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2020.0106.CI0005 Storm Report (Approved) 7.29.2020FINAL STORM DRAINAGE AND EROSIOI{ &SEDIMENTATIOI{ COI{TROL REPORTFORWyndstoneYelm, \MashingtonRevised: Jun e 2020March 2020Prepared for:C&EDevelopments,LLCPO Box 2983Yelm, WA 98597Prepared by:lzbDaniel P. Smith, PEo Project ManagerApproved By:Craig Deaver, PrincipalREPORT #06164.0"l hereby state that this Drainage and Erosion/Sediment Control Plan for'Wvndstone has beenprepared by me or under my supervision and meets the standard of care and expertise which isusual and customary in this community of professional engineers. I understand that City ofYelm does not and will not assume liability for the sufTciency. suitability or performance ofdrainage facilities prepared by me."This analysis is based on data and records either supplied to, or obtained by, C.E.S. NW, Inc.These documents are referenced within the text of the analysis. The analysis has been preparedutilizing procedures and practices within the standard accepted practices of the industry.ûl.I0\ \t TABLE OF CONTENTS PAGE STORM DRAINAGE .................................................................................................................................................. 1  1. PROJECT OVERVIEW ........................................................................................................................................... 1  2. EXISTING CONDITIONS SUMMARY ...................................................................................................................... 3  3. OFFSITE ANALYSIS ............................................................................................................................................. 4  4. PERMANENT STORMWATER CONTROL PLANS .................................................................................................... 4  5. SPECIAL REPORTS AND STUDIES ........................................................................................................................ 7  6. OTHER PERMITS ................................................................................................................................................. 7  EROSION CONTROL ................................................................................................................................................ 8  7. CONSTRUCTION STORMWATER POLLUTION PREVENTION PLAN ......................................................................... 8  Appendix A General Exhibits Vicinity Map .........................................................................................................................A-1 Soils Map ..............................................................................................................................A-2 Appendix B Basin Exhibits Pre-Developed Basin Map, 11 x 17” .....................................................................................B-1 Post Developed Basin Map, 11 x 17” ...................................................................................B-2 FIRM Panel 53067C0353E ...................................................................................................B-3 Appendix C Storm Water Calculations WWHM Calculations ............................................................................................................C-1 AutoDesk Conveyance Calculations .....................................................................................C-2 FloGard Perk Filter GULD ...................................................................................................C-3 Appendix D Geotechnical Engineer’s Reports .......................................................................................D-1 Appendix E Temporary Sediment Pond Calculations ..........................................................................E-1 Appendix F Operations and Maintenance Manual ...............................................................................F-1 P:\06164.2\2019\Reports\Storm Analysis\Final Storm Report.doc 1 STORM DRAINAGE 1. Project Overview This report accompanies the final engineering plans for the Wyndstone project as submitted to the City of Yelm for site plan review. Pursuant to City of Yelm Municipal Code (YMC) 13.16.060 the methodology and design criteria for the project are established by the Department of Ecology’s 2014 Stormwater Management Manual (Manual). Project information and the analysis used for sizing of the stormwater facilities as provided to the City are included within. The Wyndstone project consists of 75 multifamily units across four building situated on parcel # 21724420300 totaling approximately 4.67 acres. The proposed project is made up of a rectangular shaped parcel of land located at the intersection of Tahoma Blvd and Durant Street, Yelm, Washington. The site is currently surrounded by Tahoma Blvd to the north, single family homes and Durant Street to the west, and vacant parcels to the south and east. A vicinity map is provided in Appendix “A” for reference. Land Use Application – Site Plan Review Address – 15025 Tahoma Blvd SE Yelm, WA 98597 Parcel Numbers – 21724420300 Zoning – R16-High Density Legal Description – Parcel No. 21724420300; 15025 Tahoma Blvd. SE parcel a of City of Yelm boundary line adjustment no. BLA 140153 YL as recorded July 18, 2014 under Auditor's File No. 4400621. In Thurston County, Washington. The Wyndstone project is proposed to be constructed in two separate phases with Buildings 1 and 2 and the site improvements constructed in Phase I, and Buildings 3 and 4 and utility connects constructed in Phase II. A new public roadway extension from Tahoma Blvd SE is proposed as part of Phase I and will extend the full length of the eastern boundary line. An infiltration trench is proposed to fully infiltrate runoff from both phases with a FloGard Perk Filter vault upstream that provides basic runoff treatment. Both facilities are sized with the WWHM modeling program and are proposed north of Building 1 and are constructed as part of Phase I. Improvements to Durant St SE are not infiltrated by the onsite stormwater P:\06164.2\2019\Reports\Storm Analysis\Final Storm Report.doc 2 improvements and is modelled as a bypass basin. Detailed facility sizing calculations and performance standard analysis are provided in Section 4 of this report. The project proposes more than 5,000 sq.ft. of new effective impervious surfaces; therefore, according to Figure 2.4.1 from Volume I of the Manual the project must meet all minimum requirements. The following is a discussion of each minimum requirement: Minimum Requirement #1: Preparation of Stormwater Site Plans: The stormwater site plan has been prepared and is summarized within this drainage report. Minimum Requirement #2: Construction Stormwater Pollution Prevention: An erosion control report that addresses SWPPP elements 1-13 is included in Section 7 and in a . Minimum Requirement #3: Source Control of Pollution: A Source Control manual will be included as part of the Operations and Maintenance Manual included in Appendix “F”. Minimum Requirement #4: Preservation of Natural Drainage Systems and Outfalls: The site is tributary to a single threshold discharge area that flows into Tahoma Blvd SE’s stormwater system and the groundwater table. Runoff in Tahoma Blvd SE is tributary to an infiltration gallery located approximately 300-feet east of the site along the south side of the roadway. A detailed downstream analysis is provided in Section 3 of this report. Minimum Requirement #5: Onsite Stormwater Management: The project fully infiltrates its runoff with an infiltration trench. Runoff that is fully infiltrated exceeds the LID Performance Standard; therefore, onsite stormwater management BMPs are not necessary except for soil amendments. All new landscaped areas are to apply soil amendments per BMP T51.3 as described on the final engineering plans. Minimum Requirement #6: Runoff Treatment: This project proposes more than 5,000 square feet of pollution generating surfaces; therefore, minimum requirement #6 is applicable to this project. A FloGard Perk Filter vault provides basic runoff treatment upstream of the infiltration trench. Sizing calculations are provided in Section 4 of this report. Minimum Requirement #7: Flow Control: The project discharges to a single threshold discharge area and exceeds flow control thresholds; therefore, an infiltration trench is proposed to fully infiltrate the runoff from both phases. Facility sizing calculations are provided in Section 4 of this report. Minimum Requirement #8: Wetland Protection: This requirement is not applicable to this project since there are no existing wetlands onsite or adjacent to the site. P:\06164.2\2019\Reports\Storm Analysis\Final Storm Report.doc 3 Minimum Requirement #9: Operation and Maintenance: The Operations and Maintenance Manual is included in Appendix “F” of this report. Optional Guidance #1: Financial Liability: The project will provide the City with all required construction financial guarantees prior to permit issuance and maintenance guarantees after construction is complete. An engineer’s estimate is to be submitted as a separate document. Optional Guidance #2: Offsite Analysis and Mitigation: The project site exists within Nisqually River Basin (WRIA 11). Runoff from the proposed improvements will be fully infiltrated with the proposed infiltration trench; therefore, downstream concerns are mitigated. A qualitative offsite analysis is provided in Section 3 of this report. 2. Existing Conditions Summary The proposed project is comprised of one 4.67-acre parcel that is predominantly pasture and brush with several scattered trees. Durant Street SE, an existing roadway, runs along the west boundary of the site. The site is relatively flat sloping north towards Tahoma Blvd SE with slopes between 2 – 10%. According to the Soil Survey of Thurston County, Washington, prepared by the United States Department of Agriculture, the site’s soils is composed of Nisqually loamy fine sand (74) and Spanaway gravelly sandy loam (110 & 111), which are a Type A soils having low erosion potential, and high infiltration potential. A description of these soils and a copy of the soil map for this project site is included within Appendix “A”. A geotechnical engineer’s report and subsequent memo, dated July 12, 2019 and July 26, 2019 respectively, has been prepared by Insight Geologic Inc. In the July 12th report they discovered that the site is underline by recessional outwash sands and gravels to the bottom of the monitoring well (MW-1) at a depth of 31.5-feet. Infiltration testing was performed and discussed in their July 26th memo which provides a design infiltration rate of 31 inches per hour at the proposed location for the infiltration trench. This rate was determined using a Large-Scale Pilot Infiltration Test. A copy of their report and memo is provided in Appendix “D”. According to FIRM Panel 53067C0353E the site is located within Zone X. This zone is considered outside of a known flood plain. A copy of the FIRM Panel 53067C0353E can be found within Appendix “B”. P:\06164.2\2019\Reports\Storm Analysis\Final Storm Report.doc 4 3. Offsite Analysis The site mitigates its runoff with an infiltration trench located on the north side of proposed Building 1. The trench fully infiltrates runoff from the site improvements to the groundwater table up to the 100-year stormwater event as modeled by the WWHM computer program. The site has little to no runoff from offsite properties. In the case of an overflow event runoff will discharge to the public closed conveyance system in Tahoma Blvd SE. Once in this system it continues east within the public conveyance system for approximately 300-feet where it is infiltrated in a 5-foot deep rock infiltration gallery along the south side of Tahoma Blvd. SE. This is the conclusion of the offsite drainage path. A downstream drainage map is included in Appendix “B”. 4. Permanent Stormwater Control Plans Existing Site Hydrology Approximately 4.345-acres of the existing site is being developed as part of the Wyndstone project. The existing site coverage includes 0.164-acres of pavement along Durant St SE and the remaining 4.181-acres is pasture. The existing site hydrology is analyzed for the purpose of determining flow control thresholds. The existing site’s flow frequencies are summarized below: 2-year 0.082-cfs 10-year 0.140-cfs 50-year 0.203-cfs 100-year 0.234-cfs A Pre-developed Drainage Basin map is included in Appendix “B”. Developed Site Hydrology The Wyndstone project will constructed four multi-family building, parking lots and associated utilities between two phases. Durant St SE will be realigned along the project’s western boundary line and a new public roadway will be constructed along the eastern boundary line. Runoff from both phases and the new public roadway is controlled with a 15-foot wide by 200- P:\06164.2\2019\Reports\Storm Analysis\Final Storm Report.doc 5 foot long by 4.5-foot deep infiltration trench located north of Building 1. A FloGard Perk Filter treatment device is upstream of the infiltration trench which provides basic runoff treatment. Durant St SE is tributary to Tahoma Blvd SE and is considered a bypass basin which does not exceed flow control thresholds. The post developed drainage basins are summarized Table 4.1 below: Sub-Basin Land-use WWHM Description Area (acre) Onsite A Yards, Landscaping, Planters A, Lawn, Flat 0.652 Onsite B Streets, Sidewalks, and Parking Lot Roads, Mod 1.847 Onsite C Roof Tops Roof Tops, Flat 1.470 Bypass A Streets and Sidewalks (Durant Street SE/Intersection Road A and Tahoma Blvd SE) Roads, Flat 0.113 Bypass B Landscaping A, Lawn, Mod 0.324 Total 4.406 Table 4.1 – Post Developed Basin Summary The flow frequencies of the onsite basins tributary to the infiltration trench are summarized below: 2-year 1.164-cfs 10-year 1.872-cfs 50-year 2.566-cfs 100-year 2.883-cfs The flow frequencies of the bypass basins are summarized below: 2-year 0.044-cfs 10-year 0.083-cfs 50-year 0.130-cfs 100-year 0.153-cfs Each basin is depicted on the Post Developed Drainage basin map included in Appendix “B”. Facility Sizing P:\06164.2\2019\Reports\Storm Analysis\Final Storm Report.doc 6 Runoff from the onsite basin is controlled with a 15-foot wide by 200-foot long by 4.5-foot deep infiltration trench with two twelve-inch dispersal pipes. A FloGard Perk Filter is sized to provide basic runoff treatment upstream of the trench. The bypass basin areas are tributary to the existing public drainage system in Tahoma Blvd SE. Flow Control As calculated by the WWHM computer program the infiltration trench is sized to fully infiltrate runoff from the site through the 100-year storm event. The trench is modeled as a trap pond to determine the required storage. According to the model the trench requires 3,570 cubic-feet of storage while 3,629 cubic-feet is provided. Vtrench = (170-feet * 4.5-feet * 15-feet – Vpipe)*n + Vpipe Vpipe = 2*L*πr2 = 2*170-feet*(0.5’)2 = 267-cf n = drain rock void ratio = 0.30 L = length of pipe = 170-feet r = 0.5-feet Vpipe = 2*170-feet*(0.5’)2 = 267 cubic-feet Vtrench = (170-feet * 4.5-feet * 15-feet – 267-cf)*0.30 + 267-cf = 3,629 cubic-feet provided. WWHM computer results are provided in Appendix “C”. The bypass area flows towards Tahoma Blvd SE downstream of the onsite improvements and infiltration trench. The bypass area includes portions of the intersection of the new roadway and Tahoma Blvd SE, the realignment of Durant Street SE and some landscape areas along Tahoma Blvd SE. These areas are analyzed to demonstrate that they do not exceed flow control thresholds from minimum requirement #7. The bypass basin includes 6,360 sq.ft. of impervious area, 0.26-acres of new landscaped areas, and a decrease of the 100-year storm event by 0.02-cfs; therefore, flow control is not necessary. WWHM computational results are provided in Appendix “C”. Water Quality An 8-foot by 9-foot FloGard Perk Filter vault is sized to provide basic runoff treatment upstream of the infiltration trench. The Department of Ecology (EYC) has provided a General Use Level Designation (GULD) with a treatment flow rate of 6.8 gpm/cartridge for a 12-inch cartridge and 10.2 gpm/cartridge for an 18-inch cartridge. According to the GULD Perk Filters are sized with P:\06164.2\2019\Reports\Storm Analysis\Final Storm Report.doc 7 the off-line water quality flow rate as calculated by the WWHM computer program (0.291-cfs). Copies of the GULD and of the WWHM results are provided in Appendix “C”. The vault treats runoff with eight (8) 12-inch and 18-inch filter stacks. Each stack provides a combined treatment flow rate of 17 gpm/stack. The required number of stacks is calculated as follows: Nstack = 449[gpm/cfs]*Qtreat[cfs]/17[gpm/stack] = 449[gpm/cfs]*0.291[cfs]/17[gpm/stack] = 7.7 stacks; therefore, use 8 stacks. Conveyance Calculations The project collect runoff with the use of catch basins within the proposed parking lot and roadway as part of a closed conveyance network. Capacity within this network is verified by routing the 25-year storm event from the developed condition through the project’s minimum pipe diameter and slope. The 25-year storm event is 2.26-cfs as determined with the WWHM computer program. The shallowest pipe proposed as part of the project is a 12” ADS N-12 pipe sloped at a half of a percent (0.5%). Using AutoDesks Manning’s Calculator it is determined that this pipe would be 74% full; therefore, the proposed conveyance system has sufficient capacity to convey the runoff from the developed site. Computer print outs are provided in Appendix “C”. 5. Special Reports and Studies A geotechnical engineer’s report and subsequent memo, dated July 12, 2019 and July 26, 2019 respectively, has been prepared by Insight Geologic Inc. Copies of the report and memo are included in Appendix “D”. 6. Other Permits Other permits are required including:  Site development and clear and grading permits;  Sanitary sewer permit;  Water main extension and DEA. P:\06164.2\2019\Reports\Storm Analysis\Final Storm Report.doc 8 EROSION CONTROL 7. Construction Stormwater Pollution Prevention Plan The minimum requirements for erosion and sediment control are defined Volume II of the Manual. The Temporary Erosion and Sediment Control Plan provides the design and locations of BMPs to control erosion and sediment. A full construction stormwater pollution prevention plan is provided as a separate document. Volume II outlines 13 Erosion and Sediment Control requirements which are summarized below: Requirement No. 1: Preserve Vegetation/Mark Clearing Limits - The project proposes to clear areas onsite. Clearing limits are to be staked by a professional land surveyor as shown on the approved plans. Clearing shall remain within these limits. Requirement No. 2: Establish Construction Access - A construction entrance (BMP C105) is proposed to protect Tahoma Blvd SE from sediment. Adjacent paved surfaces must be cleaned daily, or if deemed necessary, more frequently. Requirement No. 3: Control Flow Rates - The project will clear approximately 4.67 acres to construct the site improvements. The project will mitigate runoff with cover measures (BMP C120 and C121), silt fences (BMP C233) interceptor swales (BMP C200), check dams (BMP C207), and a temporary sediment pond (BMP C241). Temporary sediment pond sizing calculations are included in Appendix “E”. Requirement No. 4: Install Sediment Controls - The project proposes silt fences (BMP C233) and interceptor swales (BMP C200) around the perimeter of the site and a temporary sediment pond to trap sediment onsite. Requirement No. 5: Stabilize Soils - The project will stabilize exposed soils with the use of cover measures. These cover measures are mulching, temporary seeding, and plastic sheeting (BMP C120, C121, C123). Requirement No.6: Protect Slopes - Just like stabilizing the exposed soils the project’s exposed slopes will be controlled with the same covering measures (BMP C120, C121, and BMP C123). Requirement No. 7: Protect Drain Inlets - Existing offsite drain inlets and proposed drain inlets will be protected from sediment with the use of bag filters (BMP C220). Requirement No. 8: Stabilization of Channels and Outlets - There are no proposed or exiting channels and outlets that need protection onsite or offsite. Requirement No. 9: Control Pollutants - The project will require earth moving equipment. When vehicles are stored onsite care needs to be taken to make sure that any fluid leaks are P:\06164.2\2019\Reports\Storm Analysis\Final Storm Report.doc 9 contained with drip pans and the fluids are disposed of properly. All spills need to be cleaned up immediately as per the Department of Ecology (EYC) and City of Yelm Standards. Requirement No. 10: Control Dewatering - This project proposal includes dewatering with the use of a temporary sediment pond (BMP C241). Runoff and seepage should be collected and conveyed to the temporary sediment pond for sediment removal. Water should be collected and conveyed with the use of interceptor swales (BMP C200) or by pumping directly to the temporary sediment pond. Requirement No. 11: Maintain BMPs - The proposed BMPs need to be maintained as per the approved plans notes and specifications. In general, when sediment accumulation has reached 1/3 of the treatment device or one (1) foot of depth it should be removed. Also, if there is a major storm event then the proposed BMPs should be checked and cleaned appropriately. If the sediment removed from these devices is approved by a geotechnical engineer, they can be stabilized onsite. If not, they must be removed as per the EYC and the City’s requirements. Requirement No. 12: Manage the Project - A construction sequence is provided on the plans. This construction sequence needs to be followed to ensure that sediment is not deposited downstream. The City and the Project Engineer needs to inspect the erosion control BMPs after installation and during construction. The contractor is to employ a Certified Erosion and Sediment Control Lead (CESL, BMP C160) as described by the State to help manage and inspect the erosion control devices. Detailed descriptions of each BMP listed above can be found in Volume 2 of the Stormwater Management Manual for Western Washington, 2014. Requirement No. 13: Manage the Project - LID BMPs such as soil amendments and an infiltration trench are proposed as part of this project. The areas subject to soil amendments and infiltration trench should not be re-compacted during construction of each building to protect these BMPs APPENDIX A General Exhibits Vicinity Map A-1 Soils Map and Description A-2 Soil Map—Thurston County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/13/2019 Page 1 of 351989405198960519898051990005199020519904051990605199080519910051991205199140519894051989605198980519900051990205199040519906051990805199100519912051991405199160528720528740528760528780528800528820528840528860528880 528720 528740 528760 528780 528800 528820 528840 528860 528880 46° 56' 43'' N 122° 37' 21'' W46° 56' 43'' N122° 37' 13'' W46° 56' 35'' N 122° 37' 21'' W46° 56' 35'' N 122° 37' 13'' WN Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS84 0 50 100 200 300 Feet 0 15 30 60 90 Meters Map Scale: 1:1,090 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 13, Sep 16, 2019 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 11/13/2019 Page 2 of 3 Map Unit Legend Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 74 Nisqually loamy fine sand, 3 to 15 percent slopes 0.7 15.1% 110 Spanaway gravelly sandy loam, 0 to 3 percent slopes 3.3 75.3% 111 Spanaway gravelly sandy loam, 3 to 15 percent slopes 0.4 9.5% Totals for Area of Interest 4.4 100.0% Soil Map—Thurston County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 11/13/2019 Page 3 of 3 APPENDIX B Basin Exhibits Pre-developed Basin Map, 11 x 17” B-1 Developed Basin Map, 11 x 17” B-2 FIRM Panel 53067C0353E B-3 Downstream Analysis Map B-4 AREA OF MINIMAL FLOOD HAZARD Zone XT17N R1E S24 CITY OF YELM530310 USGS The National Map: Orthoimagery. Data refreshed April, 2019. National Flood Hazard Layer FIRMette 0 500 1,000 1,500 2,000250Feet Ü122°37'35.01"W 46°56'49.68"N 122°36'57.56"W 46°56'25.12"N SEE FIS REPORT FOR DETAILED LEGEND AND INDEX MAP FOR FIRM PANEL LAYOUT SPECIAL FLOODHAZARD AR EAS Without Base Flood Elevation (BFE)Zone A, V, A99With BFE or Depth Zone AE, AO, AH, VE, AR Regulator y Floodway 0.2% Annual Chance Flood Hazard, Areasof 1% annual chance flood with averagedepth less than one foot or with drainageareas of less than one square mile Zone X Future Conditions 1% AnnualChance Flood Hazard Zone XArea with Reduced Flood Risk due toLevee. See Notes.Zone X Area with Flood Risk due to Levee Zone D NO SCREE N Area of Minimal Flood Hazard Zone X Area of Undetermined Flood Hazard Zone D Channel, Culver t, or Storm SewerLevee, Dike, or Floodwall Cross Sections with 1% Annual Chance17.5 Water Surface ElevationCoastal Transect Coastal Transect BaselineProfile BaselineHydrographic Feature Base Flood Elevation Line (BFE) Effective LOMRs Limit of StudyJurisdiction Boundar y Digital Data Available No Digital Data Available Unmapped This map complies with FEMA's standards for the use of digital flood maps if it is not void as described below. The basemap shown complies with FEMA's basemap accuracy standards The flood hazard information is derived directly from theauthoritative NFHL web ser vices provided by FEMA. This mapwas exported on 11/13/2019 at 11:36:26 PM and does notreflect changes or amendments subsequent to this date andtime. The NFHL and effective information may change orbecome superseded by new data over time. This map image is void if the one or more of the following mapelements do not appear: basemap imagery, flood zone labels,legend, scale bar, map creation date, community identifiers,FIRM panel number, and FIRM effective date. Map images forunmapped and unmodernized areas cannot be used forregulatory purposes. Legend OTHER AREAS OFFLOOD HAZARD OTHER AREAS GENERALSTRUCTURES OTHERFEATURES MAP PANELS 8 1:6,000 B 20.2 The pin displayed on the map is an approximate point selected by the user and does not represent an authoritative proper ty location. APPENDIX C Storm Water Calculations WWHM Calculations C-1 AutoDesk Conveyance Calculations C-2 FloGard Perk Filter GULD C-3 WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: 06164.2 Site Name: Wynstone Site Address: City : Yelm, WA Report Date: 3/3/2020 Gage : Eaton Creek Data Start : 1955/10/01 Data End : 2011/09/30 Precip Scale: 0.86 Version Date: 2019/09/13 Version : 4.2.17 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre A B, Pasture, Flat 4.181 Pervious Total 4.181 Impervious Land Use acre ROADS FLAT 0.225 Impervious Total 0.225 Basin Total 4.406 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre A B, Lawn, Flat .652 Pervious Total 0.652 Impervious Land Use acre ROADS FLAT 1.847 ROOF TOPS FLAT 1.47 Impervious Total 3.317 Basin Total 3.969 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater Trapezoidal Pond 1 Trapezoidal Pond 1 ___________________________________________________________________ Name : Trapezoidal Pond 1 Bottom Length: 170.00 ft. Bottom Width: 15.00 ft. Depth: 4.5 ft. Volume at riser head: 0.0820 acre-feet. Infiltration On Infiltration rate: 30 Infiltration safety factor: 1 Total Volume Infiltrated (ac-ft.): 518.798 Total Volume Through Riser (ac-ft.): 0 Total Volume Through Facility (ac-ft.): 518.798 Percent Infiltrated: 100 Total Precip Applied to Facility: 0 Total Evap From Facility: 0 Side slope 1: 0 To 1 Side slope 2: 0 To 1 Side slope 3: 0 To 1 Side slope 4: 0 To 1 Discharge Structure Riser Height: 1.4 ft. Riser Diameter: 18 in. Element Flows To: Outlet 1 Outlet 2 ___________________________________________________________________ Pond Hydraulic Table Stage(feet) Area(ac.) Volume(ac-ft.) Discharge(cfs) Infilt(cfs) 0.0000 0.058 0.000 0.000 0.000 0.0500 0.058 0.002 0.000 1.770 0.1000 0.058 0.005 0.000 1.770 0.1500 0.058 0.008 0.000 1.770 0.2000 0.058 0.011 0.000 1.770 0.2500 0.058 0.014 0.000 1.770 0.3000 0.058 0.017 0.000 1.770 0.3500 0.058 0.020 0.000 1.770 0.4000 0.058 0.023 0.000 1.770 0.4500 0.058 0.026 0.000 1.770 0.5000 0.058 0.029 0.000 1.770 0.5500 0.058 0.032 0.000 1.770 0.6000 0.058 0.035 0.000 1.770 0.6500 0.058 0.038 0.000 1.770 0.7000 0.058 0.041 0.000 1.770 0.7500 0.058 0.043 0.000 1.770 0.8000 0.058 0.046 0.000 1.770 0.8500 0.058 0.049 0.000 1.770 0.9000 0.058 0.052 0.000 1.770 0.9500 0.058 0.055 0.000 1.770 1.0000 0.058 0.058 0.000 1.770 1.0500 0.058 0.061 0.000 1.770 1.1000 0.058 0.064 0.000 1.770 1.1500 0.058 0.067 0.000 1.770 1.2000 0.058 0.070 0.000 1.770 1.2500 0.058 0.073 0.000 1.770 1.3000 0.058 0.076 0.000 1.770 1.3500 0.058 0.079 0.000 1.770 1.4000 0.058 0.082 0.000 1.770 1.4500 0.058 0.084 0.177 1.770 1.5000 0.058 0.087 0.502 1.770 1.5500 0.058 0.090 0.919 1.770 1.6000 0.058 0.093 1.404 1.770 1.6500 0.058 0.096 1.938 1.770 1.7000 0.058 0.099 2.501 1.770 1.7500 0.058 0.102 3.072 1.770 1.8000 0.058 0.105 3.632 1.770 1.8500 0.058 0.108 4.160 1.770 1.9000 0.058 0.111 4.639 1.770 1.9500 0.058 0.114 5.055 1.770 2.0000 0.058 0.117 5.401 1.770 2.0500 0.058 0.120 5.676 1.770 2.1000 0.058 0.122 5.892 1.770 2.1500 0.058 0.125 6.137 1.770 2.2000 0.058 0.128 6.338 1.770 2.2500 0.058 0.131 6.533 1.770 2.3000 0.058 0.134 6.723 1.770 2.3500 0.058 0.137 6.907 1.770 2.4000 0.058 0.140 7.086 1.770 2.4500 0.058 0.143 7.261 1.770 2.5000 0.058 0.146 7.432 1.770 2.5500 0.058 0.149 7.599 1.770 2.6000 0.058 0.152 7.763 1.770 2.6500 0.058 0.155 7.923 1.770 2.7000 0.058 0.158 8.080 1.770 2.7500 0.058 0.161 8.234 1.770 2.8000 0.058 0.163 8.385 1.770 2.8500 0.058 0.166 8.533 1.770 2.9000 0.058 0.169 8.679 1.770 2.9500 0.058 0.172 8.822 1.770 3.0000 0.058 0.175 8.964 1.770 3.0500 0.058 0.178 9.103 1.770 3.1000 0.058 0.181 9.239 1.770 3.1500 0.058 0.184 9.374 1.770 3.2000 0.058 0.187 9.507 1.770 3.2500 0.058 0.190 9.638 1.770 3.3000 0.058 0.193 9.768 1.770 3.3500 0.058 0.196 9.896 1.770 3.4000 0.058 0.199 10.02 1.770 3.4500 0.058 0.202 10.14 1.770 3.5000 0.058 0.204 10.27 1.770 3.5500 0.058 0.207 10.39 1.770 3.6000 0.058 0.210 10.51 1.770 3.6500 0.058 0.213 10.63 1.770 3.7000 0.058 0.216 10.74 1.770 3.7500 0.058 0.219 10.86 1.770 3.8000 0.058 0.222 10.97 1.770 3.8500 0.058 0.225 11.09 1.770 3.9000 0.058 0.228 11.20 1.770 3.9500 0.058 0.231 11.31 1.770 4.0000 0.058 0.234 11.42 1.770 4.0500 0.058 0.237 11.53 1.770 4.1000 0.058 0.240 11.64 1.770 4.1500 0.058 0.242 11.75 1.770 4.2000 0.058 0.245 11.85 1.770 4.2500 0.058 0.248 11.96 1.770 4.3000 0.058 0.251 12.06 1.770 4.3500 0.058 0.254 12.17 1.770 4.4000 0.058 0.257 12.27 1.770 4.4500 0.058 0.260 12.37 1.770 4.5000 0.058 0.263 12.47 1.770 4.5500 0.058 0.266 12.57 1.770 ___________________________________________________________________ Name : Bypass Bypass: Yes GroundWater: No Pervious Land Use acre A B, Lawn, Mod .324 Pervious Total 0.324 Impervious Land Use acre ROADS FLAT 0.113 Impervious Total 0.113 Basin Total 0.437 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:4.181 Total Impervious Area:0.225 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0.976 Total Impervious Area:3.43 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.081729 5 year 0.114727 10 year 0.139552 25 year 0.174485 50 year 0.203218 100 year 0.234375 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.044039 5 year 0.065807 10 year 0.08299 25 year 0.108126 50 year 0.129519 100 year 0.153356 ___________________________________________________________________ Stream Protection Duration Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1956 0.107 0.048 1957 0.111 0.082 1958 0.057 0.032 1959 0.075 0.038 1960 0.089 0.044 1961 0.072 0.045 1962 0.093 0.047 1963 0.138 0.109 1964 0.079 0.040 1965 0.078 0.051 1966 0.057 0.028 1967 0.070 0.041 1968 0.063 0.034 1969 0.055 0.028 1970 0.060 0.030 1971 0.086 0.037 1972 0.246 0.095 1973 0.072 0.035 1974 0.102 0.050 1975 0.070 0.035 1976 0.073 0.044 1977 0.106 0.053 1978 0.093 0.062 1979 0.102 0.051 1980 0.069 0.036 1981 0.144 0.133 1982 0.142 0.071 1983 0.142 0.071 1984 0.086 0.045 1985 0.069 0.033 1986 0.077 0.050 1987 0.088 0.057 1988 0.045 0.022 1989 0.146 0.089 1990 0.067 0.034 1991 0.236 0.171 1992 0.086 0.046 1993 0.177 0.089 1994 0.087 0.044 1995 0.118 0.058 1996 0.100 0.057 1997 0.056 0.032 1998 0.116 0.094 1999 0.073 0.041 2000 0.058 0.028 2001 0.055 0.027 2002 0.043 0.021 2003 0.091 0.044 2004 0.098 0.049 2005 0.061 0.031 2006 0.049 0.024 2007 0.089 0.065 2008 0.056 0.027 2009 0.065 0.032 2010 0.110 0.053 2011 0.052 0.027 ___________________________________________________________________ Stream Protection Duration Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.2459 0.1714 2 0.2356 0.1325 3 0.1766 0.1094 4 0.1462 0.0954 5 0.1438 0.0941 6 0.1418 0.0887 7 0.1416 0.0887 8 0.1380 0.0820 9 0.1184 0.0712 10 0.1161 0.0712 11 0.1112 0.0648 12 0.1097 0.0615 13 0.1069 0.0581 14 0.1064 0.0574 15 0.1024 0.0567 16 0.1021 0.0535 17 0.0999 0.0535 18 0.0984 0.0515 19 0.0928 0.0510 20 0.0925 0.0499 21 0.0907 0.0496 22 0.0889 0.0494 23 0.0885 0.0480 24 0.0882 0.0467 25 0.0871 0.0458 26 0.0865 0.0451 27 0.0862 0.0445 28 0.0862 0.0445 29 0.0791 0.0441 30 0.0776 0.0436 31 0.0774 0.0436 32 0.0754 0.0408 33 0.0734 0.0408 34 0.0734 0.0397 35 0.0719 0.0379 36 0.0716 0.0375 37 0.0704 0.0357 38 0.0697 0.0354 39 0.0689 0.0346 40 0.0685 0.0340 41 0.0671 0.0338 42 0.0653 0.0332 43 0.0627 0.0324 44 0.0613 0.0323 45 0.0601 0.0320 46 0.0576 0.0307 47 0.0571 0.0298 48 0.0566 0.0284 49 0.0563 0.0283 50 0.0557 0.0275 51 0.0553 0.0274 52 0.0550 0.0273 53 0.0521 0.0271 54 0.0492 0.0235 55 0.0450 0.0220 56 0.0431 0.0215 ___________________________________________________________________ Stream Protection Duration POC #1 The Facility PASSED The Facility PASSED. Flow(cfs) Predev Mit Percentage Pass/Fail 0.0409 2052 141 6 Pass 0.0425 1736 112 6 Pass 0.0441 1500 95 6 Pass 0.0458 1305 84 6 Pass 0.0474 1140 69 6 Pass 0.0491 971 57 5 Pass 0.0507 868 48 5 Pass 0.0523 749 41 5 Pass 0.0540 664 37 5 Pass 0.0556 595 37 6 Pass 0.0573 513 33 6 Pass 0.0589 465 25 5 Pass 0.0605 402 25 6 Pass 0.0622 355 23 6 Pass 0.0638 324 23 7 Pass 0.0655 295 21 7 Pass 0.0671 277 21 7 Pass 0.0687 249 21 8 Pass 0.0704 219 21 9 Pass 0.0720 200 19 9 Pass 0.0737 186 18 9 Pass 0.0753 165 17 10 Pass 0.0769 153 17 11 Pass 0.0786 139 15 10 Pass 0.0802 124 12 9 Pass 0.0819 115 11 9 Pass 0.0835 103 10 9 Pass 0.0851 90 9 10 Pass 0.0868 80 8 10 Pass 0.0884 72 8 11 Pass 0.0901 64 6 9 Pass 0.0917 60 6 10 Pass 0.0933 52 6 11 Pass 0.0950 46 5 10 Pass 0.0966 44 4 9 Pass 0.0983 40 4 10 Pass 0.0999 36 3 8 Pass 0.1015 34 3 8 Pass 0.1032 32 3 9 Pass 0.1048 30 3 10 Pass 0.1065 28 3 10 Pass 0.1081 24 3 12 Pass 0.1097 23 2 8 Pass 0.1114 21 2 9 Pass 0.1130 20 2 10 Pass 0.1147 20 2 10 Pass 0.1163 18 2 11 Pass 0.1179 18 2 11 Pass 0.1196 16 2 12 Pass 0.1212 15 2 13 Pass 0.1229 15 2 13 Pass 0.1245 15 2 13 Pass 0.1261 15 2 13 Pass 0.1278 15 2 13 Pass 0.1294 15 2 13 Pass 0.1311 15 2 13 Pass 0.1327 15 1 6 Pass 0.1343 15 1 6 Pass 0.1360 14 1 7 Pass 0.1376 13 1 7 Pass 0.1393 12 1 8 Pass 0.1409 12 1 8 Pass 0.1425 10 1 10 Pass 0.1442 9 1 11 Pass 0.1458 8 1 12 Pass 0.1475 7 1 14 Pass 0.1491 7 1 14 Pass 0.1507 7 1 14 Pass 0.1524 7 1 14 Pass 0.1540 7 1 14 Pass 0.1557 6 1 16 Pass 0.1573 6 1 16 Pass 0.1589 5 1 20 Pass 0.1606 5 1 20 Pass 0.1622 4 1 25 Pass 0.1639 4 1 25 Pass 0.1655 4 1 25 Pass 0.1671 4 1 25 Pass 0.1688 4 1 25 Pass 0.1704 3 1 33 Pass 0.1721 3 0 0 Pass 0.1737 3 0 0 Pass 0.1753 3 0 0 Pass 0.1770 2 0 0 Pass 0.1786 2 0 0 Pass 0.1803 2 0 0 Pass 0.1819 2 0 0 Pass 0.1835 2 0 0 Pass 0.1852 2 0 0 Pass 0.1868 2 0 0 Pass 0.1885 2 0 0 Pass 0.1901 2 0 0 Pass 0.1917 2 0 0 Pass 0.1934 2 0 0 Pass 0.1950 2 0 0 Pass 0.1967 2 0 0 Pass 0.1983 2 0 0 Pass 0.1999 2 0 0 Pass 0.2016 2 0 0 Pass 0.2032 2 0 0 Pass _____________________________________________________ ___________________________________________________________________ Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0.4402 acre-feet On-line facility target flow: 0.513 cfs. Adjusted for 15 min: 0.513 cfs. Off-line facility target flow: 0.2914 cfs. Adjusted for 15 min: 0.2914 cfs. ___________________________________________________________________ LID Report LID Technique Used for Total Volume Volume Infiltration Cumulative Percent Water Quality Percent Comment Treatment? Needs Through Volume Volume Volume Water Quality Treatment Facility (ac-ft.) Infiltration Infiltrated Treated (ac-ft) (ac-ft) Credit Trapezoidal Pond 1 POC N 472.11 N 100.00 Total Volume Infiltrated 472.11 0.00 0.00 100.00 0.00 0% No Treat. Credit Compliance with LID Standard 8 Duration Analysis Result = Passed ___________________________________________________________________ POC #2 was not reported because POC must exist in both scenarios and both scenarios must have been run.Perlnd and Implnd Changes No changes have been made. ___________________________________________________________________ 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. August 2018 GENERAL USE LEVEL DESIGNATION FOR BASIC AND PHOSPHORUS TREATMENT For Kristar/Oldcastle Precast, Inc. FloGard Perk Filter™ (using ZPC Filter Media) Ecology’s Decision: Based on Kristar/Oldcastle’s application submissions, including the Draft Technical Evaluation Report, dated April 2010, Ecology hereby issues the following use level designations: 1. General use level designation (GULD) for the Perk Filter™ for basic treatment:  Using a zeolite-perlite-carbon (ZPC) filter media as specified by Kristar/Oldcastle.  Sized at hydraulic loading rate of no more than 1.5 gpm/ft² of media surface area, per Table 1. Table 1. Design Flowrate per Cartridge Effective Cartridge Height (inches) 12 18 Cartridge Flowrate (gpm/cartridge) 6.8 10.2 2. General use level designation (GULD) for the Perk Filter™ for phosphorus treatment:  Using a zeolite-perlite-carbon (ZPC) filter media as specified by Kristar/Oldcastle.  Sized at hydraulic loading rate of no more than 1.5 gpm/ft² of media surface area, per Table 1. 3. Ecology approves Perk Filter™ units for treatment at the hydraulic loading rates shown in Table 1, and sized based on the water quality design flow rate for an off-line system. The internal weir in the inlet chamber functions as a bypass to route flow in excess of the water quality design flow rate around the treatment chamber. Calculate the water quality design flow rate using the following procedures:  Western Washington: For treatment installed upstream of detention or retention, the water quality design flow rate is the peak 15-minute flow rate as calculated using the latest version of the Western Washington Hydrology Model or other Ecology- approved continuous runoff model.  Eastern Washington: For treatment installed upstream of detention or retention, the water quality design flow rate is the peak 15-minute flow rate as calculated using one of the three methods described in Chapter 2.2.5 of the Stormwater Management Manual for Eastern Washington (SWMMEW) or local manual.  Entire State: For treatment installed downstream of detention, the water quality design flow rate is the full 2-year release rate of the detention facility. 4. These General Use Level Designations have no expiration date but may be revoked or amended by Ecology, and are subject to the conditions specified below. Ecology’s Conditions of Use: Perk Filter™ units shall comply with the following conditions: 1. Design, assemble, install, operate, and maintain Perk Filter™ units in accordance with Kristar/Oldcastle’s applicable manuals and documents and the Ecology Decision. 2. Each site plan must undergo Kristar/Oldcastle review and approval before site installation. This ensures that site grading and slope are appropriate for use of a Perk Filter™ unit. 3. Perk Filter™media shall conform to the specifications submitted to, and approved by, Ecology. 4. Maintenance: The required maintenance interval for stormwater treatment devices is often dependent upon the degree of pollutant loading from a particular drainage basin. Therefore, Ecology does not endorse or recommend a “one size fits all” maintenance cycle for a particular model/size of manufactured filter treatment device.  Typically, Kristar/Oldcastle designs PerkFilter systems for a target filter media replacement interval of 12 months. Maintenance includes removing accumulated sediment from the vault, and replacing spent cartridges with recharged cartridges.  Indications of the need for maintenance include effluent flow decreasing to below the design flow rate, as indicated by the scumline above the shoulder of the cartridge.  Owners/operators must inspect PerkFilter for a minimum of twelve months from the start of post-construction operation to determine site-specific maintenance schedules and requirements. You must conduct inspections monthly during the wet season, and every other month during the dry season. (According to the SWMMWW, the wet season in western Washington is October 1 to April 30. According to SWMMEW, the wet season in eastern Washington is October 1 to June 30). After the first year of operation, owners/operators must conduct inspections based on the findings during the first year of inspections.  Conduct inspections by qualified personnel, follow manufacturer’s guidelines, and use methods capable of determining either a decrease in treated effluent flowrate and/or a decrease in pollutant removal ability.  When inspections are performed, the following findings typically serve as maintenance triggers:  Accumulated vault sediment depths exceed an average of 2 inches, or  Accumulated sediment depths on the tops of the cartridges exceed an average of 0.5 inches, or  Standing water remains in the vault between rain events, or  Bypass occurs during storms smaller than the design storm.  Note: If excessive floatables (trash and debris) are present, perform a minor maintenance consisting of gross solids removal, not cartridge replacement. 5. Discharges from the Perk Filter™ units shall not cause or contribute to water quality standards violations in receiving waters. Applicant: Kristar/Oldcastle Precast, Inc. Applicant’s Address: 5331 SW Macadam Avenue Suite 376 Portland, OR 97239 Application Documents:  Perk Filter™ Final Report, prepared by: Office of Water Programs, California State University, Sacramento (September 2007)  Verification Phase of Perk Filter™ Tests with Zeolite-Perlite-Carbon Media and Zeolite- Carbon Media (August 2007)  Quality Assurance Project Plan KriStar Perk Filter™ Stormwater Treatment Performance Monitoring Project, October 2008 Draft  Technical Evaluation Report Volume 1: KriStar Perk Filter™ Stormwater Treatment System Performance Monitoring, April 2010  Technical Evaluation Report Volume 2 - Appendices: KriStar Perk Filter™ Stormwater Treatment System Performance Monitoring, April 2010. Applicant’s Use Level Request:  General use level designation as a basic and Phosphorus treatment device in accordance with Ecology’s Guidance for Evaluating Emerging Stormwater Treatment Technologies Technology Assessment Protocol – Ecology (TAPE) January 2011 Revision. Applicant’s Performance Claims:  Capability to remove 80% of total suspended solids from stormwater runoff from sites with influent concentrations between 100 mg/L and 200 mg/L and provide effluent concentrations of 20 mg/L or less with influent concentrations less than 100 mg/L given a typical particle size distribution.  Capability to remove 50% of Total Phosphorus from stormwater runoff from sites with influent concentrations between 0.1 mg/l and 0.5 mg/l. Findings of Fact:  Based on laboratory testing at a flowrate of 12 GPM per filter, the Perk Filter™ containing ZPC media had an average total suspended solids removal efficiency of 82% using Sil-Co-Sil 106 with an average influent concentration of 102 mg/L and zero initial sediment loading.  Based on field-testing at a flowrate of 0.57 GPM/inch of cartridge height (17.25 inch diameter cartridge) (1.5 gpm per sq ft filter surface area), the Perk Filter™ containing ZPC media had an average total suspended solids removal efficiency of 82.4% for an influent concentration between 20 mg/L and 200 mg/l. The Perk Filter™ containing ZPC media had an average removal efficiency of 85.2% for an influent concentration between 100 mg/l and 200 mg/l. Removal rates fell over time and dropped below 80% after approximately 10 months.  Based on field testing at a flowrate of 0.57 GPM/inch of cartridge height (17.25 inch diameter cartridge) (1.5 gpm per sq ft filter surface area), the Perk Filter™ containing ZPC media had an average total Phosphorus removal efficiency of 62.4% for an influent concentration between 0.1 mg/L and 0.5 mg/l. Removal rates tended to remain relatively constant during the 10 months of monitoring.  Field Testing indicates that sediment accumulation in the Sediment Gallery during the 10 months of sampling was within the available volume for sediment. Thus, maintenance at a 6-month frequency (vacuuming of sediment from Inlet Gallery) as suggested by the manufacturer is sufficient.  Filter flows during bypass events utilize the full 30-inch height of the filter. Without bypass, an unknown amount of filter is used. Comparing the flow through the filter during bypass events with the design flow rate shows that the Kristar/Oldcastle system falls below the design flow rate after approximately 10 months of operation.  Percent removal of TSS falls below 80% after approximately 10 months. There are earlier data points below 80% but these are from low influent concentration storms Other Perk Filter™ Related Issues to be Addressed By the Company: 1. Kristar/Oldcastle may perform additional monitoring to better determine the maintenance frequency for the filters with respect to design flow rate and Total Suspended Solids removal. Presentation of additional data may result in a modification to the requirements in this Use Level designation document. Technology Description: Download at www.kristar.com Contact Information: Applicant: Jay Holtz, P.E. Engineering Manager Kristar/Oldcastle Precast, Inc. 5331 SW Macadam Avenue Suite 376 Portland, OR 97239 (971) 271-0796 jay.holtz@oldcastle.com Applicant website: www.kristar.com Ecology web link: http://www.ecy.wa.gov/programs/wq/stormwater/newtech/index.html Ecology: Douglas C. Howie, P.E. Department of Ecology Water Quality Program (360) 407-6444 douglas.howie@ecy.wa.gov Revision History Date Revision March 2008 Original Draft use-level-designation document June 2010 Revise Use Level to General January 2013 Modified Design Storm Description, added Revision Table, formatted document to match Ecology standard May 2014 Revised Company name and contact information June 2016 Designated device for off-line sizing August 2018 Revised Address and phone number for Oldcastle APPENDIX D Geotechncial Engineer’s Reports 1015 East 4th Avenue, Olympia, Washington 98506 Phone: 360.754.2128 Fax: 360.754.9299 July 12, 2019 C & E Developments LLC PO Box 2983 Yelm, Washington 98597 Attention: Casey Peterson Report Geotechnical and Stormwater Investigation Wyndstone Development Proposed Multi-Family Residential 15025 Tahoma Boulevard SE Yelm, Washington Project No. 1142-001-01 INTRODUCTION Insight Geologic is pleased to present our report of subsurface conditions at the location of your proposed Wyndstone multi-family residential development to be located at 15025 Tahoma Boulevard SE in Yelm, Washington. The location of the site is shown relative to surrounding physical features in the Vicinity Map, Figure 1. The site of the proposed project consists of a single parcel of property (Thurston County Tax Parcel No. 21724420300), comprising approximately 4.3 acres. The project will include four, multi-family, multi-story residential buildings with appurtenant parking and drive areas. Stormwater runoff from roads and parking areas is to be infiltrated to the subsurface in the northern portion of the property. SCOPE OF SERVICES The objective of our services was to evaluate subsurface conditions on the property as a basis for evaluating suitability of the soils for the proposed building and parking areas, as well as evaluating the soils for stormwater infiltration. Our specific scope of services included the following tasks: Stormwater Investigation 1. Provided for the location of subsurface utilities on the site. We conducted this task by notifying the “One Call” system. 2. Conducted a site reconnaissance to evaluate and mark proposed boring locations at the site and for truck-mounted drilling rig access. 3. Drilled two (2) borings in the location of the proposed stormwater disposal structure at the site using a truck-mounted drilling rig. Wyndstone Geotechnical and Stormwater Investigation Report July 12, 2019 File No. 1142−001−01 2 Insight Geologic, Inc. 4. Installed one (1), 2-inch diameter monitoring well, constructed of PVC casing. The well was finished inside a locking steel cover installed flush with the surrounding grade. 5. Collected soil samples continuously during drilling to the full depth of the borings. 6. Maintained logs of the soils encountered in the boreholes and provided well construction details. Soils were described in general accordance with the Unified Soil Classification System and presented on the field logs. 7. Conducted an evaluation of stormwater infiltration rates using the detailed method outlined in Ecology’s 2014 Stormwater Management Manual, as adopted by the City of Yelm, and provide a design infiltration rate for stormwater infiltration. Geotechnical Investigation 8. Excavated a series of six (6) exploratory test pits across the project site using a small, track- mounted excavator. The test pits were excavated to depths of between approximately 6 to 8 feet below ground surface (bgs) across the site. 9. Collected representative soil samples from the test pits for possible laboratory analysis. 10. Logged the soils exposed in the test pits in general accordance with ASTM D2487-06. 11. Provided for laboratory testing of seven (7) soil samples for gradation analyses to evaluate bearing capacity and for stormwater infiltration calculations. 12. Prepared a report summarizing our field activities including our recommendations for site preparation and grading, bearing capacity, seismic class, temporary and final cut slopes, earth pressures, and suitability of the on-site soils for use as fill. FINDINGS Surface Conditions The project site is a rectangular shaped parcel situated at an elevation of approximately 340 to 350 feet above mean sea level (MSL) and is currently occupied by a single-family residence. The property is bounded by Tahoma Boulevard SE to the north, Durant Street SE to the west, and residential properties to the south and east. The site gently slopes down to the north with an elevation drop of 10 feet across the site. The subject site is vegetated with grasses, scotch broom, and isolated stands of low growing trees and other shrubs. Geology Based on our review of available published geologic maps, Vashon age glacial recessional outwash gravel deposits underlie the project site. This material is described as poorly-sorted gravel and sand. This material was deposited by outwash rivers during the waning stages of the most recent glacial period in the Puget Sound region and is not glacially consolidated. Subsurface Explorations We explored subsurface conditions at the site on June 10 and June 14, 2019 by excavating six test pits and advancing two borings in the locations as shown on the Site Plan, Figure 2. The test pits were excavated by Insight Geologic using a track-mounted excavator. The exploratory borings were Wyndstone Geotechnical and Stormwater Investigation Report July 12, 2019 File No. 1142−001−01 3 Insight Geologic, Inc. completed by Holocene Drilling using a truck-mounted hollow stem auger drill rig. A geologist from Insight Geologic monitored the explorations and maintained a log of the conditions encountered. The test pits were completed to depths of 6 to 8 feet bgs, and the borings were completed to depths of between 23 and 36.5 feet bgs. The soils were visually classified in general accordance with the system described in ASTM D2487-06. A copy of the explorations is contained in Attachment A. Soil Conditions The explorations were generally consistent across the site. Underlying approximately 6 inches of sod, we generally encountered between 1.5 to 2 feet of dark brown, poorly- to well-graded gravel and sand with cobbles and varying levels of silt and organics (GP-GM, GP), in a loose and moist condition. Underlying the dark brown unit, we encountered brown poorly- to well-graded gravels with cobbles and varying percentages of sand (GP, GW) to poorly graded sands with gravels and cobbles and varying percentages of silt (SP, SP-SM), in a loose to very dense and moist to wet condition to the base of the explorations. In general, soils increased in compaction with depth. The soils encountered are consistent with Nisqually loamy fine sand and Spanaway gravelly sandy loam, which are mapped for the area. In general, the Nisqually loamy fine sand is mapped along the north quarter of the site, while the Spanaway gravelly sandy loam is mapped on the remainder of the property. These soils are generally formed from sandy and gravely glacial outwash and generally has restrictive layers occurring greater than 7 feet below grade. Percolation is generally high, with rates between 1.98 and 5.95 inches per hour, according to the U.S. Department of Agriculture Soil Survey. Groundwater Conditions Groundwater was encountered in boring MW-1 at a depth of 32 feet bgs. Groundwater was not encountered in any of the remaining explorations completed on-site. The explorations were completed during the summer season at a time that generally correlates to a lower groundwater elevation. In addition, no evidence of high groundwater was encountered within the explorations at the site. Laboratory Testing We selected seven soil samples for gradation analyses in general accordance with ASTM D422 to define soil class and obtain parameters for stormwater infiltration calculations. Our laboratory test results are provided in Attachment B. STORMWATER INFILTRATION We completed a stormwater infiltration rate evaluation in general accordance with the Washington State Department of Ecology Stormwater Manual for Western Washington (2014 Manual) as adopted by the City of Yelm. For the purposes of this evaluation, we selected Method 3 “Soil Grain Size Analysis Method”. The 2014 Manual utilizes the relationship between the D10, D60, and D90 results of the ASTM grain-size distribution analyses, along with site specific correction factors to estimate long- term design infiltration rates of each infiltration facility. Based on our gradation analyses, we estimate that the long-term design infiltration rate (Fdesign) for the proposed stormwater infiltration is between 1.6 and 20 inches per hour, after applying the appropriate correction factors. The range of infiltration rate is the result of varying percentages of fines in the soil Wyndstone Geotechnical and Stormwater Investigation Report July 12, 2019 File No. 1142−001−01 4 Insight Geologic, Inc. profile. Our calculations assume that the stormwater infiltration will occur at a depth of at least 3 feet bgs or below the upper gravel with sand and silt unit. Changes to these infiltration rates are possible depending on the depth to groundwater during winter months. For the purposes of stormwater infiltration on this project, we recommend using an infiltration rate of 2.9 inches per hour for the pond area and 5 inches per hour for roof downspouts in the central portion of the site. Table 1. Design Infiltration Rates – Detailed Method Exploration Unit Depth Range (feet) D10 Value D60 Value D90 Value Long Term Design Infiltration Rate (Inches per hour) TP-2 GW 3.0 – 8.0 7.9 44 130 20 TP-5 SP 2.0 – 8.0 0.31 3.2 51 1.6 MW-1 GP 25.0 – 26.5 0.35 14 30 2.9 MW-1 GW 30.0 – 31.5 0.26 8.5 18 B-1 SP-SM 10.0 – 11.5 0.14 2.1 25 SEISMIC DESIGN CONSIDERATIONS General We understand that seismic design will likely be performed using the 2015 IBC standards. The following parameters may be used in computing seismic base shear forces: Table 2. 2015 IBC Seismic Design Parameters Spectral Response Accel. at Short Periods (SS) = 1.25 Spectral Response Accel. at 1 Second Periods (S1) = 0.50 Site Class = D Site Coefficient (FA) = 1.0 Site Coefficient (FV) = 1.5 A full report for the seismic design parameters is presented in Attachment C. Ground Rupture Because of the location of the site with respect to the nearest known active crustal faults, and the presence of a relatively thick layer of glacial outwash deposits, it is our opinion that the risk of ground rupture at the site due to surface faulting is low. Soil Liquefaction Liquefaction refers to a condition where vibration or shaking of the ground, usually from earthquake forces, results in the development of excess pore water pressures in saturated soils, and a subsequent loss of stiffness in the soil occurs. Liquefaction also causes a temporary reduction of soil shear strength and bearing capacity, which can cause settlement of the ground surface above the liquefied Wyndstone Geotechnical and Stormwater Investigation Report July 12, 2019 File No. 1142−001−01 5 Insight Geologic, Inc. soil layers. In general, soils that are most susceptible to liquefaction include saturated, loose to medium dense, clean to silty sands and non-plastic silts within 50 feet of ground surface. Based on our review of the Liquefaction Susceptibility Map of Thurston County (Palmer, 2004), the project site is identified to have a very low potential risk for soil liquefaction. Based on our experience with detailed seismic studies in the Yelm area, including areas that are mapped within the same recessional outwash soil deposits as the project site, we concur with the reviewed map. It is our opinion that there is a low risk for soil liquefaction at the site. Seismic Compression Seismic compression is defined as the accrual of contractive volumetric strains in unsaturated soils during strong shaking from earthquakes (Stewart et al., 2004). Loose to medium dense clean sands and non-plastic silts are particularly prone to seismic compression settlement. Seismic compression settlement is most prevalent on slopes, but it can also occur on flat ground. It is our opinion that the upper 15 feet of the soil profile at the site has a moderate risk for seismic compression settlement. Seismic Settlement Discussion Based on the materials encountered in our explorations, it is our preliminary opinion that seismic settlements (liquefaction-induced plus seismic compression) could potentially total a few inches at the site as the result of an IBC design level earthquake. We are available upon request to perform deep subsurface explorations and detailed seismic settlement estimates during the design phase. Seismic Slope Instability The maximum inclination of the site is approximately 2 percent and we did not observe signs of slope instability during our site work. In our opinion, there is a very low risk of seismic slope instability at the project site under current conditions. Lateral Spreading Lateral spreading involves the lateral displacement of surficial blocks of non-liquefied soil when an underlying soil layer liquefies. Lateral spreading generally develops in areas where sloping ground or large grade changes are present. Based on our limited understanding of the subsurface conditions at the site, it is our opinion that there is a low risk for the development of lateral spreading as a result of an IBC design level earthquake. CONCLUSIONS AND RECOMMENDATIONS General Based on the results of our subsurface explorations and engineering analyses, it is our opinion that the proposed development is feasible from a geotechnical standpoint. We recommend that the proposed structures be supported on shallow concrete foundations that are designed using an allowable soil bearing capacity of 2,500 pounds per square foot (psf). The soils encountered in our explorations are typically in a loose condition near ground surface. To limit the potential for structure settlement, we recommend that shallow foundations and slabs-on-grade be established on a minimum 1-foot thick layer of structural fill. Depending on final grading plans and Wyndstone Geotechnical and Stormwater Investigation Report July 12, 2019 File No. 1142−001−01 6 Insight Geologic, Inc. the time of year earthwork is performed; it could be practical to reuse the on-site soils as structural fill under the foundations/slabs. Stormwater infiltration at the site is feasible. We propose a design infiltration rate of 2.9 inches per hour for the stormwater infiltration systems, based on the assumption that stormwater infiltration will occur within the clean gravels and sands below a depth of about 3 feet bgs. This value is based on an idealized soil column located in the area of the proposed stormwater infiltration trench on the north side of the site. It may be possible to increase the infiltration rate with additional testing such as a Pilot Infiltration Test in the location of the proposed infiltration facility. Alternatively, based on the U.S. Department of Agriculture Soil Survey map, areas of increased infiltration may be present within the Spanaway gravelly sandy loam mapped on the southern portions of the site. Additional evaluation of this area at depth would be required for a more detailed analysis. Earthwork General We anticipate that site development earthwork will include removing the existing vegetation, stripping sod/topsoil materials, preparing subgrades, excavating for utility trenches, and placing and compacting structural fill. We expect that the majority of site grading can be accomplished with conventional earthmoving equipment in proper working order. Our explorations did not encounter appreciable amounts of debris or unsuitable soils associated with past site development. Still, it is possible that concrete slabs, abandoned utility lines or other development features could be encountered during construction. The contractor should be prepared to deal with these conditions. Clearing and Stripping Clearing and stripping should consist of removing surface and subsurface deleterious materials including sod/topsoil, trees, brush, debris and other unsuitable loose/soft or organic materials. Stripping and clearing should extend at least 5 feet beyond all structures and areas to receive structural fill. We estimate that a stripping depth of about 0.5 feet will be required to remove the sod encountered in several of our explorations. Deeper stripping depths may be required if additional unsuitable soils are exposed during stripping operations. We recommend that trees be removed by overturning so that the majority of roots are also removed. Depressions created by tree or stump removal should be backfilled with structural fill and properly compacted. Subgrade Preparation After stripping and excavating to the proposed subgrade elevation, and before placing structural fill or foundation concrete, the exposed subgrade should be thoroughly compacted to a firm and unyielding condition. The exposed subgrade should then be proof-rolled using loaded, rubber-tired heavy equipment. We recommend that Insight Geologic be retained to observe the proof-rolling prior to placement of structural fill or foundation concrete. Areas of limited access that cannot be proof-rolled Wyndstone Geotechnical and Stormwater Investigation Report July 12, 2019 File No. 1142−001−01 7 Insight Geologic, Inc. can be evaluated using a steel probe rod. If soft or otherwise unsuitable areas are revealed during proof-rolling or probing, that cannot be compacted to a stable and uniformly firm condition, we generally recommend that: 1) the subgrade soils be scarified (e.g., with a ripper or farmer’s disc), aerated and recompacted; or 2) the unsuitable soils be overexcavated and replaced with structural fill. Temporary Excavations and Groundwater Handling Excavations deeper than 4 feet should be shored or laid back at a stable slope if workers are required to enter. Shoring and temporary slope inclinations must conform to the provisions of Title 296 Washington Administrative Code (WAC), Part N, “Excavation, Trenching and Shoring.” Regardless of the soil type encountered in the excavation, shoring, trench boxes or sloped sidewalls were required under the Washington Industrial Safety and Health Act (WISHA). The contract documents should specify that the contractor is responsible for selecting excavation and dewatering methods, monitoring the excavations for safety and providing shoring, as required, to protect personnel and structures. In general, temporary cut slopes should be inclined no steeper than about 1.5H:1V (horizontal: vertical). This guideline assumes that all surface loads are kept at a minimum distance of at least one- half the depth of the cut away from the top of the slope, and that significant seepage is not present on the slope face. Flatter cut slopes were necessary where significant seepage occurs or if large voids are created during excavation. Some sloughing and raveling of cut slopes should be expected. Temporary covering with heavy plastic sheeting should be used to protect slopes during periods of wet weather. We anticipate that if perched groundwater is encountered during construction can be handled adequately with sumps, pumps, and/or diversion ditches. Groundwater handling needs will generally be lower during the late summer and early fall months. We recommend that the contractor performing the work be made responsible for controlling and collecting groundwater encountered during construction. Permanent Slopes We do not anticipate that permanent slopes will be utilized for the proposed project. If permanent slopes are necessary, we recommend the slopes be constructed at a maximum inclination of 2H:1V. Where 2H:1V permanent slopes are not feasible, protective facings and/or retaining structures should be considered. To achieve uniform compaction, we recommend that fill slopes be overbuilt and subsequently cut back to expose well-compacted fill. Fill placement on slopes should be benched into the slope face and include keyways. The configuration of the bench and keyway depends on the equipment being used. Bench excavations should be level and extend into the slope face. We recommend that a vertical cut of about 3 feet be maintained for benched excavations. Keyways should be about 1-1/2 times the width of the equipment used for grading or compaction. Erosion Control We anticipate that erosion control measures such as silt fences, straw bales and sand bags will generally be adequate during development. Temporary erosion control should be provided during Wyndstone Geotechnical and Stormwater Investigation Report July 12, 2019 File No. 1142−001−01 8 Insight Geologic, Inc. construction activities and until permanent erosion control measures are functional. Surface water runoff should be properly contained and channeled using drainage ditches, berms, swales, and tightlines, and should not discharge onto sloped areas. Any disturbed sloped areas should be protected with a temporary covering until new vegetation can take effect. Jute or coconut fiber matting, excelsior matting or clear plastic sheeting is suitable for this purpose. Graded or disturbed slopes should be tracked in-place with the equipment running perpendicular to the slope contours so that the track marks provide a texture to help resist erosion. Ultimately, erosion control measures should be in accordance with local regulations and should be clearly described on project plans. Wet Weather Earthwork Some of the near surface soils contain up to about 7 percent fines. When the moisture content of the soil is more than a few percent above the optimum moisture content, the soil will become unstable and it may become difficult or impossible to meet the required compaction criteria. Disturbance of near surface soils should be expected if earthwork is completed during periods of wet weather. The wet weather season in this area generally begins in October and continues through May. However, periods of wet weather may occur during any month of the year. If wet weather earthwork is unavoidable, we recommend that:  The ground surface is sloped so that surface water is collected and directed away from the work area to an approved collection/dispersion point.  Earthwork activities not take place during periods of heavy precipitation.  Slopes with exposed soil be covered with plastic sheeting or otherwise protected from erosion.  Measures are taken to prevent on-site soil and soil stockpiles from becoming wet or unstable. Sealing the surficial soil by rolling with a smooth-drum roller prior to periods of precipitation should reduce the extent that the soil becomes wet or unstable.  Construction traffic is restricted to specific areas of the site, preferably areas that are surfaced with materials not susceptible to wet weather disturbance.  A minimum 1-foot thick layer of 4- to 6-inch quarry spalls is used in high traffic areas of the site to protect the subgrade soil from disturbance.  Contingencies are included in the project schedule and budget to allow for the above elements. Structural Fill Materials General Material used for structural fill should be free of debris, organic material and rock fragments larger than 3 inches. The workability of material for use as structural fill will depend on the gradation and moisture content of the soil. As the amount of fines increases, soil becomes increasingly more sensitive to small changes in moisture content and adequate compaction becomes more difficult or impossible to achieve. Wyndstone Geotechnical and Stormwater Investigation Report July 12, 2019 File No. 1142−001−01 9 Insight Geologic, Inc. On-Site Soil We anticipate that the majority of the on-site soils encountered during construction will consist of gravels, cobbles and sands, located at or near the surface of the site. It is our opinion, that this material is a suitable source for structural fill during a significant portion of the year. On-site materials used as structural fill should be free of roots, organic matter and other deleterious materials and particles larger than 3 inches in diameter. Significant quantities of material greater than 3 inches in diameter were observed during our site explorations. This material will cause significand difficulties in soil grading and compaction efforts. We recommend that the material greater than 3 inches in diameter be screened and removed or crushed for reuse on-site. Select Granular Fill Select granular fill should consist of imported, well-graded sand and gravel or crushed rock with a maximum particle size of 3 inches and less than 5 percent passing a U.S. Standard No. 200 sieve based on the minus ¾-inch fraction. Organic matter, debris or other deleterious material should not be present. In our experience, “gravel borrow” as described in Section 9-03.14(1) of the 2018 WSDOT Standard Specifications is typically a suitable source for select granular fill during periods of wet weather, provided that the percent passing a U.S. Standard No. 200 sieve is less than 5 percent based on the minus ¾-inch fraction. Structural Fill Placement and Compaction General Structural fill should be placed on an approved subgrade that consists of uniformly firm and unyielding inorganic native soils or compacted structural fill. Structural fill should be compacted at a moisture content near optimum. The optimum moisture content varies with the soil gradation and should be evaluated during construction. Structural fill should be placed in uniform, horizontal lifts and uniformly densified with vibratory compaction equipment. The maximum lift thickness will vary depending on the material and compaction equipment used, but should generally not exceed the loose thicknesses provided on Table 3. Structural fill materials should be compacted in accordance with the compaction criteria provided in Table 4. Table 3. Recommended Uncompacted Lift Thickness Compaction Equipment Recommended Uncompacted Fill Thickness (inches) Granular Materials Maximum Particle Size  1 1/2 inch Granular Materials Maximum Particle Size > 1 1/2 inch Hand Tools (Plate Compactors and Jumping Jacks) 4 – 8 Not Recommended Rubber-tire Equipment 10 – 12 6 – 8 Light Roller 10 – 12 8 – 10 Heavy Roller 12 – 18 12 – 16 Hoe Pack Equipment 18 – 24 12 – 16 Note: The above table is intended to serve as a guideline and should not be included in the project specifications. Wyndstone Geotechnical and Stormwater Investigation Report July 12, 2019 File No. 1142−001−01 10 Insight Geologic, Inc. Table 4. Recommended Compaction Criteria in Structural Fill Zones Fill Type Percent Maximum Dry Density Determined by ASTM Test Method D 1557 at ±3% of Optimum Moisture 0 to 2 Feet Below Subgrade > 2 Feet Below Subgrade Pipe Zone Imported or On-site Granular, Maximum Particle Size < 1-1/4-inch 95 95 ----- Imported or On-site Granular, Maximum Particle Size >1-1/4-inch N/A (Proof-roll) N/A (Proof-roll) ----- Trench Backfill1 95 92 90 Note: 1Trench backfill above the pipe zone in nonstructural areas should be compacted to at least 85 percent. Shallow Foundation Support General We recommend that the proposed structures be founded on continuous wall or isolated column footings, bearing on a minimum 1-foot thick overexcavation and replacement with compacted structural fill where underlying soils are not able to be compacted as structural fill. The structural fill zone should extend to a horizontal distance equal to the overexcavation depth on each side of the footing. The actual overexcavation depth will vary, depending on the conditions encountered. We recommend that a representative from Insight Geologic observe the foundation surfaces before overexcavation, and before placing structural fill in overexcavations. This representative should confirm that adequate bearing surfaces have been prepared and that the soil conditions are as anticipated. Unsuitable foundation bearing soils should be recompacted or removed and replaced with compacted structural fill, as recommended by the geotechnical engineer. Bearing Capacity and Footing Dimensions We recommend an allowable soil bearing pressure of 2,500 psf for shallow foundations that are supported as recommended. This allowable bearing pressure applies to long-term dead and live loads exclusive of the weight of the footing and any overlying backfill. The allowable soil bearing pressure can be increased by one-third when considering total loads, including transient loads such as those induced by wind and seismic forces. We recommend a minimum width of 18 inches for continuous wall footings and 2 feet for isolated column footings. For settlement considerations, we have assumed a maximum width of 4 feet for continuous wall footings and 6 feet for isolated column footings. Perimeter footings should be embedded at least 12 inches below the lowest adjacent grade where the ground is flat. Interior footings should be embedded a minimum of 6 inches below the nearest adjacent grade. Settlement We estimate that total settlement of footings that are designed and constructed as recommended should be less than 1 inch. We estimate that differential settlements should be ½ inch or less between Wyndstone Geotechnical and Stormwater Investigation Report July 12, 2019 File No. 1142−001−01 11 Insight Geologic, Inc. comparably loaded isolated footings or along 50 feet of continuous footing. We anticipate that the settlement will occur essentially as loads are applied during construction. Lateral Load Resistance Lateral loads on shallow foundation elements may be resisted by passive resistance on the sides of footings and by friction on the base of footings. Passive resistance may be estimated using an equivalent fluid density of 303 pounds per cubic foot (pcf), assuming that the footings are backfilled with structural fill. Frictional resistance may be estimated using 0.25 for the coefficient of base friction. The lateral resistance values provided above incorporate a factor of safety of 1.5. The passive earth pressure and friction components can be combined, provided that the passive component does not exceed two-thirds of the total. The top foot of soil should be neglected when calculating passive resistance, unless the foundation perimeter area is covered by a slab-on-grade or pavement. Slabs-On-Grade Slabs-on-grade should be established on a minimum 1-foot thick section of structural fill extending to an approved bearing surface. A modulus of vertical subgrade reaction (subgrade modulus) can be used to design slabs-on-grade. The subgrade modulus varies based on the dimensions of the slab and the magnitude of applied loads on the slab surface; slabs with larger dimensions and loads are influenced by soils to a greater depth. We recommend a modulus value of 300 pounds per cubic inch (pci) for design of on-grade floor slabs with floor loads up to 500 psf. We are available to provide alternate subgrade modulus recommendations during design, based on specific loading information. We recommend that slabs-on-grade in interior spaces be underlain by a minimum 4-inch thick capillary break layer to reduce the potential for moisture migration into the slab. The capillary break material should consist of a well-graded sand and gravel or crushed rock containing less than 5 percent fines based on the fraction passing the ¾-inch sieve. The 4-inch thick capillary break layer can be included when calculating the minimum 1-foot thick structural fill section beneath the slab. If dry slabs are required (e.g., where adhesives are used to anchor carpet or tile to the slab), a waterproofing liner should be placed below the slab to act as a vapor barrier. Subsurface Drainage It is our opinion that foundation footing drains and underslab drains are likely unnecessary for the proposed structures. The majority of subsurface site soils are well draining and it is unlikely that subsurface drains would produce water. The soils are suitable for roof runoff drywells and should be classified as Group A for the purposes of design. Conventional Retaining Walls General We do not anticipate that retaining walls will be utilized for the proposed project. We should be contacted during the design phase to review retaining wall plans and provide supplemental recommendations, if needed. Wyndstone Geotechnical and Stormwater Investigation Report July 12, 2019 File No. 1142−001−01 12 Insight Geologic, Inc. Drainage Positive drainage is imperative behind any retaining structure. This can be accomplished by using a zone of free-draining material behind the wall with perforated pipes to collect water seepage. The drainage material should consist of coarse sand and gravel containing less than 5 percent fines based on the fraction of material passing the ¾-inch sieve. The wall drainage zone should extend horizontally at least 12 inches from the back of the wall. If a stacked block wall is constructed, we recommend that a barrier such as a non-woven geotextile filter fabric be placed against the back of the wall to prevent loss of the drainage material through the wall joints. A perforated smooth-walled rigid PVC pipe, having a minimum diameter of 4 inches, should be placed at the bottom of the drainage zone along the entire length of the wall. Drainpipes should discharge to a tightline leading to an appropriate collection and disposal system. An adequate number of cleanouts should be incorporated into the design of the drains in order to provide access for regular maintenance. Roof downspouts, perimeter drains or other types of drainage systems should not be connected to retaining wall drain systems. Design Parameters We recommend an active lateral earth pressure of 37 pcf (equivalent fluid density) for a level backfill condition. This assumes that the top of the wall is not structurally restrained and is free to rotate. For restrained walls that are fixed against rotation (at-rest condition), an equivalent fluid density of 56 pcf can be used for the level backfill condition. For seismic conditions, we recommend a uniform lateral pressure of 14H psf (where H is the height of the wall) be added to the lateral pressures. This seismic pressure assumes a peak ground acceleration of 0.32 g. Note that if the retaining system is designed as a braced system but is expected to yield a small amount during a seismic event, the active earth pressure condition may be assumed and combined with the seismic surcharge. The recommended earth pressure values do not include the effects of surcharges from surface loads or structures. If vehicles were operated within one-half the height of the wall, a traffic surcharge should be added to the wall pressure. The traffic surcharge can be approximated by the equivalent weight of an additional 2 feet of backfill behind the wall. Other surcharge loads, such as construction equipment, staging areas and stockpiled fill, should be considered on a case-by-case basis. DOCUMENT REVIEW AND CONSTRUCTION OBSERVATION We recommend that we be retained to review the portions of the plans and specifications that pertain to earthwork construction and stormwater infiltration. We recommend that monitoring, testing and consultation be performed during construction to confirm that the conditions encountered are consistent with our explorations and our stated design assumptions. Insight Geologic would be pleased to provide these services upon request. REFERENCES International Code Council, International Building Code, 2015. Seismic Compression of As-compacted Fill Soils with Variable Levels of Fines Content and Fines Plasticity, Department of Civil and Environmental Engineering, University of California, Los Angeles, July 2004. Wyndstone Geotechnical and Stormwater Investigation Report July 12, 2019 File No. 1142−001−01 13 Insight Geologic, Inc. Washington State Department of Transportation (WSDOT), Standard Specifications for Road, Bridge and Municipal Construction Manual, 2018. Washington State Department of Ecology (WSDOE), Stormwater Management Manual of Western Washington, 2014. LIMITATIONS We have prepared this geotechnical and stormwater investigation report for the exclusive use of C & E Developments LLC and their authorized agents, for the proposed development located at 15025 Tahoma Boulevard SE in Yelm, Washington. Within the limitations of scope, schedule and budget, our services have been executed in accordance with generally accepted practices in the field of geotechnical engineering in this area at the time this report was prepared. No warranty or other conditions, expressed or implied, should be understood. Please refer to Attachment D titled “Report Limitations and Guidelines for Use” for additional information pertaining to use of this report. __________________________ We appreciate the opportunity to be of service to you on this project. Please contact us if you have questions or require additional information. Respectfully Submitted, Insight Geologic, Inc. William E. Halbert, L.E.G., L.HG. Principal Attachments Insight Geologic, Inc. FIGURES Insight Geologic, Inc. ATTACHMENT A EXPLORATION LOGS Insight Geologic, Inc. ATTACHMENT B LABORATORY ANALYSES RESULTS Job Name:Wyndstone Sample Location:TP-2 Job Number:1142-001-01 Sample Name:TP-2 0.5'-3.0' Date Tested:7/1/19 Depth:0.5 - 3 Feet Tested By:Kevin Vandehey 4.3% Percent Percent by Sieve Size Passing Size Fraction Weight 3.0 in. (75.0) 100.0 Coarse Gravel 68.7 1.5 in. (37.5) 51.9 Fine Gravel 9.7 3/4 in. (19.0) 31.3 3/8 in. (9.5-mm) 24.9 Coarse Sand 2.8 No. 4 (4.75-mm) 21.6 Medium Sand 6.9 No. 10 (2.00-mm) 18.8 Fine Sand 7.4 No. 20 (.850-mm) 15.9 No. 40 (.425-mm) 11.9 Fines 4.5 No. 60 (.250-mm) 8.6 Total 100.0 No. 100 (.150-mm) 6.1 No. 200 (.075-mm) 4.5 LL - - PL - - Pl - - D10 0.31 D30 17.00 D60 41.00 D90 65.00 Cc 22.74 Cu 132.26 ASTM Classification Group Name:Poorly Graded Gravel with Sand Symbol:GP Gradation Analysis Summary Data Moisture Content (%) Job Name:Wyndstone Sample Location:TP-2 Job Number:1142-001-01 Sample Name:TP-2 3.0'-8.0' Date Tested:7/1/19 Depth:3 - 8 Feet Tested By:Kevin Vandehey 1.2% Percent Percent by Sieve Size Passing Size Fraction Weight 3.0 in. (75.0) 64.7 Coarse Gravel 72.7 1.5 in. (37.5) 57.3 Fine Gravel 21.2 3/4 in. (19.0) 27.3 3/8 in. (9.5-mm) 12.4 Coarse Sand 3.2 No. 4 (4.75-mm) 6.0 Medium Sand 1.8 No. 10 (2.00-mm) 2.8 Fine Sand 0.7 No. 20 (.850-mm) 1.7 No. 40 (.425-mm) 0.9 Fines 0.2 No. 60 (.250-mm) 0.5 Total 100.0 No. 100 (.150-mm) 0.3 No. 200 (.075-mm) 0.2 LL - - PL - - Pl - - D10 7.90 D30 20.50 D60 44.00 D90 130.00 Cc 1.21 Cu 5.57 ASTM Classification Group Name:Well Graded Gravel Symbol:GW Gradation Analysis Summary Data Moisture Content (%) Job Name:Wyndstone Sample Location:TP-5 Job Number:1142-001-01 Sample Name:TP-5 0.5'-2.0' Date Tested:7/1/19 Depth:0.5 - 2 Feet Tested By:Kevin Vandehey 7.0% Percent Percent by Sieve Size Passing Size Fraction Weight 3.0 in. (75.0) 100.0 Coarse Gravel 47.3 1.5 in. (37.5) 67.9 Fine Gravel 15.5 3/4 in. (19.0) 52.7 3/8 in. (9.5-mm) 42.9 Coarse Sand 4.9 No. 4 (4.75-mm) 37.2 Medium Sand 15.6 No. 10 (2.00-mm) 32.3 Fine Sand 9.5 No. 20 (.850-mm) 26.6 No. 40 (.425-mm) 16.7 Fines 7.2 No. 60 (.250-mm) 11.5 Total 100.0 No. 100 (.150-mm) 9.2 No. 200 (.075-mm) 7.2 LL - - PL - - Pl - - D10 0.18 D30 1.40 D60 28.00 D90 60.00 Cc 0.39 Cu 155.56 ASTM Classification Group Name:Poorly Graded Gravel with Sand and Silt Symbol:GP-GM Gradation Analysis Summary Data Moisture Content (%) Job Name:Wyndstone Sample Location:TP-5 Job Number:1142-001-01 Sample Name:TP-5 2.0'-8.0' Date Tested:7/1/19 Depth:2 - 8 Feet Tested By:Kevin Vandehey 4.9% Percent Percent by Sieve Size Passing Size Fraction Weight 3.0 in. (75.0) 100.0 Coarse Gravel 31.3 1.5 in. (37.5) 81.7 Fine Gravel 7.3 3/4 in. (19.0) 68.7 3/8 in. (9.5-mm) 64.5 Coarse Sand 3.7 No. 4 (4.75-mm) 61.4 Medium Sand 39.1 No. 10 (2.00-mm) 57.7 Fine Sand 17.1 No. 20 (.850-mm) 48.6 No. 40 (.425-mm) 18.5 Fines 1.5 No. 60 (.250-mm) 5.2 Total 100.0 No. 100 (.150-mm) 2.6 No. 200 (.075-mm) 1.5 LL - - PL - - Pl - - D10 0.31 D30 0.55 D60 3.20 D90 51.00 Cc 0.30 Cu 10.32 ASTM Classification Group Name:Poorly Graded Sand with Gravel Symbol:SP Moisture Content (%) Gradation Analysis Summary Data Job Name:Wyndstone Sample Location:MW-1 Job Number:1142-001-01 Sample Name:MW-1 25.0'-26.5' Date Tested:7/1/19 Depth:25 - 26.5 Feet Tested By:Kevin Vandehey 4.5% Percent Percent by Sieve Size Passing Size Fraction Weight 3.0 in. (75.0) 100.0 Coarse Gravel 30.9 1.5 in. (37.5) 100.0 Fine Gravel 25.5 3/4 in. (19.0) 69.1 3/8 in. (9.5-mm) 53.5 Coarse Sand 11.3 No. 4 (4.75-mm) 43.6 Medium Sand 20.4 No. 10 (2.00-mm) 32.3 Fine Sand 8.6 No. 20 (.850-mm) 20.3 No. 40 (.425-mm) 11.9 Fines 3.3 No. 60 (.250-mm) 7.6 Total 100.0 No. 100 (.150-mm) 5.3 No. 200 (.075-mm) 3.3 LL - - PL - - Pl - - D10 0.35 D30 1.70 D60 14.00 D90 30.00 Cc 0.59 Cu 40.00 ASTM Classification Group Name:Poorly Graded Gravel with Sand Symbol:GP Gradation Analysis Summary Data Moisture Content (%) Job Name:Wyndstone Sample Location:MW-1 Job Number:1142-001-01 Sample Name:MW-1 30.0'-31.5' Date Tested:7/1/19 Depth:30 - 31.5 Feet Tested By:Kevin Vandehey 6.7% Percent Percent by Sieve Size Passing Size Fraction Weight 3.0 in. (75.0) 100.0 Coarse Gravel 7.9 1.5 in. (37.5) 100.0 Fine Gravel 47.8 3/4 in. (19.0) 92.1 3/8 in. (9.5-mm) 64.1 Coarse Sand 13.2 No. 4 (4.75-mm) 44.3 Medium Sand 17.9 No. 10 (2.00-mm) 31.1 Fine Sand 9.3 No. 20 (.850-mm) 19.9 No. 40 (.425-mm) 13.2 Fines 3.9 No. 60 (.250-mm) 9.4 Total 100.0 No. 100 (.150-mm) 6.5 No. 200 (.075-mm) 3.9 LL - - PL - - Pl - - D10 0.26 D30 1.80 D60 8.50 D90 18.00 Cc 1.47 Cu 32.69 ASTM Classification Group Name:Well Graded Gravel with Sand Symbol:GW Moisture Content (%) Gradation Analysis Summary Data Job Name:Wyndstone Sample Location: B-1 Job Number:1142-001-01 Sample Name: B-1 10.0'-11.5' Date Tested:7/1/19 Depth:10 - 11.5 Feet Tested By:Kevin Vandehey 3.9% Percent Percent by Sieve Size Passing Size Fraction Weight 3.0 in. (75.0)100.0 Coarse Gravel 15.0 1.5 in. (37.5)100.0 Fine Gravel 12.7 3/4 in. (19.0)85.0 3/8 in. (9.5-mm) 77.6 Coarse Sand 13.7 No. 4 (4.75-mm) 72.3 Medium Sand 31.1 No. 10 (2.00-mm) 58.7 Fine Sand 22.3 No. 20 (.850-mm) 42.5 No. 40 (.425-mm) 27.6 Fines 5.3 No. 60 (.250-mm) 17.2 Total 100.0 No. 100 (.150-mm) 10.6 No. 200 (.075-mm) 5.3 LL - - PL - - Pl - - D10 0.14 D30 0.47 D60 2.10 D90 25.00 Cc 0.75 Cu 15.00 ASTM Classification Group Name:Poorly Graded Sand with Gravel and Silt Symbol:SP-SM Moisture Content (%) Gradation Analysis Summary Data 01020304050607080901000.0010.010.11101001000Percent Passing by Weight Grain Size in MillimetersU.S. Standard Sieve SizeTP-2 0.5'-3.0'TP-2 3.0'-8.0'TP-5 0.5'-2.0'TP-5 2.0'-8.0'COBBLESGRAVELSILT OR CLAYSANDCOARSEMEDIUMFINECOARSEFINE3" 1.5" 3/4" 3/8" #4 #10 #20 #40 #60 #100 #200Graph 1Gradation Analysis ResultsWYNDSTONEYELM, WASHINGTON 01020304050607080901000.0010.010.11101001000Percent Passing by Weight Grain Size in MillimetersU.S. Standard Sieve SizeMW-1 25.0'-26.5'MW-1 30.0'-31.5'B-1 10.0'-11.5'COBBLESGRAVELSILT OR CLAYSANDCOARSEMEDIUMFINECOARSEFINE3" 1.5" 3/4" 3/8" #4 #10 #20 #40 #60 #100 #200Graph 2Gradation Analysis ResultsWYNDSTONEYELM, WASHINGTON Insight Geologic, Inc. ATTACHMENT C SIESMIC DESIGN PARAMETERS Hazards by Location 1 of 2 Search Information Coordinates:46.94455144795768, -122.62151451110839 Elevation:350 ft Timestamp:2019-07-10T17:29:07.126Z Hazard Type:Seismic Reference Document:IBC-2015 Risk Category:IV Site Class:D MCER Horizontal Response Spectrum Design Horizontal Response Spectrum Basic Parameters Name Value Description SS 1.251 MCER ground motion (period=0.2s) S1 0.499 MCER ground motion (period=1.0s) SMS 1.251 Site-modified spectral acceleration value SM1 0.749 Site-modified spectral acceleration value SDS 0.834 Numeric seismic design value at 0.2s SA SD1 0.5 Numeric seismic design value at 1.0s SA 0 5 10 15 Period (s) 0.00 0.20 0.40 0.60 0.80 1.00 1.20 Sa(g) 0 5 10 15 Period (s) 0.00 0.20 0.40 0.60 0.80 Sa(g) 2 of 2 Insight Geologic, Inc. ATTACHMENT D REPORT LIMITATIONS AND GUIDELINES FOR USE Insight Geologic, Inc. Limitations ATTACHMENT D REPORT LIMITATIONS AND GUIDELINES FOR USE1 This attachment provides information to help you manage your risks with respect to the use of this report. GEOTECHNICAL SERVICES ARE PERFORMED FOR SPECIFIC PURPOSES, PERSONS AND PROJECTS This report has been prepared for the exclusive use of C & E Developments LLC (Client) and their authorized agents. This report may be made available to regulatory agencies for review. This report is not intended for use by others, and the information contained herein is not applicable to other sites. Insight Geologic Inc. structures our services to meet the specific needs of our clients. For example, a geotechnical or geologic study conducted for a civil engineer or architect may not fulfill the needs of a construction contractor or even another civil engineer or architect that are involved in the same project. Because each geotechnical or geologic study is unique, each geotechnical engineering or geologic report is unique, prepared solely for the specific client and project site. Our report is prepared for the exclusive use of our Client. No other party may rely on the product of our services unless we agree in advance to such reliance in writing. This is to provide our firm with reasonable protection against open- ended liability claims by third parties with whom there would otherwise be no contractual limits to their actions. Within the limitations of scope, schedule and budget, our services have been executed in accordance with our Agreement with the Client and generally accepted geotechnical practices in this area at the time this report was prepared. This report should not be applied for any purpose or project except the one originally contemplated. A GEOTECHNICAL ENGINEERING OR GEOLOGIC REPORT IS BASED ON A UNIQUE SET OF PROJECT-SPECIFIC FACTORS Insight Geologic, Inc. considered a number of unique, project-specific factors when establishing the scope of services for this project and report. Unless Insight Geologic specifically indicates otherwise, do not rely on this report if it was:  not prepared for you,  not prepared for your project,  not prepared for the specific site explored, or  completed before important project changes were made. For example, changes that can affect the applicability of this report include those that affect:  the function of the proposed structure;  elevation, configuration, location, orientation or weight of the proposed structure;  composition of the design team; or  project ownership. If important changes are made after the date of this report, Insight Geologic should be given the opportunity to review our interpretations and recommendations and provide written modifications or confirmation, as appropriate. 1 Developed based on material provided by ASFE, Professional Firms Practicing in the Geosciences; www.asfe.org . Insight Geologic, Inc. Limitations SUBSURFACE CONDITIONS CAN CHANGE This geotechnical or geologic report is based on conditions that existed at the time the study was performed. The findings and conclusions of this report may be affected by the passage of time, by manmade events such as construction on or adjacent to the site, or by natural events such as floods, earthquakes, slope instability or ground water fluctuations. Always contact Insight Geologic before applying a report to determine if it remains applicable. MOST GEOTECHNICAL AND GEOLOGIC FINDINGS ARE PROFESSIONAL OPINIONS Our interpretations of subsurface conditions are based on field observations from widely spaced sampling locations at the site. Site exploration identifies subsurface conditions only at those points where subsurface tests are conducted or samples are taken. Insight Geologic reviewed field and laboratory data and then applied our professional judgment to render an opinion about subsurface conditions throughout the site. Actual subsurface conditions may differ, sometimes significantly, from those indicated in this report. Our report, conclusions and interpretations should not be construed as a warranty of the subsurface conditions. GEOTECHNICAL ENGINEERING REPORT RECOMMENDATIONS ARE NOT FINAL Do not over-rely on the preliminary construction recommendations included in this report. These recommendations are not final, because they were developed principally from Insight Geologic’s professional judgment and opinion. Insight Geologic’s recommendations can be finalized only by observing actual subsurface conditions revealed during construction. Insight Geologic cannot assume responsibility or liability for this report's recommendations if we do not perform construction observation. Sufficient monitoring, testing and consultation by Insight Geologic should be provided during construction to confirm that the conditions encountered are consistent with those indicated by the explorations, to provide recommendations for design changes should the conditions revealed during the work differ from those anticipated, and to evaluate whether or not earthwork activities are completed in accordance with our recommendations. Retaining Insight Geologic for construction observation for this project is the most effective method of managing the risks associated with unanticipated conditions. A GEOTECHNICAL ENGINEERING OR GEOLOGIC REPORT COULD BE SUBJECT TO MISINTERPRETATION Misinterpretation of this report by other design team members can result in costly problems. You could lower that risk by having Insight Geologic confer with appropriate members of the design team after submitting the report. Also retain Insight Geologic to review pertinent elements of the design team's plans and specifications. Contractors can also misinterpret a geotechnical engineering or geologic report. Reduce that risk by having Insight Geologic participate in pre-bid and pre-construction conferences, and by providing construction observation. DO NOT REDRAW THE EXPLORATION LOGS Geotechnical engineers and geologists prepare final boring and testing logs based upon their interpretation of field logs and laboratory data. To prevent errors or omissions, the logs included in a Insight Geologic, Inc. Limitations geotechnical engineering or geologic report should never be redrawn for inclusion in architectural or other design drawings. Only photographic or electronic reproduction is acceptable, but recognize that separating logs from the report can elevate risk. GIVE CONTRACTORS A COMPLETE REPORT AND GUIDANCE Some owners and design professionals believe they can make contractors liable for unanticipated subsurface conditions by limiting what they provide for bid preparation. To help prevent costly problems, give contractors the complete geotechnical engineering or geologic report, but preface it with a clearly written letter of transmittal. In that letter, advise contractors that the report was not prepared for purposes of bid development and that the report's accuracy is limited; encourage them to confer with Insight Geologic and/or to conduct additional study to obtain the specific types of information they need or prefer. A pre-bid conference can also be valuable. Be sure contractors have sufficient time to perform additional study. Only then might an owner be in a position to give contractors the best information available, while requiring them to at least share the financial responsibilities stemming from unanticipated conditions. Further, a contingency for unanticipated conditions should be included in your project budget and schedule. CONTRACTORS ARE RESPONSIBLE FOR SITE SAFETY ON THEIR OWN CONSTRUCTION PROJECTS Our geotechnical recommendations are not intended to direct the contractor’s procedures, methods, schedule or management of the work site. The contractor is solely responsible for job site safety and for managing construction operations to minimize risks to on-site personnel and to adjacent properties. READ THESE PROVISIONS CLOSELY Some clients, design professionals and contractors may not recognize that the geoscience practices (geotechnical engineering or geology) are far less exact than other engineering and natural science disciplines. This lack of understanding can create unrealistic expectations that could lead to disappointments, claims and disputes. Insight Geologic includes these explanatory “limitations” provisions in our reports to help reduce such risks. Please confer with Insight Geologic if you are unclear how these “Report Limitations and Guidelines for Use” apply to your project or site. GEOTECHNICAL, GEOLOGIC AND ENVIRONMENTAL REPORTS SHOULD NOT BE INTERCHANGED The equipment, techniques and personnel used to perform an environmental study differ significantly from those used to perform a geotechnical or geologic study and vice versa. For that reason, a geotechnical engineering or geologic report does not usually relate any environmental findings, conclusions or recommendations; e.g., about the likelihood of encountering underground storage tanks or regulated contaminants. Similarly, environmental reports are not used to address geotechnical or geologic concerns regarding a specific project. TO: Casey Peterson FROM: William Halbert, L.E.G., L.Hg. DATE: July 26, 2019 PROJECT: 1142-001-02 Wyndstone Residential SUBJECT: Supplemental Infiltration Rate Evaluation At the request of Peterson Brothers LLC, we have conducted a supplemental evaluation for the proposed stormwater infiltration at the Wyndstone multi-family residential development to be located 15025 Tahoma Boulevard SE in Yelm, Washington. Our previous investigations and evaluation of design stormwater infiltration rates for the project, using the “Detailed Approach” as described in the Department of Ecology’s 2014 Stormwater Management Manual for Western Washington (2014 Manual), as adopted by the City of Yelm, produced artificially low infiltration rates for the site based on similar sites in the area in similar soils. It was decided that we also run a full-scale Pilot Infiltration Test (PIT) as a more realistic method of determining the infiltration rate of the soil. On July 24, 2019, we completed two stormwater infiltration rate evaluations in general accordance with the 2014 Manual consisting of full-scale PITs. The PITs were performed at the north and south side of the site at a depth of 5 feet below ground surface. For the PITs, a 10-foot by 10-foot area was excavated to a depth of about 5 feet below ground surface. The PIT located on the north side of the site was located within the area of the proposed stormwater infiltration gallery. A second PIT was excavated on the south side of the site for comparison purposes. The base of the excavations correlated to the approximate elevation of the base of the proposed stormwater infiltration gallery. The soils exposed in the base of the excavations consisted of fine to course gravel and cobbles with sand and trace silt, which was consistent with our previous observations. Water was added to the excavations using a water tuck provided by Peterson Brothers LLC to saturate the underlying soils. Datalogging pressure transducers were placed in the bottom of the excavations to provide a constant record of the water level during the PITs. Despite adding approximately 4,000 gallons of water to PIT-1 at the maximum rate available to the water truck, we were unable to develop standing water in the base of the PIT excavation. Water levels were able to be maintained in in PIT-2 until the water truck was drained and then the excavation drained in approximately 15 minutes. The water levels over time for PIT-1 and PIT-2 are shown in Figure 1 and Figure 2, below. The initial infiltration rate was calculated using the fall of the water level in inches over time. MEMORANDUM 1015 East 4th Avenue Olympia, Washington 98506 Telephone: (360) 754-2128 Fax: (360) 754-9299 Wyndstone Supplemental July 26, 2019 Page 2 Figure 1. PIT-1 Hydrograph Figure 2. PIT-2 Hydrograph 0 0.1 0.2 0.3 0.4 0.5 8:38 AM 8:45 AM 8:52 AM 9:00 AM 9:07 AMWater Depth (Feet)Time 0 0.5 1 1.5 2 2.5 9:36 AM 9:50 AM 10:04 AM 10:19 AM 10:33 AM 10:48 AM 11:02 AM 11:16 AMWater Depth (Feet)Time Wyndstone Supplemental July 26, 2019 Page 3 Based on the “Simple Approach” as described in the 2014 Manual, we then applied the appropriate correction factors to the initial infiltration rates which generated a design infiltration rate of between 132 and 104 inches per hour. However, as the site has a contributing area of larger than 1 acre the 2014 Manual recommends the use of the “Detailed Approach” to determine the design infiltration rate. Using the additional site-specific correction factors and depth to groundwater utilized in the Detailed Approach, the design infiltration rate is between 12.2 and 8.3 inches per hour. Based on the gravel and cobbly nature of the site and that the depth to groundwater is greater than 30 feet below ground surface, it is our opinion that the reduction in infiltration rate generated by the Detailed Approach is overly conservative as groundwater mounding is unlikely to develop in the gravel soils at the site. As a result, we have generated a discretionary correction factor of 0.4 that takes into account the corrections presented on the Detailed Approach while reducing the correction that is based on potential mounding effects of the groundwater table. Correction values are shown in Table 1, below. Our final design infiltration rate based on these revised correction values are between 32 and 21 inches per hour. Please note that this design infiltration rate is based on current site conditions and may be adjusted depending on significant increases in groundwater elevations during the winter groundwater monitoring period. Table 1. Design Infiltration Rate Calculation PIT Initial Infiltration Rate (in./hr.) Testing Methodology Correction Factor Site Variability Correction Factor Plugging Correction Factor Discretionary Correction Factor Design Infiltration Rate (in./hr.) PIT-1 132.8 0.75 0.9 0.9 0.4 32.2 PIT-2 86 0.75 0.9 0.9 0.4 20.9 We trust this meets your current requirements. Please contact us if you have questions regarding our testing. APPENDIX E Temporary Sediment Pond Calculations Sediment Pond Sizing Calculations Required Surface Area SA = 2080 *Q2 where; Q2 = 1.16-cfs SA = 2080 *1.16-cfs = 2,413-sq.ft. required; 2,700-sq.ft. provided Dewatering Orifice Ao = [As(2h)0.5]/[0.6x3600Tg0.5] D = 13.54*(Ao) 0.5 where; Ao = orifice area (square feet) As = pond surface area = 2,700-sq.ft. h = head of water above orifice from Figure 4.2.21 (height of riser in feet) = 0.30-feet T = dewatering time (24 hours) g = acceleration of gravity (32.2 feet/second2) Ao = [2,700-sq.ft.*(2*0.30-ft)0.5]/[0.6*3600*24-hr*(32.2ft/s2)0.5] = 0.0071-sq.ft. D = 13.54*(0.0071-sq.ft.) 0.5 = 1.142-inches; therefore, use 1.125-inches provided APPENDIX F Operations and Maintenance Manual OPERATION AND MAINTENANCE MANUAL FOR DRAINAGE FACILITIES FOR Wyndstone Yelm, Washington March 2020 Prepared for: C & E Developments, LLC PO Box 2983 Yelm, WA 98597 Prepared by: Daniel Smith, P.E., Project Manager Approved By: Craig Deaver, Principal REPORT #06164 F-1 Operation and Maintenance Information Project Information Address: 15025 Tahoma Blvd SE Yelm, WA 98597 Tax Parcel Numbers: 21724420300 Ownership: C & E Developments, LLC Maintenance Responsibility: C & E Developments, LLC Record Keeping: The Operation and Maintenance Manual shall be made available for inspection by the City of Yelm and shall be kept in the manager’s office. System Description The Wyndstone project consists of 75 multifamily units across four building situated on parcel # 21724420300 totaling approximately 4.67 acres. The project is to be constructed in two separate phases with Buildings 1 and 2 with associated utilities and parking constructed in Phase I, and Buildings 3 and 4 with the remaining utilities and parking constructed in Phase II. A new public roadway extension from Tahoma Blvd SE is proposed as part of Phase I and will extend the full length of the eastern boundary line. An infiltration trench is proposed to fully infiltrate runoff from both phases with a FloGard Perk Filter vault upstream that provides basic runoff treatment. These facilities are placed between Building 1 and Tahoma Blvd SE. Long-term maintenance shall be done in accordance with Attachment “A” and as follows: All conveyance systems shall be inspected for sediment and blockages on yearly basis or after large storm events. The main contributor of sediment to the storm system are the asphalt pavement surfaces. Therefore, sweeping of the asphalt pavement surfaces through the use of a street sweeper twice a year should help to prevent sediments from F-2 clogging the porous in the asphalt and entering the storm system. The debris collected shall be disposed of in an approved method. Long-term maintenance of the storm drainage system will be the responsibility of the current property owner and shall be completed in accordance with Attachment “A” and the guidelines listed above. The average annual cost for maintenance is approximated to be $5,000.00. Vegetation Management Native species affecting the storm drainage system are not applicable for this project. Maintenance checklists on the following pages and instructions listed above address appropriate maintenance requirements. F-3 Instructions for Use of Maintenance Checklists The following pages contain maintenance needs for most of the components that are part of your drainage system, as well as for some components that you may not have. Let the City know if there are any components that are missing from these pages. Ignore the requirements that do not apply to your system. You should plan to complete a checklist for all system components on the following schedule: 1. Monthly from November through April. 2. Once in late summer (preferably in September). 3. After any major storm (use 1-inch in 24-hours as a guideline), items marked as “regularly” or “after rain event”. Using photocopies of the checklist pages, check off the problems that you looked for each time you did an inspection. Add comments on problems found and actions taken. Keep these “checked” sheets in your files. Some items do not need to be looked at every time an inspection is done. Use the suggested frequency at the left of each item as a guideline for your inspection. Maintenance Checklists See the following pages for these attachments. F-4 REQUIRED ACTIONS: The following actions shall be taken to ensure that pollution generated on site shall be minimized: 1. Parking lots shall be swept when necessary to remove debris and, at a minimum, twice a year. Use of newer model high-velocity vacuum sweepers is recommended, as they are more effective in removing the more harmful smaller particles from paved surfaces. 2 No activities shall be conducted onsite that are likely to result in short-term high- concentration discharge of pollution to the stormwater system. Such activities may include, but are not limited to; vehicle washing, vehicle maintenance, and cleaning of equipment used in the periodic maintenance of buildings and paved surfaces. 3. Employees shall receive basic instruction regarding the control of pollution from commercial operations. Contact the City of Yelm or Department of Ecology for assistance in completing this task. F-5 ATTACHMENT “A” MAINTENANCE PROGRAM COVER SHEET FOR CITY OF YELM Inspection Period: Number of Sheets Attached: Date Inspected: Name of Inspector: Inspector’s Signature: F-6 F-7 F-8 F-9 F-10 Comments: