves through the top amended soil layer at the computed rate, determined by Darcy's and Van Genuchten's equations. As the soil approaches field capacity (i.e., gravity head is greater than matric head), the model determines when water will begin to infiltrate into the second soil layer (lower layer). This occurs when the matric head is less than the gravity head in the first layer (top layer). The second layer is intended to prevent loss of the amended soil layer. As the second layer approaches field capacity, the water begins to move into the third layer — the gravel underlayer. For each layer, the user inputs the depth of the layer and the type of soil. Within the WWHM continuous runoff model, for the Ecology -recommended soil specifications for each layer in the design criteria for bioretention, the model will automatically assign pre -determined appropriate values for parameters that determine water movement through that soil. These include: wilting point, minimum hydraulic conductivity, maximum saturated hydraulic conductivity, and the Van Genuchten number. For bioretention with underlying perforated drain pipes that discharge to the surface, the only volume available for storage (and modeled as storage as explained herein) is the void space within the aggregate bedding layer below the invert of the drain pipe. Use 40% void space for the Type 26 mineral aggregate specified in Underdrain .(optional) (above). Modeling: It is preferable to enter each bioretention device and its drainage area into the approved computer models for estimating their performance. However, where site layouts involve multiple bioretention facilities, the modeling schematic can become extremely complicated or not accommodated by the available schematic grid. In those cases, multiple bioretention facilities with similar designs (i.e., soil depth, ponding depth, freeboard height, and drainage area to ponding area ratio), and infiltration rates (Ecology suggests within a factor of 2) may have their drainage areas and ponded areas be combined, and represented in the runoff model as one drainage area and one bioretention device. In this case, use a weighted average of the design infiltration rates at each location. The averages are weighted by the size of their drainage areas. For bioretention with side slopes of 3H:1 V or flatter, infiltration through the side slope areas can be significant. Where side slopes are 3H:1 V or flatter, bioretention can be modeled allowing infiltration through the side slope areas to the native soil. In WWHM, modeling of infiltration through the side slope areas is accomplished by switching the default setting for "Use Wetted Surface Area (sidewalls): from "NO" to "YES." Installation Criteria Excavation Soil compaction can lead to bioretention BMP failure; accordingly, minimizing compaction of the base and sidewalls of the bioretention area is critical. Excavation should never be allowed during wet or saturated conditions (compaction can reach depths of 2-3 feet during wet conditions and mitigation is likely to not be https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 22/25 12/21/2020 BMP T7.30: Bioretention possible). Excavation should be performed by machinery operating adjacent to the bioretention BMP, and no heavy equipment with narrow tracks, narrow tires, or large lugged, high pressure tires should be allowed on the bottom of the bioretention BMP. If machinery must operate in the bioretention area for excavation, use light weight, low ground -contact pressure equipment and rip the base at completion to refracture soil to a minimum of 12 inches. If machinery operates in the BMP footprint, subgrade infiltration rates must be field tested and compared to initial Ksat tests obtained during design. Failure to meet or exceed the initial Ksat tests will require revised engineering designs to verify achievement of Runoff Treatment and Flow Control benefits that were estimated in the Stormwater Site Plan. Prior to placement of the bioretention soil mix, the finished subgrade shall: • Be scarified to a minimum depth of 3 inches. • Have any sediment deposited from construction runoff removed. To remove all introduced sediment, subgrade soil should be removed to a depth of 3-6 inches and replaced with bioretention soil mix. • Be inspected by the responsible engineer to verify required subgrade condition. Sidewalls of the BMP, beneath the surface of the bioretention soil mix, can be vertical if soil stability is adequate. Exposed sidewalls of the completed bioretention area with bioretention soil mix in place should be no steeper than 3H:1V. The bottom of the BMP should be flat. Soil Placement On-site soil mixing or placement shall not be performed if bioretention soil mix or subgrade soil is saturated. The bioretention soil mix should be placed and graded by machinery operating adjacent to the bioretention BMP. If machinery must operate in the bioretention cell for soil placement, use light weight equipment with low ground - contact pressure. If machinery operates in the BMP footprint, subgrade infiltration rates must be field tested and compared to initial Ksat tests obtained during design. Failure to meet or exceed the initial Ksat tests will require revised engineering designs to verify achievement of Runoff Treatment and Flow Control benefits that were estimated in the Stormwater Site Plan. The soil mixture shall be placed in horizontal layers not to exceed 6 inches per lift for the entire area of the bioretention BMP. Compact the bioretention soil mix to a relative compaction of 85 percent of modified maximum dry density (ASTM D 1557). Compaction can be achieved by boot packing (simply walking over all areas of each lift), and then apply 0.2 inches (0.5 cm) of water per 1 inch (2.5 cm) of bioretention soil mix depth. Water for settling should be applied by spraying or sprinkling. Temporary Erosion and Sediment Control JESC). Controlling erosion and sediment are most difficult during clearing, grading, and construction; accordingly, minimizing site disturbance to the greatest extent practicable is the most effective sediment management. During construction: https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 23/25 12/21/2020 BMP T7.30: Bioretention • Bioretention BMPs should not be used as sediment control BMPs, and all drainage should be directed away from bioretention BMPs after initial rough grading. Flow can be directed away from the BMP with temporary diversion swales or other approved protection. If introduction of construction runoff cannot be avoided see below for guidelines. • Construction on bioretention BMPs should not begin until all contributing drainage areas are stabilized according to erosion and sediment control BMPs and to the satisfaction of the engineer. • If the design includes curb and gutter, the curb cuts and inlets should be blocked until bioretention soil mix and mulch have been placed and planting completed (when possible), and dispersion pads are in place. Every effort during design, construction sequencing and construction should be made to prevent sediment from entering bioretention BMPs. However, bioretention areas are often distributed throughout the project area and can present unique challenges during construction. See the Low Impact Development Technical Guidance Manual for Puget Sound .(Hinman and Wulkan, 2012) for guidelines if no other options exist and runoff during construction must be directed through the bioretention BMPs. Erosion and sediment control practices must be inspected and maintained on a regular basis. Verification If using the default bioretention soil mix, pre -placement laboratory analysis for saturated hydraulic conductivity of the bioretention soil mix is not required. Verification of the mineral aggregate gradation, compliance with the compost specifications, and the mix ratio must be provided. If using a custom bioretention soil mix, verification of compliance with the minimum design criteria cited above for such custom mixes must be provided. This will require laboratory testing of the material that will be used in the installation. Testing shall be performed by a Seal of Testing Assurance, AASHTO, ASTM or other standards organization accredited laboratory with current and maintained certification. Samples for testing must be supplied from the bioretention soil mix that will be placed in the bioretention areas. If testing infiltration rates is necessary for post -construction verification, use the Pilot Infiltration Test (PIT) method or a double ring infiltrometer test (or other small-scale testing allowed by the local government with jurisdiction). If using the PIT method, do not excavate the bioretention soil mix (conduct the test at the elevation of the finished bioretention soil mix), use a maximum of 6 inch ponding depth and conduct the test before plants are installed. Maintenance Bioretention areas require annual plant, soil, and mulch layer maintenance to ensure optimum infiltration, storage, and pollutant removal capabilities. In general, bioretention maintenance requirements are typical landscape care procedures and include: • Watering: Plants should be selected to be drought tolerant and not require watering after establishment (2 to 3 years). Watering may be required during prolonged dry periods after plants are established. • Erosion control: Inspect flow entrances, ponding area, and surface overflow areas periodically, and replace soil, plant material, and/or mulch layer in areas if erosion has occurred. Properly designed BMPs with https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/2019SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 24/25 12/21/2020 BMP T7.30: Bioretention appropriate flow velocities should not have erosion problems except perhaps in extreme events. If erosion problems occur, the following should be reassessed: (1) flow volumes from contributing areas and bioretention cell sizing; (2) flow velocities and gradients within the cell; and (3) flow dissipation and erosion protection strategies in the pretreatment area and flow entrance. If sediment is deposited in the bioretention area, immediately determine the source within the contributing area, stabilize, and remove excess surface deposits. • Sediment removal: Follow the maintenance plan schedule for visual inspection and remove sediment if the volume of the ponding area has been compromised. • Plant material: Depending on aesthetic requirements, occasional pruning and removing dead plant material may be necessary. Replace all dead plants and if specific plants have a high mortality rate, assess the cause and replace with appropriate species. Periodic weeding is necessary until plants are established. • Weeding: Invasive or nuisance plants should be removed regularly and not allowed to accumulate and exclude planted species. At a minimum, schedule weeding with inspections to coincide with important horticultural cycles (e.g., prior to major weed varieties dispersing seeds). Weeding should be done manually and without herbicide applications. The weeding schedule should become less frequent if the appropriate plant species and planting density are used and the selected plants grow to capture the site and exclude undesirable weeds. • Nutrient and pesticides: The soil mix and plants are selected for optimum fertility, plant establishment, and growth. Nutrient and pesticide inputs should not be required and may degrade the pollutant processing capability of the bioretention area, as well as contribute pollutant loads to receiving waters. By design, bioretention BMPs are located in areas where phosphorous and nitrogen levels may be elevated and these should not be limiting nutrients. If in question, have soil analyzed for fertility. • Mulch: Replace mulch annually in bioretention BMPs where heavy metal deposition is high (e.g., contributing areas that include gas stations, ports and roads with high traffic loads). In residential settings or other areas where metals or other pollutant loads are not anticipated to be high, replace or add mulch as needed (likely 3 to 5 years) to maintain a 2 to 3 inch depth. • Soil: Soil mixes for bioretention BMPs are designed to maintain long-term fertility and pollutant processing capability. Estimates from metal attenuation research suggest that metal accumulation should not present an environmental concern for at least 20 years in bioretention systems, but this will vary according to pollutant load. Replacing mulch media in bioretention BMPs where heavy metal deposition is likely provides an additional level of protection for prolonged performance. If in question, have soil analyzed for fertility and pollutant levels. Refer to Appendix V-A: BMP Maintenance Tables for additional maintenance guidelines. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWMMWW/2019SWMMWW.htm#Topics/VolumeV/infiltrationBMPs/BMPt730.htm%3FToc... 25/25 Edge of pavement or curb -cut 2" woodchip mulch or aggregate Provide a 1" drop from the edge of pavement Overflow structure or flow path Notes: 1. Scarify subgrade 3" min. before bioretention soil installation 2. Compact BSM to 85% per ASTM 1577 DEPARTMENT OF ECOLOGY State of Washington BSM bottom width varies, V minimum Ponding depth Provide a 1" drop from the edge of sidewalk 1� / 6" min. freeboard Minimum separation varies, see design guidance Sidewalk LI- 11 I I I I—Irl� 2" woodchip mulch or aggregate 3" coarse compost in ponding area 18" Bioretention Soil Mix (BSM) Seasonal high water table, bedrock, or other impervious layer Typical Bioretention NOT TO SCALE Revised January 2019 Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. Edge of pavement or curb -cut 2" woodchip mulch or aggregate Provide a 1" drop from the edge of pavement Overflow structure or flow path 6" to 12" (see note 3) BSM bottom width varies, 1' minimum Ponding depth ��varies Provide a 1" drop from the edge of sidewalk 6" min. freeboard 6" (see note 4) Mineral aggregate bottom width to match BSM bottom width Sidewalk III 2" woodchip mulch or aggregate 3" coarse compost in ponding area 18" Bioretention Soil Mix (BSM) Mineral aggregate Underdrain pipe Notes: 1. Scarify subgrade 3" min. before BSM installation 2. Compact BSM to 85% per ASTM 1577 3. Minimum 6" to discourage fines from entering the underdrain from the BSM. Maximum 12" to prevent unnecessary BMP depth from encroaching into the seasonal high ground water. 4. If depth to the seasonal high ground water allows, this distance may be larger. 5. When an underdrain is used, the design must ensure that the seasonal high ground water does not encroach into the BMP (including the mineral aggregate layer surrounding the underdrain pipe). waa Nno" DEPARTMENT OF ECOLOGY State of Washington NOT TO SCALE Typical Bioretention w/Underdrain Revised January 2019 Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. Provide a 1" drop from the edge of pavement Provide a 1" drop from the edge of sidewalk Notes: 1. Scarify subgrade 3" min. before bioretention soil installation 2. Compact BSM to 85% per ASTM 1577 DEPARTMENT OF ECOLOGY State of Washington NOT TO SCALE Typical Bioretention w/Liner (Not LID) Revised January 2019 Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. gutter 6" Plan View NOT TO SCALE MINr DEPARTMENT OF ECOLOGY State of Washington DESIGNER INFORMATION: 1. 3 o N > d - `�►subgradei a �d a ° 4" not driane aCh ($e d ;h for sidewalk 2. a hannel & grate10 seenote 2) Bioretention each facility. Provide stations and/or •V dimensions and elevations at every inlet, W W W W W W ;ck dam sidewalk notch. note 2) 3. Longitudinal slope of planter matches road. W W CU W EL W W Sidewalk elevation must be set above inlet and outlet elevations to allow overflow to a� � U) drain to street before sidewalk. a Minimum interior planter width is 3 feet. A a d 4" thick i splash p a 4 o a ° Concre d � ° a a a a e d a a D d a G Q d C Sidewalk W W W W W W W W W W W W W W W 6. Existing utility lines must be sleeved or a relocated. Proposed utility lines to be located out of the facility. 7. m in fetal inlet '-0" ty . d 3 o c 3d at inlet constraints. 8. May use concrete or pavers. %=I W W W W W W W W W W W �'-R" Curb u. 3'-0' min. I I gutter 6" Plan View NOT TO SCALE MINr DEPARTMENT OF ECOLOGY State of Washington DESIGNER INFORMATION: 1. Adapt plan view example to your `�►subgradei engineered design. ;h for sidewalk 2. Include beginning and ending stations for Bioretention each facility. Provide stations and/or ge, as necessary dimensions and elevations at every inlet, outlet, check dam, planter corner and ;ck dam sidewalk notch. note 2) 3. Longitudinal slope of planter matches road. 4. Sidewalk elevation must be set above inlet and outlet elevations to allow overflow to \ drain to street before sidewalk. 5. Minimum interior planter width is 3 feet. A minimum of 4 feet interior planter width is required for street trees in planter. 6. Existing utility lines must be sleeved or relocated. Proposed utility lines to be located out of the facility. 7. Area and depth of facility are based upon :oncrete engineering calculations and right-of-way 3d at inlet constraints. 8. May use concrete or pavers. e or pavers 6., Concrete or pavers (to be specified by ---- designer) a Curb and gutter (by others) Finished - grade of planter +-d- 2'-6" y - Existing `�►subgradei Bioretention Soil Mix Open graded aggregate (when required) Sidewalk drainage notch to be 1" lower Top of wall at than sidewalk, end of planter sloped to facility 4" min. exposed 12" max T wall a Planter wall 6" benchfor • Section 1 1 construction Example of a Bioretention Planter Revised October 2016 Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. Attachment M Flow Control BMPs 12/21/2020 BMP T7.20: Infiltration Trenches You are here: 2019 SWMMWW > Volume V - Runoff Treatment, Flow Control, and LID BMP Library_ > V-5 Infiltration BMPs > BMP T7.20: Infiltration Trenches BMP T7.20: Infiltration Trenches Infiltration trenches are generally at least 24 inches wide, and are backfilled with a coarse stone aggregate, allowing for temporary storage of stormwater runoff in the voids of the aggregate material. Stored runoff then gradually infiltrates into the surrounding soil. The surface of the trench can be covered with grating and/or consist of stone, gabion, sand, or a grassed or asphalt area with a surface inlet. Perforated rigid pipe of at least 8 -inch diameter can also be used to distribute the stormwater in an infiltration trench. Underground Injection Control (UIC) regulations apply to infiltration trenches when perforated pipe is used, and then, provided that the design, operation, and maintenance criteria in this section are met, only the registration requirement applies. Where perforated pipe is not used, the registration requirement does not apply. See 1-4 UIC Program for details. If this BMP is proposed to be used for Runoff Treatment, the design must show that the criteria for Runoff Treatment in V-5.6 Site Suitability Criteria (SSC) are met. Refer to the guidance earlier in this chapter for information pertinent to all infiltration BMPs. Guidance specific to infiltration trenches is provided below. Figure V-5.5: Schematic of an Infiltration Trench pdf download Figure V-5.6: Parking Lot Perimeter Trench Design pdf download Figure V-5.7: Median Strip Trench Design https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWMMWW/2019SWMMWW.htm#Topics/VolumeV/infiltrationBMPs/BMPt720.htm%3FTocP... 1/4 12/21/2020 pdf download pdf download BMP T7.20: Infiltration Trenches Figure V-5.8: Oversized Pipe Trench Design .... Figure V-5.9: Swale/Trench Design tAf pdf download ...... Figure V-5.10: Underground Trench with Oil/Grit Chamber pdf download Design Criteria • Due to accessibility and maintenance limitations, carefully design and construct infiltration trenches. Contact the local jurisdiction for additional specifications. • Consider including an access port or open or grated top for accessibility to conduct inspections and maintenance. • Backfill Material - The aggregate material for the infiltration trench should consist of a clean aggregate with a maximum diameter of 3 inches and a minimum diameter of 1.5 inches. Void space for these aggregates should be in the range of 30 to 40 percent. • Geotextile fabric liner — Completely encase the aggregate fill material in an engineering geotextile material. Geotextile should surround all of the aggregate fill material except for the top one -foot, which is placed over the geotextile. Carefully select geotextile fabric with acceptable properties to avoid plugging (see V-1.3.4 Geotextile Specifications). • The bottom sand or geotextile fabric as shown in Figure V-5.11: Observation Well Details is optional. https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt720. htm%3FTocP... 2/4 12/21/2020 BMP T7.20: Infiltration Trenches Refer to the Geosynthetic Design and Construction Guidelines Participant Notebook _(Holtz et al., 1998) for design guidance on geotextiles in drainage applications. Refer to Long -Term Performance of Geosynthetics in Drainage Applications .(Koerner et al., 1994) for long-term performance data and background on the potential for geotextiles to clog, blind, or to allow piping to occur and how to design for these issues. • Overflow Channel - Because an infiltration trench is generally used for small drainage areas, an emergency spillway is not necessary. However, provide a non-erosive overflow channel leading to a stabilized watercourse. • Surface Cover - A stone filled trench can be placed under a porous or impervious surface cover to conserve space. • Observation Well - Install an observation well at the lower end of the infiltration trench to check water levels, drawdown time, sediment accumulation, and conduct water quality monitoring. Figure V-5.11: Observation Well Details illustrates observation well details. It should consist of a perforated PVC pipe which is 4 to 6 inches in diameter and it should be constructed flush with the ground elevation. For larger trenches a 12-36 inch diameter well can be installed to facilitate maintenance operations such as pumping out the sediment. Cap the top of the well to discourage vandalism and tampering. Construction Criteria • Trench Preparation - Place excavated materials away from the trench sides to enhance trench wall stability. Take care to keep this material away from slopes, neighboring property, sidewalks and streets. It is recommended that this material be covered with plastic. (See BMP C123: Plastic Covering). • Stone Aggregate Placement and Compaction - Place stone aggregate in lifts and compact using plate compactors. In general, a maximum loose lift thickness of 12 inches is recommended. The compaction process ensures geotextile conformity to the excavation sides, thereby reducing potential piping and geotextile clogging, and settlement problems. • Potential Contamination - Prevent natural or fill soils from intermixing with the stone aggregate. Remove all contaminated stone aggregate and replaced with uncontaminated stone aggregate. • Overlapping and Covering - Following the stone aggregate placement, fold the geotextile over the stone aggregate to form a 12 inch minimum longitudinal overlap. When overlaps are required between rolls, the upstream roll should overlap a minimum of 2 feet over the downstream roll in order to provide a shingled effect. • Voids behind Geotextile - Voids between the geotextile and excavation sides must be avoided. Removing boulders or other obstacles from the trench walls is one source of such voids. Place natural soils in these voids at the most convenient time during construction to ensure geotextile conformity to the excavation sides. This remedial process will avoid soil piping, geotextile clogging, and possible surface subsidence. • Unstable Excavation Sites - Vertically excavated walls may be difficult to maintain in areas where the soil moisture is high or where soft or cohesionless soils predominate. Trapezoidal, rather than rectangular, cross-sections may be needed. https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt720. htm%3FTocP... 3/4 12/21/2020 Maintenance Criteria BMP T7.20: Infiltration Trenches Monitor sediment buildup in the top foot of stone aggregate or the surface inlet on the same schedule as the observation well. pdf download Figure V-5.11: Observation Well Details Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No. 19-10-021 https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWMMWW/2019SWMMWW.htm#Topics/VolumeV/infiltrationBMPs/BMPt720.htm%3FTocP... 4/4 Wellcap Observation well � W /. O O OW O O O W \W v �W .✓ � ✓ � W W W W Emergency overflow berm Runoff filters through 20 foot W W W y y W W W W wide grass buffer strip W Protective layer of filter fabric I 111111110 0 0 0 0 0 0 � Trench 3-8 feet deep filled with 1.5 - 2.5 inch diameter clean stone Runoff exfiltrates through undisturbed subsoils Filter fabric lines si prevent soil contan <iTlI Sand filter 6-12 inches deep or fabric equivalent NOT TO SCALE 810 "go*& Schematic of an Infiltration Trench DEPARTMENT OF Revised May 2019 ECOLOGY State of Washington Side View Top View Dripline of tree should Berm (grassed) not extend over trench I i Slope of W I parking lot W W W W Slotted curbs act as Cars Q W a level spreader �r �WW n W -I- WW � W W Filter strip = trench = Removable directly abuts I=1 I I pavement -1 I protective filter W IIIIII IIIII W N W cloth layer W W W IIIIII III Storm drain I1=1 = 1=1=1 -11I-11I-11I-11I-11I- Optional sand filter Slotted curb spacers NOT TO SCALE �r Parking Lot Perimeter Trench Design "Mows Revised June 2016 DEPARTMENT OF ECOLOGYPlease see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, State of Washington limitation of liability, and disclaimer. Top View �r DEPARTMENT OF ECOLOGY State of Washington Side View 20' Grass filter strip Permeable filter fabric one foot below surface, traps debris Screened overflow pipe Outflow •_•61 _.. Sides lined with permeable filter fabric Clean washed stone or gravel (1.5 - 3.0 inch) 6 - 12 inch sand filter or permeable filter cloth lines bottom NOT TO SCALE Median Strip Trench Design Revised June 2016 Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. Section View / Removable impermeable Overflow pipe Observation well Oversized Pipe (Temporarily stores runoff) Removable permeable Plan View /— Observation well 0_ Overflow pipe 1.5 - 3.0 inch clean stone Holes drilled in underside of pipe Note: Alternative storage devices, such as plastic arches, are also acceptable in place of oversized pipe. DEPARTMENT OF ECOLOGY State of Washington Pretreatment facility Standard curb inlet MIN Modified two -chamber inlet NOT TO SCALE Oversized Pipe Trench Design Revised May 2019 Driveway culvert W Swale W . 21110 DEPARTMENT OF ECOLOGY State of Washington Top View Driveway culvert - - ■ • f i • • • • •-• •-• •-•-•-•- rj I I• I I I I I I 1 1 1 I' c�:�`f i�`f Y�`f i�`f i•`t sif si`f,if�•'f�•�`-1•`1`�� . flll�l nil � • J" � `' ' _ Illmll�. IIIA/'' 1m� • ` r t 1111�I�111►, Ir � Side View Slope of the trench Runoff Road Runoff should be less than 5% ��____ Permeable filter fabric lines sides and also at one foot trench depth 6 inch sand layer Exfiltration Swale/Trench Design NOT TO SCALE Revised June 2016 Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. Top View Stormdrain inlet Overflow pipe Manholes for clean-out access Three -chamber water quality inlet Side View 6 inch orifices �r DEPARTMENT OF ECOLOGY State of Washington Trash rack Inverted elbow Perforated pipe inlet Underground trench 6 inch sand layer NOT TO SCALE Underground Trench with Oil/Grit Chamber Revised June 2016 Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. 12/21/2020 BMP T7.30: Bioretention You are here: 2019 SWMMWW > Volume V - Runoff Treatment, Flow Control, and LID BMP Library_ > V-5 Infiltration BMPs > BMP T7.30: Bioretention BMP T7.30: Bioretention Purpose Ecology accepts bioretention as having the potential to meet 1-3.4.5 MRS: On -Site Stormwater Management, I- 3.4.6 MR6: Runoff Treatment and 1-3.4.7 MR7: Flow Control for the tributary drainage areas depending upon site conditions and sizing. The purpose of bioretention is to provide effective removal of many stormwater pollutants, and provide reductions in stormwater runoff quantity and surface runoff flow rates. Where the surrounding native soils have adequate infiltration rates, bioretention can provide both Runoff Treatment and Flow Control. Where the native soils have low infiltration rates, underdrain systems can be installed and the bioretention BMP can still be used as a Runoff Treatment BMP. However, designs utilizing underdrains provide less Flow Control benefits. Description Bioretention areas are shallow landscaped depressions, with a designed soil mix (the bioretention soil mix) and plants adapted to the local climate and soil moisture conditions, that receive stormwater from a contributing area. Bioretention uses the imported bioretention soil mix as a treatment medium. As in infiltration, the pollutant removal mechanisms include filtration, adsorption, and biological action. Bioretention BMPs can be built within earthen swales or placed within vaults. Water that has passed through the bioretention soil mix (or approved equivalent) may be discharged to the ground or collected and discharged to surface water. The term, bioretention, is used to describe various designs using soil and plant complexes to manage stormwater. The following terminology is used in this manual: • Bioretention cells: Shallow depressions with a designed planting soil mix and a variety of plant material, including trees, shrubs, grasses, and/or other herbaceous plants. Bioretention cells may or may not have an underdrain and are not designed as a conveyance system. • Bioretention swales: Incorporate the same design features as bioretention cells; however, bioretention swales are designed as part of a system that can convey stormwater when maximum ponding depth is exceeded. Bioretention swales have relatively gentle side slopes and ponding depths that are typically 6 to 12 inches. • Bioretention planters and planter boxes: Bioretention soil mix and a variety of plant material including trees, shrubs, grasses, and/or other herbaceous plants within a vertical walled container usually constructed from formed concrete, but could include other materials. Planter boxes are completely impervious and include a bottom (must include an underdrain). Planters have an open bottom and allow infiltration to the subgrade. These designs are often used in ultra -urban settings. https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/2019SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 1/25 12/21/2020 BMP T7.30: Bioretention Stormwater planters in the ROW require urban design and tailoring it to street typology and context. NACTO Urban Street Stormwater Guide provides guidance for designing roadside stormwater planters. httpa//nacto.org/publication/urban-street-stormwater-guide/ See Figure V-5.12: Typical Bioretention, Figure V-5.13: Typical Bioretention w/Underdrain, Figure V-5.14: Typical Bioretention w/Liner (Not LID), and Figure V-5.15: Example of a Bioretention Planter for examples of various types of bioretention configurations. Note: Ecology has approved use of certain manufactured treatment devices that use specific, high rate media for treatment. Such systems do not use bioretention soil mix, and are not considered a bioretention BMP (even though marketing materials for these manufactured treatment devices may compare them to bioretention). See V- 10 Manufactured Treatment Devices as BMPs for more information on manufactured treatment devices. Figure V-5.12: Typical Bioretention pdf download Figure V-5.13: Typical Bioretention w/Underdrain pdf download Figure V-5.14: Typical Bioretention w/Liner (Not LID) pdf download Figure V-5.15: Example of a Bioretention Planter pdf download https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 2/25 12/21/2020 BMP T7.30: Bioretention Applications and Limitations Because bioretention BMPs use an imported soil mix that has a moderate design infiltration rate, they are best applied for small drainages, and near the source of the stormwater runoff. Bioretention cells may be scattered throughout a subdivision; a bioretention swale may run alongside the access road; or a series of bioretention planter boxes may serve the road. In these situations, they can but are not required to fully meet the requirement to treat 91 % of the stormwater runoff file (the Water Quality Design Volume, as described in III -2.6 Sizing Your Runoff Treatment BMPs) from pollution -generating surfaces. The amount of stormwater that is predicted to pass through the bioretention soil mix is treated, and may be subtracted from the 91 % volume that must be treated to meet 1-3.4.6 MR6: Runoff Treatment. Downstream Runoff Treatment BMPs may be significantly smaller as a result. Bioretention BMPs that infiltrate into the ground can also provide significant Flow Control. They can, but are not required to fully meet the Flow Control Performance Standard of 1-3.4.7 MR7: Flow Control. Because they typically do not have an orifice restricting overflow or underflow discharge rates, they typically don't fully meet 1-3.4.7 MR7: Flow Control. However, their performance contributes to meeting the standard, and that can result in much smaller additional Flow Control BMPs at the bottom of the project site. Bioretention can also help achieve compliance with the LID Performance Standard of 1-3.4.5 MRS: On -Site Stormwater Management. Bioretention constructed with imported composted material should not be used within one-quarter mile of phosphorus -sensitive waterbodies if the underlying native soil does not meet the criteria for Runoff Treatment per V-5.6 Site Suitability Criteria (SSC). Preliminary monitoring indicates that new bioretention BMPs can add phosphorus to stormwater. Therefore, they should also not be used with an underdrain when the underdrain water would be routed to a phosphorus -sensitive receiving water. Applications with or without underdrains vary extensively and can be applied in new development, redevelopment and retrofits. Typical applications include: • Individual lots for rooftop, driveway, and other on -lot impervious surfaces. • Shared facilities located in common areas for individual lots. • Areas within loop roads or cul-de-sacs. • Landscaped parking lot islands. • Within right-of-ways along roads (often linear bioretention swales or cells). • Common landscaped areas in apartment complexes or other multifamily housing designs. • Planters on building roofs, patios, and as part of streetscapes. Infeasibility Criteria The following infeasibility criteria describe conditions that make bioretention infeasible when applying The List Approach within 1-3.4.5 MR5: On -Site Stormwater Management. If a project proponent wishes to use a https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 3/25 12/21/2020 BMP T7.30: Bioretention bioretention BMP even though one of the infeasibility criteria within this section are met„ they may propose a functional design to the local government. Criteria with setback distances are as measured from the bottom edge of the bioretention soil mix. Any of the following circumstances allow the designer to determine bioretention as "infeasible" when applying the The List Approach within 1-3.4.5 MRS: On -Site Stormwater Management: • Citation of any of the following infeasibility criteria must be based on an evaluation of site-specific conditions and a written recommendation from an appropriate licensed professional (e.g., engineer, geologist, hydrogeologist): o Where professional geotechnical evaluation recommends infiltration not be used due to reasonable concerns about erosion, slope failure, or down gradient flooding. o Within an area whose ground water drains into an erosion hazard, or landslide hazard area. o Where the only area available for siting would threaten the safety or reliability of pre-existing underground utilities, pre-existing underground storage tanks, pre-existing structures, or pre-existing road or parking lot surfaces. o Where the only area available for siting does not allow for a safe overflow pathway to the municipal separate storm sewer system or private storm sewer system. o Where there is a lack of usable space for bioretention BMPs at re -development sites, or where there is insufficient space within the existing public right-of-way on public road projects. o Where infiltrating water would threaten existing below grade basements. o Where infiltrating water would threaten shoreline structures such as bulkheads. • The following infeasibility criteria are based on conditions such as topography and distances to predetermined boundaries. Citation of the following criteria do not need site-specific written recommendations from a licensed professional, although some may require professional services to determine: o Within setbacks from structures as established by the local government with jurisdiction. o Where they are not compatible with the surrounding drainage system as determined by the local government with jurisdiction (e.g., project drains to an existing stormwater collection system whose elevation or location precludes connection to a properly functioning bioretention BMP) o Where land for bioretention is within area designated as an erosion hazard or landslide hazard. o Where the site cannot be reasonably designed to locate bioretention BMPs on slopes less than 8%. o Within 50 feet from the top of slopes that are greater than 20% and over 10 feet of vertical relief. o For properties with known soil or ground water contamination (typically federal Superfund sites or state cleanup sites under the Model Toxics Control Act (MTCA)): https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 4/25 12/21/2020 BMP T7.30: Bioretention ■ Within 100 feet of an area known to have deep soil contamination; ■ Where ground water modeling indicates infiltration will likely increase or change the direction of the migration of pollutants in the ground water; ■ Wherever surface soils have been found to be contaminated unless those soils are removed within 10 horizontal feet from the infiltration area; ■ Any area where these BMPs are prohibited by an approved cleanup plan under the state Model Toxics Control Act or Federal Superfund Law, or an environmental covenant under Chapter 64.70 RCW. o Within 100 feet of a closed or active landfill. o Within 100 feet of a drinking water well, or a spring used for drinking water supply. o Within 10 feet of small on-site sewage disposal drainfield, including reserve areas, and grey water reuse systems. For setbacks from a "large on-site sewage disposal system", see Chapter 246-272B WAC. o Within 10 feet of an underground storage tank and connecting underground pipes when the capacity of the tank and pipe system is 1100 gallons or less. (As used in these criteria, an underground storage tank means any tank used to store petroleum products, chemicals, or liquid hazardous wastes of which 10% or more of the storage volume (including volume in the connecting piping system) is beneath the ground surface. o Within 100 feet of an underground storage tank and connecting underground pipes when the capacity of the tank and pipe system is greater than 1100 gallons. o Where the minimum vertical separation of 1 foot to the seasonal high water table, bedrock, or other impervious layer would not be achieved below bioretention that would serve a drainage area that is less than: 1. 5,000 sq. ft. of pollution -generating impervious surface, and 2. 10,000 sq. ft. of impervious surface, and 3. three-quarter (3/4) acres of pervious surface. o Where the minimum vertical separation of 3 feet to the seasonal high water table, bedrock, or other impervious layer would not be achieved below bioretention that would serve a drainage area that meets or exceeds: AND 1. 5,000 sq. ft. of pollution -generating impervious surface, or 2. 10,000 sq. ft. of impervious surface, or 3. three-quarter (3/4) acres of pervious surface. https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 5/25 12/21/2020 BMP T7.30: Bioretention cannot reasonably be broken down into amounts smaller than those listed in 1-3 (above). o Where the field testing indicates potential bioretention sites have a measured (a.k.a., initial) native soil saturated hydraulic conductivity less than 0.30 inches per hour. If the measured native soil infiltration rate is less than 0.30 in/hour, bioretention should not be used to meet the The List Approach of I-3.4.5 MRS: On -Site Stormwater Management. In these slow draining soils, a bioretention BMP with an underdrain may be used to treat pollution -generating surfaces to help meet I-3.4.6 MR6: Runoff Treatment. If the underdrain is elevated within a base course of gravel, the bioretention BMP will also provide some modest flow reduction benefit that will help achieve the LID Performance Standard within 1-3.4.5 MR5: On -Site Stormwater Management and/or the Flow Control Performance Standard within 1-3.4.7 MR7: Flow Control. • A local government may designate geographic boundaries within which bioretention BMPs may be designated as infeasible due to year-round, seasonal or periodic high groundwater conditions, or due to inadequate infiltration rates. Designations must be based upon a pre-ponderance of field data, collected within the area of concern, that indicate a high likelihood of failure to achieve the minimum ground water clearance or infiltration rates identified in the above infeasibility criteria. The local government must develop a technical report and make it available upon request to Ecology. The report must be authored by (a) professional(s) with appropriate expertise (e.g., registered engineer, geologist, hydrogeologist, or certified soil scientist), and document the location and the pertinent values/observations of data that were used to recommend the designation and boundaries for the geographic area. The types of pertinent data include, but are not limited to: o Standing water heights or evidence of recent saturated conditions in observation wells, test pits, test holes, and well logs. o Observations of areal extent and time of surface ponding, including local government or professional observations of high water tables, frequent or long durations of standing water, springs, wetlands, and/or frequent flooding. o Results of infiltration tests • In addition, a local government can map areas that meet a specific infeasibility criterion listed above provided they have an adequate data basis. Criteria that are most amenable to mapping are: o Where land for bioretention is within an area designated by the local government as an erosion hazard, or landslide hazard o Within 50 feet from the top of slopes that are greater than 20% and over 10 feet vertical relief o Within 100 feet of a closed or active landfill Design Criteria General Design Criteria https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 6/25 12/21/2020 BMP T7.30: Bioretention • Utility conflicts: Consult local jurisdiction requirements for horizontal and vertical separation required for publicly -owned utilities, such as water and sewer. Consult the appropriate franchise utility owners for separation requirements from their utilities, which may include communications and gas. When separation requirements cannot be met, designs should include appropriate mitigation measures, such as impermeable liners over the utility, sleeving utilities, fixing known leaky joints or cracked conduits, and/or adding an underdrain to the bioretention. • Transportation safety: The design configuration and selected plant types should provide adequate sight distances, clear zones, and appropriate setbacks for roadway applications in accordance with local jurisdiction requirements. • Ponding depth and surface water draw -down: Flow Control needs, as well as location in the development, and mosquito breeding cycles will determine draw -down timing. For example, front yards and entrances to residential or commercial developments may require rapid surface dewatering for aesthetics. In no case shall draw down time exceed 48 hours. • Impacts of surrounding activities: Human activity influences the location of the BMP in the development. For example, locate bioretention BMPs away from traveled areas on individual lots to prevent soil compaction and damage to vegetation or provide elevated or bermed pathways in areas where foot traffic is inevitable. Provide barriers, such as wheel stops, to restrict vehicle access in roadside applications. • Visual buffering: Bioretention BMPs can be used to buffer structures from roads, enhance privacy among residences, and for an aesthetic site feature. • Site growing characteristics and plant selection: Appropriate plants should be selected for sun exposure, soil moisture, and adjacent plant communities. Native species or hardy cultivars are recommended and can flourish in the properly designed and placed bioretention soil mix with no nutrient or pesticide inputs and 2-3 years irrigation for establishment. Invasive species and noxious weed control will be required as typical with all planted landscape areas. • Project submission requirements: Submit the results of infiltration (Ksat) testing and ground water elevation testing (or other documentation and justification for the rates and hydraulic restriction layer clearances) with the Stormwater Site Plan as justification for the feasibility decision regarding bioretention and as justification for assumptions made in the runoff modeling. • Legal documentation to track bioretention obligations: Where drainage plan submittals include assumptions with regard to size and location of bioretention BMPs, approval of the plat, short -plat, or building permit should identify the bioretention obligation of each lot; and the appropriate lots should have deed requirements for construction and maintenance of those BMPs • Much of the design criteria within this BMP originated from the Low Impact Development Technical Guidance Manual for Puget Sound .(Hinman and Wulkan, 2012). Refer to that document for additional explanations and background. Note that the Low Impact Development Technical Guidance Manual for Puget Sound .(Hinman and Wulkan, 2012) is for additional information purposes only. You must follow the guidance within this manual if there https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWMMWW/2019SWMMWW.htm#Topics/VolumeV/infiltrationBMPs/BMPt730.htm%3FToc... 7/25 12/21/2020 BMP T7.30: Bioretention are any discrepancies between this manual and the Low Impact Development Technical Guidance Manual for Puget Sound .(Hinman and Wulkan, 2012). • Geotechnical analysis is an important first step to develop an initial assessment of the variability of site soils, infiltration characteristics and the necessary frequency and depth of infiltration tests. See V-5.2 Infiltration BMP Design Steps. Determining the Native Soil Infiltration Rates Determining infiltration rates of the site soils is necessary to determine feasibility of designs that intend to infiltrate stormwater on-site. It is also necessary to estimate flow reduction benefits of such designs when using a continuous runoff model. The certified soils professional or engineer can exercise discretion concerning the need for and extent of infiltration rate (saturated hydraulic conductivity, Ksat) testing. The professional can consider a reduction in the extent of infiltration (Ksat) testing if, in their judgment, information exists confirming that the site is unconsolidated outwash material with high infiltration rates, and there is adequate separation from ground water. The following provides recommended tests for the soils underlying bioretention BMPs. The test should be run at the anticipated elevation of the top of the native soil beneath the bioretention BMP. Refer to V-5.4 Determining the Design Infiltration Rate of the Native Soils for further guidance on the methods to determine the infiltration rate of the native soils. • Small bioretention cells (bioretention BMPs made up of one or multiple cells that receive water from 1 or 2 individual lots or < 1/4 acre of pavement or other impervious surface) have the following options for determining the native soil infiltration rate: 1. Small-scale pilot infiltration test (PIT) as described in V-5.4 Determining the Design Infiltration Rate of the Native Soils. 2. If the site is underlain with soils not consolidated by glacial advance (e.g., recessional outwash soils), then the designer may use the grain size analysis method described in V-5.4 Determining the Design Infiltration Rate of the Native Soils based on the layer(s) identified in results of one soil test pit or boring. • Large bioretention cells (bioretention BMPs made up of one or multiple cells that receive water from several lots or 1/4 acre or more of pavement or other impervious surface) have the following options for determining the native soil infiltration rate: 1. Multiple small-scale or one large-scale PIT. If using the small-scale test, measurements should be taken at several locations within the area of interest. 2. If the site is underlain with soils not consolidated by glacial advance (e.g., recessional outwash soils), then the designer may use the grain size analysis method described in V-5.4 Determining the Design Infiltration Rate of the Native Soils. Use the grain size analysis method based on more than one soil test pit or boring. The more test pits/borings used, and the more evidence of consistency in the soils, the less of a correction factor may be used. https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWMMWW/2019SWMMWW.htm#Topics/VolumeV/infiltrationBMPs/BMPt730.htm%3FToc... 8/25 12/21/2020 BMP T7.30: Bioretention • Bioretention swales have the following options for determining the native soil infiltration rate: 1. Approximately 1 small-scale PIT per 200 feet of swale, and within each length of road with significant differences in subsurface characteristics. 2. If the site is underlain with soils not consolidated by glacial advance (e.g., recessional outwash soils), then the designer may use the grain size analysis method described in V-5.4 Determining the Design Infiltration Rate of the Native Soils. Approximately 1 soil test pit/boring per 200 feet of swale and within each length of road with significant differences in subsurface characteristics. • On a single, smaller commercial property, one bioretention BMP will likely be appropriate. In that case, a small-scale PIT — or an alternative small scale test specified by the local government - should be performed at the proposed bioretention location. Tests at more than one site could reveal the advantages of one location over another. On larger commercial sites, a small-scale PIT every 5,000 sq. ft. is advisable. If soil characteristics across the site are consistent, a geotechnical professional may recommend a reduction in the number of tests. • On multi -lot residential developments, multiple bioretention BMPs, or a BMP stretching over multiple properties are appropriate. In most cases, it is necessary to perform small-scale PITs, or other small-scale tests as allowed by the local jurisdiction. A test is advisable at each potential bioretention site. Long, narrow bioretention BMPs, such as one following the road right-of-way, should have a test location at least every 200 lineal feet, and within each length of road with significant differences in subsurface characteristics. If the site subsurface characterization, including soil borings across the development site, indicate consistent soil characteristics and depths to seasonal high ground water conditions or a hydraulic restriction layer, the number of test locations may be reduced to a frequency recommended by a geotechnical professional. After concluding an infiltration test, infiltration test sites should be over -excavated 3 feet below the projected bioretention BMP's bottom elevation unless minimum clearances to seasonal high ground water have or will be determined by another method. This overexcavation is to determine if there are restrictive layers or ground water. Observe whether water is infiltrating vertically or only spreading horizontally because of ground water or a restrictive soil layer. Observations through a wet season can identify a seasonal ground water restriction. If a single bioretention BMP serves a drainage area exceeding 1 acre, a ground water mounding analysis may be necessary in accordance with V-5.2 Infiltration BMP Design Steps. Assignment of Appropriate Correction Factors to the Native Soil If the design requires determination of a long-term (design) infiltration rate of the native soils (for example, to demonstrate compliance with the LID Performance Standard and/or the Flow Control Performance Standard), refer to V-5.4 Determining the Design Infiltration Rate of the Native Soils and the following additional guidance specific to bioretention BMPs: • The overlying bioretention soil mix provides excellent protection for the underlying native soil from sedimentation. Accordingly, when using The Simplified Approach to Calculating the Design Infiltration Rate of the Native Soils as described in V-5.4 Determining the Design Infiltration Rate of the Native Soils, the https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/2019SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 9/25 12/21/2020 BMP T7.30: Bioretention correction factor for the sub -grade soil does not have to take into consideration the extent of influent control and clogging over time. The correction factor to be applied to in-situ, small-scale infiltration test results for bioretention sites is determined by the site variability and number of locations tested as well as the method used to determine initial Ksat• Using Table V-5.1: Correction Factors to be Used With In -Situ Saturated Hydraulic Conductivity Measurements to Estimate Design Rates, the correction factor for bioretention design is revised based on this guidance as: Total Correction Factor, CFT = CFV x CFt • Tests should be located and be at an adequate frequency capable of producing a soil profile characterization that fully represents the infiltration capability where the bioretention areas are to be located. The partial correction factor CFV depends on the level of uncertainty that variable subsurface conditions justify. If a pilot infiltration test is conducted for all bioretention areas or the range of uncertainty is low (for example, conditions are known to be uniform through previous exploration and site geological factors) one pilot infiltration test may be adequate to justify a CFV of one. If the level of uncertainty is high, a CFV near the low end of the range may be appropriate. Two example scenarios where low CFVs may be appropriate include: o Site conditions are highly variable due to a deposit of ancient landslide debris, or buried stream channels. In these cases, even with many explorations and several pilot infiltration tests, the level of uncertainty may still be high. o Conditions are variable, but few explorations and only one pilot infiltration test is conducted. That is, the number of explorations and tests conducted do not match the degree of site variability anticipated. Determining the Bioretention Soil Mix Design Infiltration Rate 1. Determine the initial saturated hydraulic conductivity (Ksat) based on the type of bioretention soil mix, as follows: o If using Ecology's default bioretention soil mix (detailed below), the initial Ksat is 12 inches per hour (30.48 cm/hr). o If using a custom bioretention soil mix (per the guidance for custom mixes below), use ASTM D 2434 Standard Test Method for Permeability of Granular Soils (Constant Head) with a compaction rate of 85 percent using ASTM D1557 Test Method for Laboratory Compaction Characteristics of Soil Using Modified Effort. See the additional guidance below for specific procedures for conducting ASTM D 2434. The designer must enter the derived Ksat value into the continuous modeling software. 2. After determining the initial Ksat, determine the appropriate safety factor: o If the contributing area to the bioretention BMP is equal to or exceeds any of the following limitations: https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 10/25 12/21/2020 BMP T7.30: Bioretention o 5,000 square feet of pollution -generating impervious surface; o 10,000 square feet of impervious surface; o % acre of lawn and landscape, use 4 as the Ksat safety factor. o If the contributing area is less than all of the above areas, or if the design includes a pretreatment BMP for solids removal, use 2 as the Ksat safety factor. 3. The continuous runoff model has a field for entering Ksat and the appropriate safety factor. Recommended Modifications to ASTM D 2434 When Measuring Hydraulic Conductivity for Bioretention Soil Mixes Proctor method ASTM D1557 Method C (6 -inch mold) shall be used to determine maximum dry density values for compaction of the bioretention soil sample. Sample preparation for the Proctor test shall be amended in the following ways: 1. Maximum grain size within the sample shall be no more than '/2 inches in size. 2. Snip larger organic particles (if present) intol/2 inch long pieces. 3. When adding water to the sample during the Proctor test, allow the sample to pre-soak for at least 48 hours to allow the organics to fully saturate before compacting the sample. This pre-soak ensures the organics have been fully saturated at the time of the test. ASTM D2434 shall be used and amended in the following ways: 1. Apparatus: 2. Sample: a. 6 -inch mold size shall be used for the test. b. If using porous stone disks for the testing, the permeability of the stone disk shall be measured before and after the soil tests to ensure clogging or decreased permeability has not occurred during testing. c. Use the confined testing method, with 5- to 10 -pound force spring d. Use de -aired water. a. Maximum grain size within the sample shall not be more than '/2 inch in size. b. Snip larger organic particles (if present) into'/z-inch long pieces. c. Pre-soak the sample for at least 48 hours prior to loading it into the mold. During the pre- soak, the moisture content shall be higher than optimum moisture but less than full https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 11/25 12/21/2020 BMP T7.30: Bioretention saturation (i.e., there shall be no free water). This pre-soak ensures the organics have been fully saturated at the time of the test. 3. Preparation of Sample: a. Place soil in cylinder via a scoop. b. Place soil in 1 -inch lifts and compact using a 2 -inch -diameter round tamper. Pre -weigh how much soil is necessary to fill 1 -inch lift at 85% of maximum dry density, then tamp to 1 -inch thickness. Once mold is full, verify that density is at 85% of maximum dry density (+ or — 0.5%). Apply vacuum (20 inches Hg) for 15 minutes before inundation. c. Inundate sample slowly under a vacuum of 20 inches Hg over a period of 60 to 75 minutes. d. Slowly remove vacuum ( > 15 seconds). e. Sample shall be soaked in the mold for 24 to 72 hours before starting test. 4. Procedure: a. The permeability test shall be conducted over a range of hydraulic gradients between 0.1 and 2. b. Steady state flow rates shall be documented for four consecutive measurements before increasing the head. c. The permeability test shall be completed within one day (one -day test duration). Default Bioretention Soil Mix (BSM) Projects which use the following requirements for the bioretention soil mix do not have to test the mix for its saturated hydraulic conductivity (Ksat). See Determining the Bioretention Soil Mix Design Infiltration Rate. Mineral Aggregate for Default BSM Percent Fines: A range of 2 to 4 percent passing the #200 sieve is ideal and fines should not be above 5 percent for a proper functioning specification according to ASTM D422. Aggregate Gradation for Default BSM The aggregate portion of the BSM should be well -graded. According to ASTM D 2487-98 (Classification of Soils for Engineering Purposes (Unified Soil Classification System)), well -graded sand should have the following gradation coefficients: • Coefficient of Uniformity (Cu = D60/D10) equal to or greater than 4, and • Coefficient of Curve (Cc = (D30)2/D60 x D10) greater than or equal to 1 and less than or equal to 3. https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 12/25 12/21/2020 BMP T7.30: Bioretention Table V-5.2: General Guideline for Mineral Aggregate Gradation provides a gradation guideline for the aggregate component of the default bioretention soil mix .(Hinman, 2009). The sand gradation below is often supplied as a well -graded utility or screened. With compost this blend provides enough fines for adequate water retention, hydraulic conductivity within recommended range (see below), pollutant removal capability, and plant growth characteristics for meeting design guidelines and objectives. Table V-5.2: General Guideline for Mineral Aggregate Gradation Sieve Size Percent Passing 3/8" 100 #4 95-100 #10 75-90 #40 25-40 #100 4-10 #200 2-5 Where existing soils meet the above aggregate gradation, those soils may be amended rather than importing mineral aggregate. Compost to Aggregate Ratio, Organic Matter Content, and Cation Exchange Capacity for Default BSM • Compost to aggregate ratio: 60-65 percent mineral aggregate, 35 — 40 percent compost by volume. • Organic matter content: 5 — 8 percent by weight. • Cation Exchange Capacity (CEC) must be > 5 milliequivalents/100 g dry soil Note: Soil mixes meeting the above specifications do not have to be tested for CEC. They will readily meet the minimum CEC. Compost for Default BSM To ensure that the BSM will support healthy plant growth and root development, contribute to biofiltration of pollutants, and not restrict infiltration when used in the proportions cited herein, the following compost standards are required. • Meets the definition of "composted material" in WAC 173-350-100 and complies with testing parameters and other standards in WAC 173-350-220. • Produced at a composting facility that is permitted by the jurisdictional health authority. Permitted compost facilities in Washington are included in a spreadsheet titled Washington composting facilities and material types — 2017 at the following web address: https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/2019SWMMWW/2019SWMMWW.htm#Topics/VolumeV/InfiltrationBMPs/BMPt730.htm%3FToc... 13/25 12/21/2020 BMP T7.30: Bioretention httpa//ecology.wa.gov/Waste-Toxics/Reducing-recycling-waste/Organic-materials/Managing-organics- compost • The compost product must originate a minimum of 65 percent by volume from recycled plant waste comprised of "yard debris," "crop residues," and "bulking agents" as those terms are defined in WAC 173- 350-100. A maximum of 35 percent by volume of "post -consumer food waste" as defined in WAC 173-350- 100, but not including biosolids or manure, may be substituted for recycled plant waste. • Stable (low oxygen use and CO2 generation) and mature (capable of supporting plant growth) by tests shown below. This is critical to plant success in bioretention soil mixes. • Moisture content range: no visible free water or dust produced when handling the material. • Tested in accordance with the U.S. Composting Council "Test Method for the Examination of Compost and Composting" (TMECC), as established in the Composting Council's "Seal of Testing Assurance" (STA) program. Most Washington compost facilities now use these tests. • Screened to the following size gradations for Fine Compost when tested in accordance with TMECC test method 02.02-B, Sample Sieving for Aggregate Size Classification." Fine Compost shall meet the following gradation by dry weight Minimum percent passing 2": 100% Minimum percent passing 1": 99% Minimum percent passing 5/8": 90% Minimum percent passing 1/4": 75% • pH between 6.0 and 8.5 (TMECC 04.11-A). "Physical contaminants" (as defined in WAC 173-350-100) content less that 1 % by weight (TMECC 03.08-A) total, not to exceed 0.25 percent film plastic by dry weight. • Minimum organic matter content of 40% (TMECC 05.07-A "Loss on Ignition) • Soluble salt content less than 4.0 dS/m (mmhos/cm) (TMECC 04.10-A "Electrical Conductivity, 1:5 Slurry Method, Mass Basis") • Maturity indicators from a cucumber bioassay (TMECC 05.05-A "Seedling Emergence and Relative Growth ) must be greater than 80%for both emergence and vigor") • Stability of 7 mg CO2-C/g OM/day or below (TMECC 05.08-B "Carbon Dioxide Evolution Rate") • Carbon to nitrogen ratio (TMECC 05.02A "Carbon to Nitrogen Ratio" which uses 04.01 "Organic Carbon" and 04.02D "Total Nitrogen by Oxidation") of less than 25:1. The C:N ratio may be up to 35:1 for plantings composed entirely of Puget Sound Lowland native species and up to 40:1 for coarse compost to be used as a surface mulch (not in a soil mix). Custom Bioretention Soil Mix https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWMMWW/2019SWMMWW.htm#Topics/VolumeV/infiltrationBMPs/BMPt730.htm%3FToc... 14/25 12/21/2020 BMP T7.30: Bioretention Projects which prefer to create a custom bioretention soil mix rather than using the default bioretention soil mix described above must demonstrate compliance with the following criteria using the specified test method: • CEC >_ 5 meq/100 grams of dry soil; USEPA 9081 • pH between 5.5 and 7.0 • 5 - 8 percent organic matter content before and after the saturated hydraulic conductivity test; ASTM D2974 (Standard Test Method for Moisture, Ash, and Organic Matter of Peat and Other Organic Soils) • 2-5 percent fines passing the 200 sieve; TMECC 04.11-A • Measured (Initial) saturated hydraulic conductivity (Ksat) of less than 12 inches per hour; ASTM D 2434 (Standard Test Method for Permeability of Granular Soils (Constant Head)) at 85% compaction per ASTM D 1557 (Standard Test Method s for Laboratory Compaction Characteristics of Soil Using Modified Effort). Also, use Recommended Modifications to ASTM D 2434 When Measuring Hydraulic Conductivity for Bioretention Soil Mixes (as detailed above). • Design (long-term) saturated hydraulic conductivity of more than 1 inch per hour. Note: Design saturated hydraulic conductivity is determined by applying the appropriate infiltration correction factors as explained above under Determining the Bioretention Soil Mix Design Infiltration Rate. • If compost is used in creating the custom bioretention soil mix, it must meet all of the specifications listed above in Compost for Default BSM, except for the gradation specification. An alternative gradation specification must indicate the minimum percent passing for a range of similar particle sizes. Flow Entrance and Presettling Flow entrance design will depend on topography, flow velocities and volume entering the pretreatment and bioretention area, adjacent land use and site constraints. Flow velocities entering bioretention should be less than 1.0 ft/second to minimize erosion potential. Flow entrances should be placed with adequate separation from outlets to ensure that the influent stormwater is treated prior to reaching the overflow. Five primary types of flow entrances can be used for bioretention: • Dispersed, low velocity flow across a landscape area: Landscape areas and vegetated buffer strips slow incoming flows and provide an initial settling of particulates and are the preferred method of delivering flows to bioretention. Dispersed flow may not be possible given space limitations or if the BMP is controlling roadway or parking lot flows where curbs are mandatory. • Dispersed or sheet flow across pavement or gravel and past wheel stops for parking areas. • Curb cuts for roadside, driveway or parking lot areas: Curb cuts should include a rock pad, concrete or other erosion protection material in the channel entrance to dissipate energy. Minimum curb cut width should be 12 inches; however, 18 inches is recommended. The designer should calculate the size and choose the style of curb cut that is appropriate for the site conditions and runoff expectations. Avoid the use of angular rock or quarry spalls and instead use round (river) rock if needed. Removing sediment from angular rock is difficult. The flow entrance should slope steeply (at least 1:1) from the curb line to the bioretention, dropping https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 15/25 12/21/2020 BMP T7.30: Bioretention at least 3", and provide an area for settling and periodic removal of sediment and coarse material before flow dissipates to the remainder of the bioretention area. Curb cuts used for bioretention areas in high use parking lots or roadways require an increased level of maintenance due to high coarse particulates and trash accumulation in the flow entrance and associated bypass of flows. The following are methods recommended for areas where heavy trash and coarse particulates are anticipated: o Curb cut width: 18 inches. o At a minimum the flow entrance should drop 2 to 3 inches from the gutter line into the bioretention area and provide an area for settling and periodic removal of debris. o Anticipate relatively more frequent inspection and maintenance for areas with large impervious areas, high traffic loads and larger debris loads. o Catch basins or forebays may be necessary at the flow entrance to adequately capture debris and sediment load from large contributing areas and high use areas. Piped flow entrance in this setting can easily clog and catch basins with regular maintenance are necessary to capture coarse and fine debris and sediment. • Pipe flow entrance: Piped entrances should include rock or other erosion protection material in the channel entrance to dissipate energy and disperse flow. • Catch basin: In some locations where road sanding or higher than usual sediment inputs are anticipated, catch basins can be used to settle sediment and release water to the bioretention area through a grate for filtering coarse material. • Trench drains: Trench drains can be used to cross sidewalks or driveways where a deeper pipe conveyance creates elevation problems. Trench drains tend to clog and may require additional maintenance. Woody plants can restrict or concentrate flows and can be damaged by erosion around the root ball and should not be placed directly in the bioretention entrance flow path. Bottom Area and Side Slopes Bioretention areas are highly adaptable and can fit various settings such as rural and urban roadsides, ultra urban streetscapes and parking lots by adjusting bottom area and side slope configuration. Recommended maximum and minimum dimensions include: • Maximum planted side slope if total cell depth is greater than 3 feet: 3H:1 V. If steeper side slopes are necessary rockeries, concrete walls or soil wraps may be effective design options. Local jurisdictions may require bike and/or pedestrian safety features, such as railings or curbs with curb cuts, when steep side slopes are adjacent to sidewalks, walkways, or bike lanes. • Minimum bottom width for bioretention swales: 2 feet recommended and 1 foot minimum. Carefully consider flow depths and velocities, flow velocity control (check dams) and appropriate vegetation or rock mulch to prevent erosion and channelization at bottom widths less than 2 feet. https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/2019SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 16/25 12/21/2020 BMP T7.30: Bioretention • Bioretention areas should have a minimum shoulder of 12 inches (30.5 cm) between the road edge and beginning of the bioretention side slope where flush curbs are used. Compaction effort for the shoulder should 90 percent proctor. Ponding Area Ponding depth recommendations: • Maximum ponding depth: 12 inches (30.5 cm). • Surface pool drawdown time: 24 hours For design on projects subject to 1-3.4.5 MRS: On -Site Stormwater Management, and choosing to use The List Approach of that requirement, the bioretention BMP shall have a horizontally projected surface area below the overflow which is at least 5% of the area draining to it. The ponding area provides surface storage for storm flows, particulate settling, and the first stages of pollutant treatment within the bioretention BMP. Pool depth and draw -down rate are recommended to provide surface storage, adequate infiltration capability, and soil moisture conditions that allow for a range of appropriate plant species. Soils must be allowed to dry out periodically in order to: restore hydraulic capacity to receive flows from subsequent storms; maintain infiltration rates; maintain adequate soil oxygen levels for healthy soil biota and vegetation; provide proper soil conditions for biodegradation and retention of pollutants. Maximum designed depth of ponding (before surface overflow to a pipe or ditch) must be considered in light of drawdown time. For bioretention areas with underdrains, elevating the drain to create a temporary saturated zone beneath the drain is advised to promote denitrification (conversion of nitrate to nitrogen gas) and prolong moist soil conditions for plant survival during dry periods (see the Underdrain (optional) section below for details). Surface Overflow Surface overflow can be provided by vertical stand pipes that are connected to underdrain systems, by horizontal drainage pipes or armored overflow channels installed at the designed maximum ponding elevations. Overflow can also be provided by a curb cut at the down -gradient end of the bioretention area to direct overflows back to the street. Overflow conveyance structures are necessary for all bioretention BMPs to safely convey flows that exceed the capacity of the BMP and to protect downstream natural resources and property. The minimum freeboard from the invert of the overflow stand pipe, horizontal drainage pipe or earthen channel should be 6 inches unless otherwise specified by the local jurisdiction's design standards. Soil Depth The bioretention soil mix depth must be 18 inches to provide Runoff Treatment and good growing conditions for selected plants. Ecology does not recommend bioretention soil mix depths greater than 18 inches due to preliminary monitoring results indicating that phosphorus can leach from the bioretention soil mix. Filter Fabrics https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 17/25 12/21/2020 BMP T7.30: Bioretention Do not use filter fabrics between the subgrade and the bioretention soil mix. The gradation between existing soils and bioretention soil mix is not great enough to allow significant migration of fines into the bioretention soil mix. Additionally, filter fabrics may clog with downward migration of fines from the bioretention soil mix. Underdrain (optional). Where the underlying native soils have a measured initial Ksat between 0.3 and 0.6 inches per hour, bioretention BMPs without an underdrain, or with an elevated underdrain directed to a surface outlet, may be used to satisfy The List Approach of 1-3.4.5 MR5: On -Site Stormwater Management. Underdrained bioretention BMPs must meet the following criteria if they are used to satisfy The List Approach of 1-3.4.5 MR5: On -Site Stormwater Management: • the invert of the underdrain must be elevated 6 inches above the bottom of the aggregate bedding layer. A larger distance between the underdrain and bottom of the bedding layer is desirable, but cannot be used to trigger infeasibility due to inadequate vertical separation to the seasonal high water table, bedrock, or other impermeable layer. • the distance between the bottom of the bioretention soil mix and the crown of the underdrain pipe must be not less than 6 but not more than 12 inches; • the aggregate bedding layer must run the full length and the full width of the bottom of the bioretention BMP; • the BMP must not be underlain by a low permeability liner that prevents infiltration into the native soil. Figure V-5.13: Typical Bioretention w/Underdrain depicts a bioretention BMP with an elevated underdrain. Figure V-5.14: Typical Bioretention w/Liner (Not LID) depicts a bioretention BMP with an underdrain and a low permeability liner. The latter is not considered a low impact development BMP. It cannot be used to implement The List Approach of I-3.4.5 MR5: On -Site Stormwater Management. The volume above an underdrain pipe in a bioretention BMP provides pollutant filtering and minor detention. However, only the void volume of the aggregate below the underdrain invert and above the bottom of the bioretention BMP (subgrade) can be used in the continuous runoff model for dead storage volume that provides Flow Control benefit. Assume a 40% void volume for the Type 26 mineral aggregate specified below. Underdrain systems should only be installed when the bioretention BMP is: • Located near sensitive infrastructure (e.g., unsealed basements) and potential for flooding is likely. • Used for filtering storm flows from gas stations or other pollutant hotspots (requires impermeable liner). • Located above native soils with infiltration rates that are not adequate to meet maximum pool and system dewater rates, or are below a minimum rate allowed by the local government. The underdrain can be connected to a downstream bioretention swale, to another bioretention cell as part of a connected treatment system, daylight to a dispersion area using an effective flow dispersion practice, or to a storm drain. https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 18/25 12/21/2020 Underdrain Pipe BMP T7.30: Bioretention Underdrains shall be slotted, thick-walled plastic pipe. The slot opening should be smaller than the smallest aggregate gradation for the gravel filter bed (see Underdrain Aggregate Filter and Bedding Layer below) to prevent migration of the material into the drain. This configuration allows for pressurized water cleaning and root cutting if necessary. Underdrain pipe recommendations: • Minimum pipe diameter: 4 inches (pipe diameter will depend on hydraulic capacity required, 4 to 8 inches is common). • Slotted subsurface drain PVC per ASTM D1785 SCH 40. • Slots should be cut perpendicular to the long axis of the pipe and be 0.04 to 0.069 inches by 1 inch long and be spaced 0.25 inches apart (spaced longitudinally). Slots should be arranged in four rows spaced on 45 -degree centers and cover'/2 of the circumference of the pipe. See Underdrain Aggregate Filter and Bedding Layer (below) for aggregate gradation appropriate for this slot size. • Underdrains should be sloped at a minimum of 0.5 percent unless otherwise specified by an engineer. Perforated PVC or flexible slotted HDPE pipe cannot be cleaned with pressurized water or root cutting equipment, are less durable and are not recommended. Wrapping the underdrain pipe in filter fabric increases chances of clogging and is not recommended. A 6 -inch rigid non -perforated observation pipe or other maintenance access should be connected to the underdrain every 250 to 300 feet to provide a clean-out port, as well as an observation well to monitor dewatering rates. Underdrain Aggregate Filter and Bedding Layer Aggregate filter and bedding layers buffer the underdrain system from sediment input and clogging. When properly selected for the soil gradation, geosynthetic filter fabrics can provide adequate protection from the migration of fines. However, aggregate filter and bedding layers, with proper gradations, provide a larger surface area for protecting underdrains and are preferred. Table V-5.3: Mineral Aggregate Gradation for Underdrain Filter and Bedding Layer Sieve size Percent Passing 3/4 inch 100 '/4 inch 30-60 US No. 8 20-50 US No. 50 3-12 US No. 200 0-1 Note: The above gradation is a Type 26 mineral aggregate as detailed for gravel backfill for drains in the City of Seattle Standard Specifications for Road, Bridge, and Municipal Construction ,(Seattle Public Utilities, 2014). https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 19/25 12/21/2020 BMP T7.30: Bioretention Place the underdrain pipe on a bed of the Type 26 aggregate with a minimum thickness of 6 inches and cover with Type 26 aggregate to provide a 1 -foot minimum depth around the top and sides of the slotted pipe. See the Low Impact Development Technical Guidance Manual for Puget Sound .(Hinman and Wulkan, 2012). Orifice and Other Flow Control sStructures The minimum orifice diameter should be 0.5 inches to minimize clogging and maintenance requirements. Check Dams and Weirs Check dams are necessary for reducing flow velocity and potential erosion, as well as increasing detention time and infiltration capability on sloped sites. Typical materials include concrete, wood, rock, compacted dense soil covered with vegetation, and vegetated hedge rows. Design depends on Flow Control goals, local regulations for structures within road right-of-ways and aesthetics. Optimum spacing is determined by Flow Control benefit (modeling) in relation to cost consideration. See the Low Impact Development Technical Guidance Manual for Puget Sound .(Hinman and Wulkan, 2012) for displays of typical designs. UIC Discharge Stormwater that has passed through the bioretention soil mix may also discharge to a gravel -filled dug or drilled drain. Underground Injection Control (UIC) regulations are applicable and must be followed (Chapter 173-218 WAC). See 1-4 UIC Program. Hydraulic Restriction Layers: Adjacent roads, foundations or other infrastructure may require that infiltration pathways are restricted to prevent excessive hydrologic loading. Two types of restricting layers can be incorporated into bioretention designs: • Clay (bentonite) liners are low permeability liners. Where clay liners are used underdrain systems are necessary. See V-1.3.3 Low Permeability Liners for guidelines. • Geomembrane liners completely block infiltration to subgrade soils and are used for ground water protection when bioretention BMPs are installed to filter storm flows from pollutant hotspots or on sidewalls of bioretention areas to restrict lateral flows to roadbeds or other sensitive infrastructure. Where geomembrane liners are used to line the entire BMP, underdrain systems are necessary. See V-1.3.3 Low Permeability Liners for guidelines. Plant Materials In general, the predominant plant material utilized in bioretention areas are species adapted to stresses associated with wet and dry conditions. Soil moisture conditions will vary within the facility from saturated (bottom of cell) to relatively dry (rim of cell). Accordingly, wetland plants may be used in the lower areas, if saturated soil conditions exist for appropriate periods, and drought -tolerant species planted on the perimeter of the facility or on mounded areas. See the Low Impact Development Technical Guidance Manual for Puget Sound .(Hinman and https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/2019SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 20/25 12/21/2020 BMP T7.30: Bioretention Wulkan, 2012) for additional guidance and recommended plant species. See also City of Seattle's ROW bioretention plant lists found in Seattle's GSI Manual, Appendix G, at the following web address: https://www.seattle.gov/util/cs/groups/public/@spu/@engineering/documents/webcontent/1 079167.pdf The side slopes for the bioretention facility (vertical or sloped) can affect the plant selection and must be considered. Additionally, trees can be planted along the side slopes or bottom of bioretention cells that are unlined. Mulch Layer You can design bioretention areas with or without a mulch layer. When used, mulch shall be: • Medium compost in the bottom of the BMP (compost is less likely to float during cell inundation). Compost shall not include biosolids or manures. • Shredded or chipped hardwood or softwood on side slopes above ponding elevation and rim area. Arborist mulch is mostly woody trimmings from trees and shrubs and is a good source of mulch material. Wood chip operations are a good source for mulch material that has more control of size distribution and consistency. Do not use shredded construction wood debris or any shredded wood to which preservatives have been added. • Free of weed seeds, soil, roots and other material that is not bole or branch wood and bark. • A maximum of 2 to 3 inches thick. Mulch shall not be: • Grass clippings (decomposing grass clippings are a source of nitrogen and are not recommended for mulch in bioretention areas). • Pure bark (bark is essentially sterile and inhibits plant establishment). In bioretention areas where higher flow velocities are anticipated, an aggregate mulch may be used to dissipate flow energy and protect underlying bioretention soil mix. Aggregate mulch varies in size and type, but 1 to 1 1/2 inch gravel (rounded) decorative rock is typical. Runoff Model Representation Note that if the project is using bioretention to only meet The List Approach within 1-3.4.5 MRS: On -Site Stormwater Management, there is no need to model the bioretention in a continuous runoff model. Size the bioretention as described above in Ponding Area. The guidance below is to show compliance with the LID Performance Standard in 1-3.4.5 MR5: On -Site Stormwater Management, or the standards in 1-3.4.6 MR6: Runoff Treatment, 1-3.4.7 MR7: Flow Control, and/or 1- 3.4.8 MR8: Wetlands Protection. Continuous runoff modeling software include modeling elements for bioretention. https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 21/25 12/21/2020 BMP T7.30: Bioretention The equations used by the elements are intended to simulate the wetting and drying of soil as well as how the soils function once they are saturated. This group of LID elements uses the modified Green Ampt equation to compute the surface infiltration into the amended soil. The water then moves through the top amended soil layer at the computed rate, determined by Darcy's and Van Genuchten's equations. As the soil approaches field capacity (i.e., gravity head is greater than matric head), the model determines when water will begin to infiltrate into the second soil layer (lower layer). This occurs when the matric head is less than the gravity head in the first layer (top layer). The second layer is intended to prevent loss of the amended soil layer. As the second layer approaches field capacity, the water begins to move into the third layer — the gravel underlayer. For each layer, the user inputs the depth of the layer and the type of soil. Within the WWHM continuous runoff model, for the Ecology -recommended soil specifications for each layer in the design criteria for bioretention, the model will automatically assign pre -determined appropriate values for parameters that determine water movement through that soil. These include: wilting point, minimum hydraulic conductivity, maximum saturated hydraulic conductivity, and the Van Genuchten number. For bioretention with underlying perforated drain pipes that discharge to the surface, the only volume available for storage (and modeled as storage as explained herein) is the void space within the aggregate bedding layer below the invert of the drain pipe. Use 40% void space for the Type 26 mineral aggregate specified in Underdrain .(optional) (above). Modeling: It is preferable to enter each bioretention device and its drainage area into the approved computer models for estimating their performance. However, where site layouts involve multiple bioretention facilities, the modeling schematic can become extremely complicated or not accommodated by the available schematic grid. In those cases, multiple bioretention facilities with similar designs (i.e., soil depth, ponding depth, freeboard height, and drainage area to ponding area ratio), and infiltration rates (Ecology suggests within a factor of 2) may have their drainage areas and ponded areas be combined, and represented in the runoff model as one drainage area and one bioretention device. In this case, use a weighted average of the design infiltration rates at each location. The averages are weighted by the size of their drainage areas. For bioretention with side slopes of 3H:1 V or flatter, infiltration through the side slope areas can be significant. Where side slopes are 3H:1 V or flatter, bioretention can be modeled allowing infiltration through the side slope areas to the native soil. In WWHM, modeling of infiltration through the side slope areas is accomplished by switching the default setting for "Use Wetted Surface Area (sidewalls): from "NO" to "YES." Installation Criteria Excavation Soil compaction can lead to bioretention BMP failure; accordingly, minimizing compaction of the base and sidewalls of the bioretention area is critical. Excavation should never be allowed during wet or saturated conditions (compaction can reach depths of 2-3 feet during wet conditions and mitigation is likely to not be https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 22/25 12/21/2020 BMP T7.30: Bioretention possible). Excavation should be performed by machinery operating adjacent to the bioretention BMP, and no heavy equipment with narrow tracks, narrow tires, or large lugged, high pressure tires should be allowed on the bottom of the bioretention BMP. If machinery must operate in the bioretention area for excavation, use light weight, low ground -contact pressure equipment and rip the base at completion to refracture soil to a minimum of 12 inches. If machinery operates in the BMP footprint, subgrade infiltration rates must be field tested and compared to initial Ksat tests obtained during design. Failure to meet or exceed the initial Ksat tests will require revised engineering designs to verify achievement of Runoff Treatment and Flow Control benefits that were estimated in the Stormwater Site Plan. Prior to placement of the bioretention soil mix, the finished subgrade shall: • Be scarified to a minimum depth of 3 inches. • Have any sediment deposited from construction runoff removed. To remove all introduced sediment, subgrade soil should be removed to a depth of 3-6 inches and replaced with bioretention soil mix. • Be inspected by the responsible engineer to verify required subgrade condition. Sidewalls of the BMP, beneath the surface of the bioretention soil mix, can be vertical if soil stability is adequate. Exposed sidewalls of the completed bioretention area with bioretention soil mix in place should be no steeper than 3H:1V. The bottom of the BMP should be flat. Soil Placement On-site soil mixing or placement shall not be performed if bioretention soil mix or subgrade soil is saturated. The bioretention soil mix should be placed and graded by machinery operating adjacent to the bioretention BMP. If machinery must operate in the bioretention cell for soil placement, use light weight equipment with low ground - contact pressure. If machinery operates in the BMP footprint, subgrade infiltration rates must be field tested and compared to initial Ksat tests obtained during design. Failure to meet or exceed the initial Ksat tests will require revised engineering designs to verify achievement of Runoff Treatment and Flow Control benefits that were estimated in the Stormwater Site Plan. The soil mixture shall be placed in horizontal layers not to exceed 6 inches per lift for the entire area of the bioretention BMP. Compact the bioretention soil mix to a relative compaction of 85 percent of modified maximum dry density (ASTM D 1557). Compaction can be achieved by boot packing (simply walking over all areas of each lift), and then apply 0.2 inches (0.5 cm) of water per 1 inch (2.5 cm) of bioretention soil mix depth. Water for settling should be applied by spraying or sprinkling. Temporary Erosion and Sediment Control JESC). Controlling erosion and sediment are most difficult during clearing, grading, and construction; accordingly, minimizing site disturbance to the greatest extent practicable is the most effective sediment management. During construction: https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 23/25 12/21/2020 BMP T7.30: Bioretention • Bioretention BMPs should not be used as sediment control BMPs, and all drainage should be directed away from bioretention BMPs after initial rough grading. Flow can be directed away from the BMP with temporary diversion swales or other approved protection. If introduction of construction runoff cannot be avoided see below for guidelines. • Construction on bioretention BMPs should not begin until all contributing drainage areas are stabilized according to erosion and sediment control BMPs and to the satisfaction of the engineer. • If the design includes curb and gutter, the curb cuts and inlets should be blocked until bioretention soil mix and mulch have been placed and planting completed (when possible), and dispersion pads are in place. Every effort during design, construction sequencing and construction should be made to prevent sediment from entering bioretention BMPs. However, bioretention areas are often distributed throughout the project area and can present unique challenges during construction. See the Low Impact Development Technical Guidance Manual for Puget Sound .(Hinman and Wulkan, 2012) for guidelines if no other options exist and runoff during construction must be directed through the bioretention BMPs. Erosion and sediment control practices must be inspected and maintained on a regular basis. Verification If using the default bioretention soil mix, pre -placement laboratory analysis for saturated hydraulic conductivity of the bioretention soil mix is not required. Verification of the mineral aggregate gradation, compliance with the compost specifications, and the mix ratio must be provided. If using a custom bioretention soil mix, verification of compliance with the minimum design criteria cited above for such custom mixes must be provided. This will require laboratory testing of the material that will be used in the installation. Testing shall be performed by a Seal of Testing Assurance, AASHTO, ASTM or other standards organization accredited laboratory with current and maintained certification. Samples for testing must be supplied from the bioretention soil mix that will be placed in the bioretention areas. If testing infiltration rates is necessary for post -construction verification, use the Pilot Infiltration Test (PIT) method or a double ring infiltrometer test (or other small-scale testing allowed by the local government with jurisdiction). If using the PIT method, do not excavate the bioretention soil mix (conduct the test at the elevation of the finished bioretention soil mix), use a maximum of 6 inch ponding depth and conduct the test before plants are installed. Maintenance Bioretention areas require annual plant, soil, and mulch layer maintenance to ensure optimum infiltration, storage, and pollutant removal capabilities. In general, bioretention maintenance requirements are typical landscape care procedures and include: • Watering: Plants should be selected to be drought tolerant and not require watering after establishment (2 to 3 years). Watering may be required during prolonged dry periods after plants are established. • Erosion control: Inspect flow entrances, ponding area, and surface overflow areas periodically, and replace soil, plant material, and/or mulch layer in areas if erosion has occurred. Properly designed BMPs with https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/2019SWM M WW/2019SWMMW W.htm#Topics/VolumeV/I nfiltrationBMPs/BM Pt730. htm%3FToc... 24/25 12/21/2020 BMP T7.30: Bioretention appropriate flow velocities should not have erosion problems except perhaps in extreme events. If erosion problems occur, the following should be reassessed: (1) flow volumes from contributing areas and bioretention cell sizing; (2) flow velocities and gradients within the cell; and (3) flow dissipation and erosion protection strategies in the pretreatment area and flow entrance. If sediment is deposited in the bioretention area, immediately determine the source within the contributing area, stabilize, and remove excess surface deposits. • Sediment removal: Follow the maintenance plan schedule for visual inspection and remove sediment if the volume of the ponding area has been compromised. • Plant material: Depending on aesthetic requirements, occasional pruning and removing dead plant material may be necessary. Replace all dead plants and if specific plants have a high mortality rate, assess the cause and replace with appropriate species. Periodic weeding is necessary until plants are established. • Weeding: Invasive or nuisance plants should be removed regularly and not allowed to accumulate and exclude planted species. At a minimum, schedule weeding with inspections to coincide with important horticultural cycles (e.g., prior to major weed varieties dispersing seeds). Weeding should be done manually and without herbicide applications. The weeding schedule should become less frequent if the appropriate plant species and planting density are used and the selected plants grow to capture the site and exclude undesirable weeds. • Nutrient and pesticides: The soil mix and plants are selected for optimum fertility, plant establishment, and growth. Nutrient and pesticide inputs should not be required and may degrade the pollutant processing capability of the bioretention area, as well as contribute pollutant loads to receiving waters. By design, bioretention BMPs are located in areas where phosphorous and nitrogen levels may be elevated and these should not be limiting nutrients. If in question, have soil analyzed for fertility. • Mulch: Replace mulch annually in bioretention BMPs where heavy metal deposition is high (e.g., contributing areas that include gas stations, ports and roads with high traffic loads). In residential settings or other areas where metals or other pollutant loads are not anticipated to be high, replace or add mulch as needed (likely 3 to 5 years) to maintain a 2 to 3 inch depth. • Soil: Soil mixes for bioretention BMPs are designed to maintain long-term fertility and pollutant processing capability. Estimates from metal attenuation research suggest that metal accumulation should not present an environmental concern for at least 20 years in bioretention systems, but this will vary according to pollutant load. Replacing mulch media in bioretention BMPs where heavy metal deposition is likely provides an additional level of protection for prolonged performance. If in question, have soil analyzed for fertility and pollutant levels. Refer to Appendix V-A: BMP Maintenance Tables for additional maintenance guidelines. Washington State Department of Ecology 2019 Stormwater Management Manual for Western Washington (2019 SWMMWW) Publication No.19-10-021 https://fortress.wa.gov/ecy/ershare/wq/Permits/Flare/20l 9SWMMWW/2019SWMMWW.htm#Topics/VolumeV/infiltrationBMPs/BMPt730.htm%3FToc... 25/25 Edge of pavement or curb -cut 2" woodchip mulch or aggregate Provide a 1" drop from the edge of pavement Overflow structure or flow path Notes: 1. Scarify subgrade 3" min. before bioretention soil installation 2. Compact BSM to 85% per ASTM 1577 DEPARTMENT OF ECOLOGY State of Washington BSM bottom width varies, V minimum Ponding depth Provide a 1" drop from the edge of sidewalk 1� / 6" min. freeboard Minimum separation varies, see design guidance Sidewalk LI- 11 I I I I—Irl� 2" woodchip mulch or aggregate 3" coarse compost in ponding area 18" Bioretention Soil Mix (BSM) Seasonal high water table, bedrock, or other impervious layer Typical Bioretention NOT TO SCALE Revised January 2019 Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. Edge of pavement or curb -cut 2" woodchip mulch or aggregate Provide a 1" drop from the edge of pavement Overflow structure or flow path 6" to 12" (see note 3) BSM bottom width varies, 1' minimum Ponding depth ��varies Provide a 1" drop from the edge of sidewalk 6" min. freeboard 6" (see note 4) Mineral aggregate bottom width to match BSM bottom width Sidewalk III 2" woodchip mulch or aggregate 3" coarse compost in ponding area 18" Bioretention Soil Mix (BSM) Mineral aggregate Underdrain pipe Notes: 1. Scarify subgrade 3" min. before BSM installation 2. Compact BSM to 85% per ASTM 1577 3. Minimum 6" to discourage fines from entering the underdrain from the BSM. Maximum 12" to prevent unnecessary BMP depth from encroaching into the seasonal high ground water. 4. If depth to the seasonal high ground water allows, this distance may be larger. 5. When an underdrain is used, the design must ensure that the seasonal high ground water does not encroach into the BMP (including the mineral aggregate layer surrounding the underdrain pipe). waa Nno" DEPARTMENT OF ECOLOGY State of Washington NOT TO SCALE Typical Bioretention w/Underdrain Revised January 2019 Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. Provide a 1" drop from the edge of pavement Provide a 1" drop from the edge of sidewalk Notes: 1. Scarify subgrade 3" min. before bioretention soil installation 2. Compact BSM to 85% per ASTM 1577 DEPARTMENT OF ECOLOGY State of Washington NOT TO SCALE Typical Bioretention w/Liner (Not LID) Revised January 2019 Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer. gutter 6" Plan View NOT TO SCALE MINr DEPARTMENT OF ECOLOGY State of Washington DESIGNER INFORMATION: 1. 3 o N > d - `�►subgradei a �d a ° 4" not driane aCh ($e d ;h for sidewalk 2. a hannel & grate10 seenote 2) Bioretention each facility. Provide stations and/or •V dimensions and elevations at every inlet, W W W W W W ;ck dam sidewalk notch. note 2) 3. Longitudinal slope of planter matches road. W W CU W EL W W Sidewalk elevation must be set above inlet and outlet elevations to allow overflow to a� � U) drain to street before sidewalk. a Minimum interior planter width is 3 feet. A a d 4" thick i splash p a 4 o a ° Concre d � ° a a a a e d a a D d a G Q d C Sidewalk W W W W W W W W W W W W W W W 6. Existing utility lines must be sleeved or a relocated. Proposed utility lines to be located out of the facility. 7. m in fetal inlet '-0" ty . d 3 o c 3d at inlet constraints. 8. May use concrete or pavers. %=I W W W W W W W W W W W �'-R" Curb u. 3'-0' min. I I gutter 6" Plan View NOT TO SCALE MINr DEPARTMENT OF ECOLOGY State of Washington DESIGNER INFORMATION: 1. Adapt plan view example to your `�►subgradei engineered design. ;h for sidewalk 2. Include beginning and ending stations for Bioretention each facility. Provide stations and/or ge, as necessary dimensions and elevations at every inlet, outlet, check dam, planter corner and ;ck dam sidewalk notch. note 2) 3. Longitudinal slope of planter matches road. 4. Sidewalk elevation must be set above inlet and outlet elevations to allow overflow to \ drain to street before sidewalk. 5. Minimum interior planter width is 3 feet. A minimum of 4 feet interior planter width is required for street trees in planter. 6. Existing utility lines must be sleeved or relocated. Proposed utility lines to be located out of the facility. 7. Area and depth of facility are based upon :oncrete engineering calculations and right-of-way 3d at inlet constraints. 8. May use concrete or pavers. e or pavers 6., Concrete or pavers (to be specified by ---- designer) a Curb and gutter (by others) Finished - grade of planter +-d- 2'-6" y - Existing `�►subgradei Bioretention Soil Mix Open graded aggregate (when required) Sidewalk drainage notch to be 1" lower Top of wall at than sidewalk, end of planter sloped to facility 4" min. exposed 12" max T wall a Planter wall 6" benchfor • Section 1 1 construction Example of a Bioretention Planter Revised October 2016 Please see http://www.ecy.wa.gov/copyright.html for copyright notice including permissions, limitation of liability, and disclaimer.