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10160 - Justman Farm SWPPP - 20241005 Larson & Associates surveyors, engineers and planners 9027 Pacific Avenue, Suite 4 Tacoma, WA 98444 STORMWATER POLLUTION PREVENTION PLAN PROPONENT: C&E DEVELOPMENTS, LLC P.O. BOX 2983 YELM, WA 98597 CONTACT: ERIC PETERSON PHONE: (253) 278-0343 PREPARED BY: Larson & Associates surveyors, engineers and planners 9027 Pacific Avenue, Suite 4 Tacoma, WA 98444 (253) 474-3404 9/5/2024 Page 1 of 140 PROJECT ENGINEER'S CERTIFICATION.......................................................................................................... 1 STORMWATER POLLUTION PREVENTION PLAN SECTION 1 - CONSTRUCTION STORMWATER POLLUTION PREVENTION ELEMENTS ......................2-11 SECTION 2 - PROJECT DESCRIPTION .......................................................................................................... 11-12 SECTION 3 - EXISTING SITE CONDITIONS ...................................................................................................... 12 SECTION 4 - ADJACENT AREAS ........................................................................................................................ 12 SECTION 5 - CRITICAL AREAS .......................................................................................................................... 12 SECTION 6 - SOILS .......................................................................................................................................... 12-13 SECTION 7 - EROSION PROBLEM AREAS ........................................................................................................ 13 SECTION 8 - CONSTRUCTION PHASING ..................................................................................................... 13-14 SECTION 9 - CONSTRUCTION SCHEDULE ...................................................................................................... 14 SECTION 10 - FINANCIAL/OWNERSHIP RESPONSIBILITIES ....................................................................... 14 SECTION 11 - ENGINEERING CALCULATIONS ......................................................................................... 14-18 SECTION 12 - EROSION CONTROL SPECIALIST ............................................................................................. 18 APPENDIX "A" .............................................................. STORMWATER POLLUTION PREVENTION BMPS APPENDIX "B" .................................................................................................................................. FEMA MAP APPENDIX "C" .............................................................. WETLAND DELINEATION AND RATING REPORT APPENDIX "D" ......................................................................................................................... NRCS SOIL MAP Page 2 of 140 I hereby state that this Stormwater Pollution Prevention Plan for JUSTMAN FARM has been prepared by me or under my supervision and meets the standard of care and expertise which is usual and customary in this community for professional engineers. I understand that Washington State and City of Yelm does not and will not assume liability for the sufficiency, suitability, or performance of drainage facilities prepared by me. 9/5/2024 Grant J. Middleton, P.E. Page 3 of 140 SECTION 1 – CONSTRUCTION STORMWATER POLLUTION PREVENTION ELEMENTS Stormwater pollution prevention will be maintained during the construction of this site by incorporating standard erosion control methods such as a temporary construction entrance and mirafi siltation fences. The following devices will be used to trap sediment from the cleared areas and prevent it from leaving the site. A construction entrance will be installed at the entrance to the site to keep sediment from being tracked out of the site and onto the County roads. Mirafi silt fences will be installed along the perimeter to prevent sediment runoff from exiting the project limits. The following general Washington State Dept. of Ecology Construction Stormwater Pollution Prevention Elements shall be upheld at all times during the construction process. Please reference the Best Management Practices (BMPs) in Appendix A of this report. Element #1: Preserve Vegetation/Mark Clearing Limits • Prior to beginning land disturbing activities, including clearing and grading, clearly mark all clearing limits, sensitive areas and their buffers, and trees that are to be preserved within the construction area. These shall be marked, both in the field and on the plans, to prevent damage and offsite impacts. • The duff layer, native topsoil, and natural vegetation shall be retained in an undisturbed state to the maximum degree practicable. If it is not practical to retain the native topsoil or duff layer in place, then stockpile it onsite or at an approved location, cover it to prevent erosion, and replace it immediately when site disturbance is complete. See SOIL PRESERVATION AND AMENDMENT NOTES on the site development plans. • Plastic, metal, or stake wire fence may be used to mark the clearing limits. • Suggested BMPs: - BMP C103: High Visibility Plastic or Metal Fence - BMP C233: Silt Fence Element #2: Establish Construction Access • Construction vehicle access and exit shall be limited to one route, if possible. • Access points shall be stabilized with a pad of quarry spalls, crushed rock or other equivalent BMP, to minimize the tracking of sediment onto public roads. • Wheel wash or tire baths should be located on site, if the stabilized construction entrance is not effective in preventing sediment from being tracked onto public roads. Page 4 of 140 • If sediment is tracked off site, public roads shall be cleaned thoroughly at the end of each day, or more frequently during wet weather. Sediment shall be removed from roads by shoveling or pickup sweeping and shall be transported to a controlled sediment disposal area. • Street washing is allowed only after sediment is removed in accordance with the above bullet. Street wash wastewater shall be controlled by pumping back on site or otherwise be prevented from discharging into systems tributary to waters of the state. • Suggested BMPs: - BMP C105: Stabilized Construction Entrance Element #3: Control Flow Rates • Protect properties and waterways downstream of the proposed development from erosion and the associated discharge of turbid waters due to increases in the velocity and peak volumetric flow rate of stormwater runoff from the project site. • Due to the native soil’s significant infiltration rate, it is the intent of the project storm drainage design to infiltrate 100% of the stormwater runoff with no surface discharge offsite. The site topography is also relatively flat, so very little, if any, stormwater runoff is expected to discharge offsite during construction. However, if necessary, flow control BMPs can be placed along the perimeter of the project, adjacent to the silt fence. • Suggested BMPs: - BMP C207: Check Dams Element #4: Install Sediment Controls • Install and maintain effective erosion controls and sediment controls to minimize the discharge of pollutants. • Construct sediment control BMPs as one of the first steps in grading. These BMPs shall be functional before other land disturbing activities take place. • Suggested BMPs: - BMP C233: Silt Fence Element #5: Stabilize Soils • Exposed and unworked soils shall be stabilized by application of effective BMPs that prevent erosion. Applicable BMPs include, but are not limited to: temporary and permanent seeding, sodding, mulching, plastic covering, the early application of gravel base on areas to be paved, and dust control. Page 5 of 140 • Soils must not remain exposed and unworked for more than the time periods set forth below to prevent erosion: - During the dry season (May 1 – Sept. 30): 7 days - During the wet season (October 1 – April 30): 2 days • Stabilize soils at the end of the shift before a holiday or weekend if needed based on the weather forecast. • Stabilize soil stockpiles from erosion, protected with sediment trapping measures, and where possible, locate away from storm drain inlets, waterways, and drainage channels. • Suggested BMPs: - BMP C120: Temporary and Permanent Seeding - BMP C121: Mulching - BMP C123: Plastic Covering - BMP C124: Sodding - BMP C125: Topsoiling/Composting - BMP C140: Dust Control Element #6: Protect Slopes • Construct cut-and-fill slopes in a manner to minimize erosion. • Divert offsite stormwater (run-on) or groundwater away from slopes and disturbed areas with interceptor dikes, pipes, and/or swales. Offsite stormwater must be managed separately from stormwater generated on the site. • At the top of slopes, collect drainage in pipe slope drains or protected channels to prevent erosion. • Provide drainage to remove groundwater intersecting the slope surface of exposed soil areas. • Place excavated material on the uphill side of trenches, consistent with safety and space considerations. • Place check dams at regular intervals within constructed channels that are cut down a slope. • Stabilize soils on slopes, as specified in Element #5 above. • Suggested BMPs: - BMP C120: Temporary and Permanent Seeding - BMP C121: Mulching - BMP C200: Interceptor Dike and Swale - BMP C207: Check Dams Page 6 of 140 Element #7: Protect Drain Inlets • Protect all storm drain inlets made operable during construction, including offsite inlets adjacent to the project site, so that stormwater runoff does not enter the conveyance system without first being filtered or treated to remove sediment. • Clean or remove and replace inlet protection devices when sediment has filled one- third of the available storage (unless a different standard is specified by the product manufacturer). • Inlets shall be inspected weekly at a minimum and daily during storm events. • Keep all approach roads clean. Sediment and street wash wastewater shall be controlled as specified above in Element #2. • Suggested BMPs: - BMP C220: Storm Drain Inlet Protection Element #8: Stabilize Channels and Outlets • Provide stabilization, including armoring material, adequate to prevent erosion of outlets, adjacent streambanks, slopes, and downstream reaches at the outlets of all conveyance systems. • The preferred method for stabilizing channels is to completely line the channel with a blanket product first, then add check dams as necessary to function as an anchor and to slow the flow of water. • Suggested BMPs: - BMP C207: Check Dams Element #9: Control Pollutants • Handle and dispose of all pollutants, including waste materials and demolition debris that occurs onsite in a manner that does not cause contamination of stormwater. Woody debris may be chopped and spread onsite. • Provide cover, containment, and protection from vandalism for all chemicals, liquid products, petroleum products, and other materials that have the potential to pose a threat to human health or the environment. Onsite fueling tanks must include secondary containment, i.e. – placing tanks or containers within an impervious structure capable of containing 110% of the volume contained in the largest tank within the containment structure. Double-walled tanks do not require additional secondary containment. Page 7 of 140 • Conduct maintenance, fueling, and repair of heavy equipment and vehicles using spill prevention and control measures. Clean contaminated surfaces immediately following any spill incident. • Conduct oil changes, hydraulic system drain down, solvent and de-greasing cleaning operations, fuel tank drain down and removal, and other activities which may result in discharge or spillage of pollutants to the ground or into stormwater runoff using spill prevention measures, such as drip pans. • Discharge wheel wash or tire bath wastewater shall be discharged to a separate onsite treatment system that prevents discharge to surface water, such as closed-loop recirculation or to the sanitary sewer. For discharges to the sanitary sewer, permits must be obtained from the County Industrial Pretreatment Program at (253) 798-3013. • Apply fertilizers and pesticides in a manner and at application rates that will not result in loss of chemical to stormwater runoff. Follow manufacturers’ label requirements for application rates and procedures. • Use BMPs to prevent contamination of stormwater runoff by pH-modifying sources. The sources for this contamination include, but are not limited to: bulk cement, cement kiln dust, fly ash, new concrete washing and curing waters, waste streams generated from concrete grinding and sawing, exposed aggregate processes, dewatering concrete vaults, concrete pumping and mixer washout waters. Adjust the pH of stormwater if necessary, to prevent violations of water quality standards. • Obtain written approval from Ecology before using chemical treatment, other than CO2 or dry ice to adjust pH. • Wheel wash or tire bath wastewater should not include wastewater from concrete washout areas. • Clean contaminated surfaces immediately following any discharge or spill incident. Emergency repairs may be performed onsite using temporary plastic placed beneath and, if raining, over the vehicle. • Suggested BMPs: - BMP C151: Concrete Handling - BMP C153: Material Delivery, Storage and Containment Element #10: Control Dewatering • Discharge foundation, vault, and trench dewatering water, which have characteristics similar to stormwater runoff at the site, into a controlled conveyance system before discharging to a sediment trap or sediment pond. • Channels must be stabilized, as specified in Element #8. Page 8 of 140 • Discharging sediment-laden (muddy) water into waters of the State likely constitutes violation of water quality standards for turbidity. The easiest way to avoid discharging muddy water is through infiltration and preserving vegetation. • Suggested BMPs: - BMP C203: Water Bars - BMP C236: Vegetative Filtration Element #11: Maintain BMPs • Maintain and repair all temporary and permanent Construction SWPPP BMPs as needed to ensure continued performance of their intended function in accordance with BMP specifications. • Remove all temporary Construction SWPPP BMPs within 30 days after achieving final site stabilization or after the temporary BMPs are no longer needed. • Provide protection to all BMPs installed for the permanent control of stormwater from sediment and compaction. All BMPs that are to remain in place following completion of construction shall be examined and placed in full operating conditions. If sediment enters the BMPs during construction, it shall be removed and the facility shall be returned to the conditions specified in the site development plans. • Suggested BMPs: - BMP C160: Certified Erosion and Sediment Control Lead Element #12: Manage the Project • Phase development projects to the maximum degree practicable and take into account seasonal work limitations. • Inspection and Monitoring - Inspect, maintain, and repair all BMPs as needed to ensure continued performance of their intended function. Conduct site inspections and monitoring in accordance with all applicable county and Construction Stormwater General Permit requirements. • Maintaining an updated Construction SWPPP – Maintain, update, and implement the Construction SWPPP in accordance with the Construction Stormwater General Permit requirements and the requirements outlined in this Element (#12). • Because this project will disturb more than 1 acre, site inspections must be conducted by a Certified Erosion and Sediment Control Lead (CESCL). By the initiation of construction, the Construction SWPPP must identify the CESCL or inspector, who shall be present onsite or on-call at all times. Page 9 of 140 • Monitoring Requirements – the following monitoring requirements to be performed by the CECSL conform to the requirements of the Construction Stormwater General Permit (conditions referenced herein): The primary monitoring requirements are summarized in Table 3 (below): Table 3. Summary of Monitoring Requirements1 Size of Soils Disturbance2 Weekly Site Inspections Weekly Sampling w/ Turbidity Meter Weekly Sampling w/ Transparency Tube Weekly pH sampling3 Sites which disturb less than 1 acre Required Not Required Not Required Not Required Sites which disturb 1 acre or more, but less than 5 acres Required Sampling Required – either method4 Required Sites which disturb 5 acres or more Required Required Not Required5 Required 1 Additional monitoring requirements may apply for: 1) discharges to 303(d) listed waterbodies and waterbodies with applicable TMDLs for turbidity, fine sediment, high pH, or phosphorus – see Condition S8; and 2) sites required to perform additional monitoring by Ecology order – see Condition G13. 2 Soil disturbance is calculated by adding together all areas affected by construction activity. Construction Activity means clearing, grading, excavation, and any other activity which disturbs the surface of the land, including ingress/egress from the site. 3 Beginning October 1, 2006, if construction activity involves significant concrete work or the use of engineered soils, and stormwater from the affected area drains to a stormwater collection system or other surface water, the Permittee shall conduct pH sampling in accordance with Condition S4.D. 4 Beginning October 1, 2008, sites with one or more acres, but less than 5 acres of soil disturbance, shall conduct turbidity or transparency sampling in accordance with Condition S4.C. 5 Beginning October 1, 2006, sites greater than or equal to 5 acres of soil disturbance shall conduct turbidity sampling using a turbidity meter in accordance with Condition S4.C. A. Site Log Book The CESCL shall maintain a site log book that contains a record of the implementation of the SWPPP and other permit requirements including the installation and maintenance of BMPs, site inspections, and stormwater monitoring. B. Site Inspections 1. Site inspections shall include all areas disturbed by construction activities, all BMPs, and all stormwater discharge points. Stormwater shall be visually examined for the presence of suspended sediment, turbidity, discoloration, and oil sheen. Inspectors shall evaluate the effectiveness of BMPs and Page 10 of 140 determine if it is necessary to install, maintain, or repair BMPs to improve the quality of stormwater discharges. Based on the results of the inspection, the Permittee shall correct the problems identified as follows: a. Review the SWPPP for compliance with Condition S9 and make appropriate revisions within 7 days of the inspection; and b. Fully implement and maintain appropriate source control and/or treatment BMPs as soon as possible, but no later than 10 days of the inspection; and c. Document BMP implementation and maintenance in the site log book. 2. The site inspections shall be conducted at least once every calendar week and within 24 hours of any discharge from the site. The inspection frequency for temporarily stabilized, inactive sites may be reduced to once every calendar month. 3. Site inspections shall be conducted by a person who is knowledgeable in the principles and practices of erosion and sediment control. The inspector shall have the skills to: a. Assess the site conditions and construction activities that could impact the quality of stormwater, and b. Assess the effectiveness of erosion and sediment control measures used to control the quality of stormwater discharges. 4. Beginning October 1, 2006, construction sites one acre or larger that discharge stormwater to surface waters of the state, shall have site inspections conducted by a Certified Erosion and Sediment Control Lead (CESCL). The CESCL shall be identified in the SWPPP and shall be present on-site or on- call at all times. Certification shall be obtained through an approved erosion and sediment control training program that meets the minimum training standards established by Ecology (see BMP C160 in the Manual). 5. The inspector shall summarize the results of each inspection in an inspection report or checklist and be entered into, or attached to, the site log book. At a minimum, each inspection report or checklist shall include: a. Inspection date and time. b. Weather information: general conditions during inspection and approximate amount of precipitation since the last inspection, and within the last 24 hours. Page 11 of 140 c. A summary or list of all BMPs which have been implemented, including observations of all erosion/sediment control structures or practices. d. The following shall be noted: i. locations of BMPs inspected, ii. locations of BMPs that need maintenance, iii. the reason maintenance is needed, iv. locations of BMPs that failed to operate as designed or intended, and v. locations where additional or different BMPs are needed, and the reason(s) why. e. A description of stormwater discharged from the site. The inspector shall note the presence of suspended sediment, turbid water, discoloration, and/or oil sheen, as applicable. f. Any water quality monitoring performed during inspection. g. General comments and notes, including a brief description of any BMP repairs, maintenance or installations made as a result of the inspection. h. A statement that, in the judgment of the person conducting the site inspection, the site is either in compliance or out of compliance with the terms and conditions of the SWPPP and the permit. If the site inspection indicates that the site is out of compliance, the inspection report shall include a summary of the remedial actions required to bring the site back into compliance, as well as a schedule of implementation. i. Name, title, and signature of the person conducting site inspection; and the following statement: “I certify that this report is true, accurate, and complete, to the best of my knowledge and belief”. Element #13: Protect Low Impact Development BMPs • To ensure that LID stormwater facilities and BMPs will be fully functional after construction, it is important to protect these BMPs during construction activities. Protecting native soil and vegetation, minimizing soil compaction, and retaining the hydrologic function of LID BMPs during the site preparation and construction phases are some of the most important practices during the development process. • Limit construction activity in areas designated for LID BMPs. Page 12 of 140 • Limit clearing and grading activities during heavy rainfall seasons. • Minimize the amount and time that graded areas are left exposed. • Protect native topsoil during the construction phase, and reuse onsite. Cover small stockpiles with weed barrier material that sheds moisture yet allows air transmission. Large stockpiles may need to be seeded and/or mulched. • Provide proper soil amendments with native topsoil where necessary. • Suggested BMPs: - BMP C103: High Visibility Fence - BMP C200: Interceptor Dike and Swale - BMP C207: Check Dams - BMP C233: Silt Fence SECTION 2 – PROJECT DESCRIPTION The proposed Justman Farm project is located in the NW 1/4 of the SW 1/4 of Section 29, Township 17 North, Range 2 East of the Willamette Meridian in Yelm, Washington. Parcel number is TPN 64303200600, and the area of the lot is 9.37 ac. The project consists of providing a landscaping wall and grading the site. SECTION 3 – EXISTING SITE CONDITIONS The project parcel is located on the south side of SR 507 at the eastern edge of the City of Yelm’s city limits. The property is currently zoned C-2 Heavy Commercial according to the City’s current Zoning Map. Surrounding properties consist of large tract farms to the south, west and east. According to FEMA Flood Map Service Center Flood Map 53067C0362F, flood Zone X with established base flood elevation 349.7 – 349.9 feet (NAVD 88) located within floodway of Yelm Creek located west of the property. Refer to Appendix “B” for additional information. SECTION 4 – ADJACENT AREAS Surrounding properties consist of large tract farms to the south, west and east. Commercial properties are located across SR 507 to the north. SECTION 5 – CRITICAL AREAS Yelm Creek wetland system runs along the western edge of the parcel. Refer to Appendix C for Wetland Delineation and Rating Report completed by SCJ Alliance Consulting Services on December 2017. SECTION 6 - SOILS The National Resources and Conservation Services (NRCS) describes on-site soils primarily as Spanaway gravelly sandy loam, 0 to 3 percent slopes. See Appendix D for NRCS soil mapping. Page 13 of 140 SECTION 7 – EROSION PROBLEM AREAS To the best of our knowledge, there are no erosion problem areas on or in the direct vicinity of the project site. SECTION 8 – CONSTRUCTION PHASING The proposed construction sequence will be as follows: 1. Contact the City of Yelm inspector to schedule the pre-construction meeting. 2. Clearly flag all limits of clearing and grading per the approved site development plans. 3. Install a temporary construction entrance as shown and per the notes and details. 4. Install temporary filter fabric (silt) fences as shown and per the notes and details. 5. Construct the temporary sediment pond as shown and per the notes and details. 6. Install the temporary interceptor swales and rock check dams as shown and per the notes and details. 7. Clear and grade site per the approved plans, stockpiling duff and topsoil per the soil preservation and amendment notes. 8. Hydroseed and/or mulch slopes and other exposed areas immediately after grading is completed as outlined in “erosion control notes”. SECTION 9 – CONSTRUCTION SCHEDULE Construction of this project will likely begin in the Fall of 2024, and will follow the above construction sequence. During the wet season from October 1 through March 31, no soils shall remain exposed and unworked for more than 2 days at a time. SECTION 10 – FINANCIAL/OWNERSHIP RESPONSIBLITIES The property owner responsible for the initiation of any necessary bonds and/or other financial securities is: C&E DEVELOPMENTS, LLC P.O. BOX 2983 YELM, WA 98597 CONTACT: ERIC PETERSON PHONE: (253) 278-0343 Page 14 of 140 SECTION 11 – ENGINEERING CALCULATIONS None. SECTION 12 – EROSION CONTROL SPECIALIST No Certified Erosion and Sediment Control Lead (CESCL) has been appointed at this time. Once one is established, he/she will be reported to the City of Yelm and WA State Department of Ecology. End of Report Page 15 of 140 APPENDIX “A” STORMWATER POLLUTION PREVENTION BMPs Page 16 of 140 permitting authority. These should not be disturbed and must protected with sediment con- trol BMPs to prevent impacts. The local permitting authority may expand the buffer widths  temporarily to allow the use of the expanded area for removal of sediment.  l Vegetative Buffer Zones - areas that may be identified in undisturbed vegetation areas or  managed vegetation areas that are outside any Designated Critical Area Buffer. They may  be utilized to provide an additional sediment control area and/or reduce runoff velocities. If  being used for preservation of natural vegetation, they should be arranged in clumps or  strips. They can be used to protect natural swales and incorporated into the natural land- scaping area. Design and Installation Specifications  l Preserving natural vegetation or plantings in clumps, blocks, or strips is generally the easi- est and most successful method.  l Leave all unstable steep slopes in natural vegetation.  l Mark clearing limits and keep all equipment and construction debris out of the natural areas  and buffer zones. Steel construction fencing is the most effective method to protect sens- itive areas and buffers. Alternatively, wire-backed silt fence on steel posts is marginally  effective. Flagging alone is typically not effective.  l Keep all excavations outside the dripline of trees and shrubs.  l Do not push debris or extra soil into the buffer zone area because it will cause damage by  burying and smothering vegetation.  l Vegetative buffer zones for streams, lakes or other waterways shall be established by the  local permitting authority or other state or federal permits or approvals. Maintenance Standards Inspect the area frequently to make sure flagging remains in place and the area remains undis- turbed. Replace all damaged flagging immediately. Remove all materials located in the buffer  area that may impede the ability of the vegetation to act as a filter. BMP C103: High-Visibility Fence Purpose High-visibility fencing is intended to:  l Restrict clearing to approved limits.  l Prevent disturbance of sensitive areas, their buffers, and other areas required to be left  undisturbed.  l Limit construction traffic to designated construction entrances, exits, or internal roads.  l Protect areas where marking with survey tape may not provide adequate protection. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 315Page 17 of 140 Conditions of Use To establish clearing limits, plastic, fabric, or metal fence may be used:  l At the boundary of sensitive areas, their buffers, and other areas required to be left  uncleared.  l As necessary to control vehicle access to and on the site. Design and Installation Specifications High-visibility plastic fence shall be composed of a high-density polyethylene (HDPE) material  and shall be at least four feet in height. Posts for the fencing shall be steel or wood and placed  every 6 feet on center (maximum) or as needed to ensure rigidity. The fencing shall be fastened to  the post every six inches with a polyethylene tie. On long continuous lengths of fencing, a tension  wire or rope shall be used as a top stringer to prevent sagging between posts. The fence color  shall be high-visibility orange. The fence tensile strength shall be 360 lbs/ft using the ASTM  D4595 testing method. If appropriate, install fabric silt fence in accordance with BMP C233: Silt Fence to act as high-vis- ibility fence. Silt fence shall be at least 3 feet high and must be highly visible to meet the require- ments of this BMP. Metal fences shall be designed and installed according to the manufacturer's specifications. Metal fences shall be at least 3 feet high and must be highly visible. Fences shall not be wired or stapled to trees. Maintenance Standards If the fence has been damaged or visibility reduced, it shall be repaired or replaced immediately  and visibility restored. BMP C105: Stabilized Construction Access Purpose Stabilized construction accesses are established to reduce the amount of sediment transported  onto paved roads outside the project site by vehicles or equipment. This is done by constructing a  stabilized pad of quarry spalls at entrances and exits for project sites. Conditions of Use Construction accesses shall be stabilized wherever traffic will be entering or leaving a con- struction site if paved roads or other paved areas are within 1,000 feet of the site. For residential subdivision construction sites, provide a stabilized construction access for each  residence, rather than only at the main subdivision entrance. Stabilized surfaces shall be of suf- ficient length/width to provide vehicle access/parking, based on lot size and configuration. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 316Page 18 of 140 On large commercial, highway, and road projects, the designer should include enough extra  materials in the contract to allow for additional stabilized accesses not shown in the initial Con- struction SWPPP. It is difficult to determine exactly where access to these projects will take place;  additional materials will enable the contractor to install them where needed. Design and Installation Specifications  l See Figure II-4.1: Stabilized Construction Access for details. Note: the 100’ minimum length  of the access shall be reduced to the maximum practicable size when the size or con- figuration of the site does not allow the full length (100’).  l Construct stabilized construction accesses with a 12-inch thick pad of 4-inch to 8-inch  quarry spalls, a 4-inch course of asphalt treated base (ATB), or use existing pavement. Do  not use crushed concrete, cement, or calcium chloride for construction access stabilization  because these products raise pH levels in stormwater and concrete discharge to waters of  the State is prohibited.  l A separation geotextile shall be placed under the spalls to prevent fine sediment from pump- ing up into the rock pad. The geotextile shall meet the standards listed in Table II-4.2: Stab- ilized Construction Access Geotextile Standards. Geotextile Property Required Value Grab Tensile  Strength (ASTM D4751)200  psi min. Grab Tensile  Elongation (ASTM D4632)30%  max. Mullen Burst  Strength (ASTM D3786-80a)400  psi min. AOS (ASTM D4751)No. 20 to No. 45  (U.S. standard sieve size) Table II-4.2: Stabilized Construction Access Geotextile Standards  l Consider early installation of the first lift of asphalt in areas that will be paved; this can be  used as a stabilized access. Also consider the installation of excess concrete as a sta- bilized access. During large concrete pours, excess concrete is often available for this pur- pose.  l Fencing (see BMP C103: High-Visibility Fence) shall be installed as necessary to restrict  traffic to the construction access.  l Whenever possible, the access shall be constructed on a firm, compacted subgrade. This  can substantially increase the effectiveness of the pad and reduce the need for main- tenance.  l Construction accesses should avoid crossing existing sidewalks and back of walk drains if  at all possible. If a construction access must cross a sidewalk or back of walk drain, the full  length of the sidewalk and back of walk drain must be covered and protected from sediment  leaving the site. Alternative Material Specification 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 317Page 19 of 140 WSDOT has raised safety concerns about the quarry spall rock specified above. WSDOT  observes that the 4-inch to 8-inch rock sizes can become trapped between dually truck tires, and  then released off-site at highway speeds. WSDOT has chosen to use a modified specification for  the rock while continuously verifying that the stabilized construction access remains effective. To  remain effective, the BMP must prevent sediment from migrating off site. To date, there has been  no performance testing to verify operation of this new specification. Local jurisdictions may use  the alternative specification, but must perform increased off-site inspection if they use, or allow  others to use, it. Stabilized construction accesses may use material that meets the requirements of WSDOT's  Standard Specifications for Road, Bridge, and Municipal Construction Section 9-03.9(1)  (WSDOT, 2016) for ballast except for the following special requirements. The grading and quality requirements are listed in Table II-4.3: Stabilized Construction Access  Alternative Material Requirements. Sieve Size Percent Passing 2½″99 to 100 2″65 to 100 ¾″40 to 80 No. 4 5 max. No. 100 0 to 2 % Fracture 75 min. Notes:   1. All percentages are by weight.  2. The sand equivalent value and dust ratio require- ments do not apply.  3. The fracture requirement shall be at least one  fractured face and will apply the combined  aggregate retained on the No. 4 sieve in accord- ance with FOP for AASHTO T 335. Table II-4.3: Stabilized Construction Access Alternative Material Requirements Maintenance Standards Quarry spalls shall be added if the pad is no longer in accordance with the specifications.  l If the access is not preventing sediment from being tracked onto pavement, then alternative  measures to keep the streets free of sediment shall be used. This may include replace- ment/cleaning of the existing quarry spalls, street sweeping, an increase in the dimensions  2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 318Page 20 of 140 of the access, or the installation of BMP C106: Wheel Wash.  l Any sediment that is tracked onto pavement shall be removed by shoveling or street sweep- ing. The sediment collected by sweeping shall be removed or stabilized on site. The pave- ment shall not be cleaned by washing down the street, except when sweeping is ineffective  and there is a threat to public safety. If it is necessary to wash the streets, the construction  of a small sump to contain the wash water shall be considered. The sediment would then be  washed into the sump where it can be controlled.  l Perform street sweeping by hand or with a high efficiency sweeper. Do not use a non-high  efficiency mechanical sweeper because this creates dust and throws soils into storm sys- tems or conveyance ditches.  l Any quarry spalls that are loosened from the pad, which end up on the roadway shall be  removed immediately.  l If vehicles are entering or exiting the site at points other than the construction access(es),  BMP C103: High-Visibility Fence shall be installed to control traffic.  l Upon project completion and site stabilization, all construction accesses intended as per- manent access for maintenance shall be permanently stabilized. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 319Page 21 of 140 Figure II-4.1: Stabilized Construction Access 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 320Page 22 of 140 Maintenance Standards Inspect stabilized areas regularly, especially after large storm events. Crushed rock, gravel base, etc., shall be added as required to maintain a stable driving surface  and to stabilize any areas that have eroded. Following construction, these areas shall be restored to pre-construction condition or better to pre- vent future erosion. Perform street cleaning at the end of each day or more often if necessary. BMP C120: Temporary and Permanent Seeding Purpose Seeding reduces erosion by stabilizing exposed soils. A well-established vegetative cover is one  of the most effective methods of reducing erosion. Conditions of Use  l Use seeding throughout the project on disturbed areas that have reached final grade or that  will remain unworked for more than 30 days. See II-2.5 Element 5: Stabilize Soils for spe- cific timelines for stabilizing exposed soils.  l See Table II-4.4: Seeding Windows in Western Washington (continued) for appropriate  seeding windows.  l Review all disturbed areas in late August to early September and complete all seeding by  the end of September. Otherwise, vegetation will not establish itself enough to provide  more than average protection.  l Mulch is required at all times for seeding because it protects seeds from heat, moisture  loss, and transport due to runoff. Mulch can be applied on top of the seed or simultaneously  by hydroseeding. See BMP C121: Mulching for specifications.  l Seed and mulch all disturbed areas not otherwise vegetated at final site stabilization. Final  stabilization means the completion of all soil disturbing activities at the site and the estab- lishment of a permanent vegetative cover, or equivalent permanent stabilization measures  (such as pavement, riprap, gabions, or geotextiles) which will prevent erosion. See BMP  T5.13: Post-Construction Soil Quality and Depth. Month Seeding Recommendations January Seeding requires a cover of mulch or an erosion control blanket until 75% grass  cover is establishedFebruary March Table II-4.4: Seeding Windows in Western Washington 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 325Page 23 of 140 Month Seeding Recommendations April Optimum seeding windowMay June July Seeding requires irrigation until 75% grass cover is established August September Optimum seeding window October Seeding requires a cover of mulch or an erosion control blanket until 75 percent  grass cover is establishedNovember December Table II-4.4: Seeding Windows in Western Washington (continued) Design and Installation Specifications General  l Install channels intended for vegetation before starting major earthwork and hydroseed with  a Bonded Fiber Matrix (BFM). For vegetated channels that will have high flows, install  erosion control blankets over the top of hydroseed. Before allowing water to flow in veget- ated channels, establish a 75% vegetation cover. If vegetated channels cannot be estab- lished by seed before water flow, install sod or prevegetated mats in the channel bottom  over top of hydromulch and erosion control blankets.  l Confirm the installation of all required stormwater control measures to prevent seed from  washing away.  l Hydroseed applications shall include a minimum of 1,500 pounds per acre (lb/acre) of  mulch with 3% tackifier. See BMP C121: Mulching for specifications.  l Areas that will have seeding only, and not landscaping, may need compost or meal-based  mulch included in the hydroseed in order to establish vegetation. Re-install native topsoil on  the disturbed soil surface before application. See BMP T5.13: Post-Construction Soil Qual- ity and Depth.  l When installing seed via hydroseeding operations, only about 1/3 of the seed actually ends  up in contact with the soil surface. This reduces the ability to establish a good stand of grass  quickly. To overcome this, consider increasing seed quantities by up to 50 percent.  l Vegetation establishment can be enhanced by one of the following two approaches:  o Approach 1: Enhance vegetation establishment by dividing the hydromulch operation  into two phases: 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 326Page 24 of 140  n Phase 1 – Install all seed and fertilizer with 25% to 30% mulch and tackifier  onto the soil in the first lift.  n Phase 2 – Install the remaining mulch and tackifier over the first lift.  o Approach 2: Vegetation can also be enhanced by:  n Installing the mulch, seed, fertilizer, and tackifier in one lift;   n Spreading or blowing straw over the top of the hydromulch at a rate of about  800 to 1,000 lb/acre; or  n Holding straw in place with a standard tackifier. Both of these approaches (Approach 1 and Approach 2) will increase cost moderately but  will greatly improve and enhance vegetative establishment. The increased cost may be off- set by the reduced need for:  o Irrigation,  o Reapplication of mulch, and   o Repair of failed slope surfaces. Either of these approaches can use standard hydromulch (1,500 lb/acre minimum) and  BFM/mechanically bonded fiber matrix (MBFM) (3,000 lb/acre minimum).  l Seed may be installed by hand if it is:  o Temporary and covered by straw, mulch, or topsoil; or  o Permanent in small areas (usually less than 1 acre) and covered with mulch, topsoil,  or erosion blankets.  l Consult the local suppliers and/or the local conservation district for their recommendations  for appropriate seed mixes and application rates. The appropriate mix depends on a variety  of factors, including location, exposure, soil type, slope, and expected foot traffic.   l In addition to meeting erosion control functions and not hindering maintenance operations,  selection of long-lived, successional growth native vegetation that can compete against or  exclude weeds and grow with minimal maintenance after plant establishment is preferred.  Provide diversity to the greatest extent possible and plan for a succession of flowering  times to improve pollinator habitat.  l The seed mixes listed in Table II-4.5: Temporary and Permanent Seed Mixes for Western  Washington (continued) include recommended mixes for both temporary and permanent  seeding. Alternative seed mixes approved by the local jurisdiction may also be used.  l Apply the mixes in Table II-4.5: Temporary and Permanent Seed Mixes for Western Wash- ington (continued), with the exception of the wet area seed mix, at a rate of 120 pounds per  acre. This rate can be reduced if soil amendments or slow-release fertilizers are used.  Apply the wet area seed mix at a rate of 60 pounds per acre. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 327Page 25 of 140 Common Name Latin Name % Weight % Purity % Germination Temporary Erosion Control Seed Mix A standard mix for areas requiring a temporary vegetative cover. Chewings or  annual  blue grass Festuca rubra var. commutata or  Poa anna 40 98 90 Perennial rye  Lolium perenne 50 98 90 Redtop or colonial  bentgrass  Agrostis alba or  Agrostis tenuis 5 92 85 White dutch clover Trifolium repens 5 98 90 Landscaping Seed Mix A recommended mix for landscaping seed. Perennial rye blend Lolium perenne 70 98 90 Chewings and red  fescue blend Festuca rubra var. commutata or Fes- tuca rubra 30 98 90 Low-Growing Turf Seed Mix A turf seed mix for dry situations where there is no need for watering. This mix requires very little main- tenance. Dwarf tall fescue  (several  varieties) Festuca arundin- acea var. 45 98 90 Dwarf perennial rye  (Barclay) Lolium perenne var. barclay 30 98 90 Red fescue Festuca rubra 20 98 90 Colonial bentgrass Agrostis tenuis 5 98 90 Bioswale Seed Mix A seed mix for bioswales and other intermittently wet areas. Tall or meadow fes- cue Festuca arundin- acea or   Festuca elatior 75-80 98 90 Seaside/Creeping  bentgrass Agrostis palustris 10-15 92 85 Redtop bentgrass Agrostis alba or  Agrostis gigantea 5-10 90 80 Wet Area Seed Mix Table II-4.5: Temporary and Permanent Seed Mixes for Western Washington 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 328Page 26 of 140 Common Name Latin Name % Weight % Purity % Germination A low-growing, relatively non-invasive seed mix appropriate for very wet areas that are not regulated wet- lands. Consult Hydraulic Permit Authority (HPA) for seed mixes if applicable. Tall or meadow fes- cue Festuca arundin- acea or Festuca elatior 60-70 98 90 Seaside/Creeping  bentgrass Agrostis palustris 10-15 98 85 Meadow foxtail Alepocurus pratensis 10-15 90 80 Alsike clover Trifolium hybridum 1-6 98 90 Redtop bentgrass Agrostis alba 1-6 92 85 Meadow Seed Mix A recommended meadow seed mix for infrequently maintained areas or non-maintained areas where  colonization by native plants is desirable. Likely applications include rural road and utility right-of-way.  Seeding should take place in September or very early October in order to obtain adequate establishment  prior to the winter months. Consider the appropriateness of clover, a fairly invasive species, in the mix.  Amending the soil can reduce the need for clover. Redtop or Oregon  bentgrass Agrostis alba or  Agrostis ore- gonensis 20 92 85 Red fescue Festuca rubra 70 98 90 White dutch clover Trifolium repens 10 98 90 Table II-4.5: Temporary and Permanent Seed Mixes for Western Washington (continued) Roughening and Rototilling  l The seedbed should be firm and rough. Roughen all soil no matter what the slope. Track  walk slopes before seeding if engineering purposes require compaction. Backblading or  smoothing of slopes greater than 4H:1V is not allowed if they are to be seeded.  l Restoration-based landscape practices require deeper incorporation than that provided by  a simple, single-pass rototilling treatment. Wherever practical, initially rip the subgrade to  improve long-term permeability, infiltration, and water inflow qualities. At a minimum, per- manent areas shall receive soil amendments to achieve organic matter and permeability  performance defined in engineered soil/landscape systems. For systems that are deeper  than 8 inches, complete the rototilling process in multiple lifts, or prepare the soil amend- ments per the specifications and place to achieve the specified depth. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 329Page 27 of 140 Fertilizers  l Conducting soil tests to determine the exact type and quantity of fertilizer needed is recom- mended. This will prevent the overapplication of fertilizer.  l Organic matter is the most appropriate form of fertilizer because it provides nutrients (includ- ing nitrogen, phosphorus, and potassium) in the least water-soluble form.  l In general, use 10-4-6 N-P-K (nitrogen-phosphorus-potassium) fertilizer at a rate of 90  pounds per acre.   l Always use slow-release fertilizers because they are more efficient and have fewer envir- onmental impacts. Do not add fertilizer to the hydromulch machine, or agitate, more than 20  minutes before use. Too much agitation destroys the slow-release coating.  l There are numerous products available to take the place of chemical fertilizers, including  several with seaweed extracts that are beneficial to soil microbes and organisms. If 100%  cottonseed meal is used as the mulch in hydroseed, chemical fertilizer may not be neces- sary. Cottonseed meal provides a good source of long-term, slow-release, available nitro- gen.  Bonded Fiber Matrix and Mechanically Bonded Fiber Matrix  l On steep slopes, use Bonded Fiber Matrix (BFM) or Mechanically Bonded Fiber Matrix  (MBFM) products. Apply BFM/MBFM products at a minimum rate of 3,000 pounds per acre  with approximately 10% tackifier. Achieve a minimum of 95% soil coverage during applic- ation. Numerous products are available commercially. Most products require 24-36 hours to  cure before rainfall, and cannot be installed on wet or saturated soils. Generally, products  come in 40-50 pound bags and include all necessary ingredients except for seed and fer- tilizer.  l Install products per manufacturer's instructions.  l BFMs and MBFMs provide good alternatives to blankets in most areas requiring vegetation  establishment. Advantages over blankets include the following:  o BFM and MBFMs do not require surface preparation.  o Helicopters can assist in installing BFM and MBFMs in remote areas.  o On slopes steeper than 2.5H:1V, blanket installers may require ropes and harnesses  for safety.  o Installing BFM and MBFMs can save at least $1,000 per acre compared to blankets. Maintenance Standards  l Reseed any seeded areas that fail to establish at least 75% cover (100% cover for areas  that receive sheet or concentrated flows) of all seeded areas after 3 months of active  growth following germination during the growing season. If reseeding is ineffective, use an  alternate method, such as sodding, mulching, or nets/blankets. If winter weather prevents  2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 330Page 28 of 140 adequate grass growth, this time limit may be relaxed at the discretion of the local authority  when sensitive areas would otherwise be protected.  l Reseed and protect by mulch any areas that experience erosion after achieving adequate  cover. If the erosion problem is drainage related, the problem shall be fixed and the eroded  area reseeded and protected by mulch.  l Supply seeded areas with adequate moisture, but do not water to the extent that it causes  runoff. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did  not pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jur- isdictions may choose not to accept these products, or may require additional testing prior to con- sideration for local use. Products that Ecology has approved as functionally equivalent are  available for review on Ecology’s website at:  https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per- mittee-guidance-resources/Emerging-stormwater-treatment-technologies BMP C121: Mulching Purpose Mulching soils provides immediate temporary protection from erosion. Mulch also enhances plant  establishment by conserving moisture, holding fertilizer, seed, and topsoil in place, and mod- erating soil temperatures. There are a variety of mulches that can be used. This section discusses  only the most common types of mulch. Conditions of Use As a temporary cover measure, mulch should be used:  l For less than 30 days on disturbed areas that require cover.  l At all times for seeded areas, especially during the wet season and during the hot summer  months.  l During the wet season on slopes steeper than 3H:1V with more than 10 feet of vertical  relief. Mulch may be applied at any time of the year and must be refreshed periodically. For seeded areas, mulch may be made up of 100 percent:   l Cottonseed meal;   l Fibers made of wood, recycled cellulose, hemp, or kenaf;  2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 331Page 29 of 140  l Compost;   l Or blends of these. Tackifier shall be plant-based, such as guar or alpha plantago, or chemical-based such as poly- acrylamide or polymers.  Generally, mulches come in 40-50 pound bags. Seed and fertilizer are added at time of applic- ation. Recycled cellulose may contain polychlorinated biphenyl (PCBs). Ecology recommends that  products should be evaluated for PCBs prior to use. Refer to BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection for conditions of use. PAM  shall not be directly applied to water or allowed to enter a water body. Any mulch or tackifier product used shall be installed per the manufacturer’s instructions. Design and Installation Specifications For mulch materials, application rates, and specifications, see Table II-4.7: Mulch Standards and  Guidelines (continued). Consult with the local supplier or the local conservation district for their  recommendations. Increase the application rate until the ground is 95% covered (i.e. not visible  under the mulch layer). Note: Thickness may be increased for disturbed areas in or near sensitive  areas or other areas highly susceptible to erosion. Where the option of “Compost” is selected, it should be a coarse compost that meets the size grad- ations listed in Table II-4.6: Size Gradations of Compost as Mulch Material when tested in accord- ance with Test Method 02.02-B found in Test Methods for the Examination of Composting and Compost (Thompson, 2001). Mulch used within the ordinary high-water mark of surface waters should be selected to minimize  potential flotation of organic matter. Composted organic materials have higher specific gravities  (densities) than straw, wood, or chipped material. Consult the Hydraulic Permit Authority (HPA)  for mulch mixes if applicable. Sieve Size Percent Passing 3"100% 1"90% - 100% 3/4"70% - 100% 1/4"40% - 100% Table II-4.6: Size Gradations of Compost as Mulch Material Mulch Mater- ial Guideline Description Straw Quality Stand-Air-dried; free from undesirable seed and coarse material. Table II-4.7: Mulch Standards and Guidelines 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 332Page 30 of 140 Mulch Mater- ial Guideline Description ards Application Rates 2" to 3" thick; 5 bales per 1,000 sf or 2 to 3 tons per acre Remarks Cost-effective protection when applied with adequate thickness.  Hand-application generally requires greater thickness than blown  straw. The thickness of straw may be reduced by half when used in  conjunction with seeding. In windy areas, straw must be held in  place by crimping, using a tackifier, or covering with netting. Blown  straw always has to be held in place with a tackifier because even  light winds will blow it away. Straw, however, has several defi- ciencies that should be considered when selecting mulch materials.  It often introduces and/or encourages the propagation of weed spe- cies, and it has no significant long-term benefits. Straw should only  be used if mulches with long-term benefits are unavailable locally. It  should also not be used within the ordinary high-water elevation of  surface waters (due to flotation). Hydromulch Quality Stand- ards No growth inhibiting factors. Application Rates Approx. 35-45 lbs per 1,000 sf or 1,500 - 2,000 lbs per acre Remarks Shall be applied with hydromulcher. Shall not be used without seed  and tackifier unless the application rate is at least doubled. Fibers  longer than about 3/4 - 1 inch clog hydromulch equipment. Fibers  should be kept to less than 3/4 inch. Compost Quality Stand- ards No visible water or dust during handling. Must be produced per WAC  173-350, Solid Waste Handling Standards, but may have up to 35%  biosolids. Application Rates 2" thick minimum; approximately 100 tons per acre (approximately  750 lbs per cubic yard) Remarks More effective control can be obtained by increasing thickness to 3".  Compost makes an excellent mulch for protecting final grades until  landscaping because it can be directly seeded or tilled into soil as an  amendment. Compost used for mulch has a coarser size gradation  than compost used for BMP C125: Topsoiling / Composting or BMP  T5.13: Post-Construction Soil Quality and Depth. It is more stable  and practical to use in wet areas and during rainy weather con- ditions. Do not use compost near wetlands if biosolids are included.  Do not use compost near phosphorous impaired water bodies. Chipped Site Vegetation Quality Stand- ards Gradations from fines to 6 inches in length for texture, variation, and  interlocking properties. Include a mix of various sizes so that the  Table II-4.7: Mulch Standards and Guidelines (continued) 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 333Page 31 of 140 Mulch Mater- ial Guideline Description average size is between 2 and 4 inches. Application Rates 2" thick minimum. Remarks This is a cost-effective way to dispose of debris from clearing and  grubbing, and it eliminates the problems associated with burning.  Generally, it should not be used on slopes above approximately 10%  because of its tendency to be transported by runoff. It is not recom- mended within 200 feet of surface waters. If permanent seeding or  planting is expected shortly after mulch, the decomposition of the  chipped vegetation may tie up nutrients important to grass estab- lishment.  Note: Thick application of this material over existing grass, herb- aceous species, and some groundcovers could smother and kill  vegetation. Wood-Based Mulch Quality Stand- ards No visible water or dust during handling. Must be purchased from a  supplier with a Solid Waste Handling Permit or one exempt from  solid waste regulations. Application Rates 2" thick minimum; approximately 100 tons per acre (approximately  750 lbs. per cubic yard). Remarks This material is often called "wood straw" or "hog fuel". The use of  mulch ultimately improves the organic matter in the soil. Special cau- tion is advised regarding the source and composition of wood-based  mulches. Its preparation typically does not provide any weed seed  control, so evidence of residual vegetation in its composition or  known inclusion of weed plants or seeds should be monitored and  prevented (or minimized). Wood Strand Mulch Quality Stand- ards A blend of loose, long, thin wood pieces derived from native conifer  or deciduous trees with high length-to-width ratio. Application Rates 2" thick minimum. Remarks Cost-effective protection when applied with adequate thickness. A  minimum of 95% of the wood strand shall have lengths between 2  and 10 inches, with a width and thickness between 1/16 and 0.5  inches. The mulch shall not contain resin, tannin, or other com- pounds in quantities that would be detrimental to plant life. Sawdust  or wood shavings shall not be used as mulch. See specification 9- 14.4(4) from the Standard Specifications for Road, Bridge, and Muni- cipal Construction (WSDOT, 2016) Table II-4.7: Mulch Standards and Guidelines (continued) Maintenance Standards The thickness of the mulch cover must be maintained. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 334Page 32 of 140 BMP C123: Plastic Covering Purpose Plastic covering provides immediate, short-term erosion protection to slopes and disturbed areas. Conditions of Use Plastic covering may be used on disturbed areas that require cover measures for less than 30  days, except as stated below.  l Plastic is particularly useful for protecting cut and fill slopes and stockpiles. However, the rel- atively rapid breakdown of most polyethylene sheeting makes it unsuitable for applications  greater than six months.  l Due to rapid runoff caused by plastic covering, do not use this method upslope of areas that  might be adversely impacted by concentrated runoff. Such areas include steep and/or  unstable slopes.  l Plastic sheeting may result in increased runoff volumes and velocities, requiring additional  on-site measures to counteract the increases. Creating a trough with wattles or other mater- ial can convey clean water away from these areas.  l To prevent undercutting, trench and backfill rolled plastic covering products.  l Although the plastic material is inexpensive to purchase, the cost of installation, main- tenance, removal, and disposal add to the total costs of this BMP.  l Whenever plastic is used to protect slopes, install water collection measures at the base of  the slope. These measures include plastic-covered berms, channels, and pipes used to con- vey clean rainwater away from bare soil and disturbed areas. Do not mix clean runoff from a  plastic covered slope with dirty runoff from a project.  l Other uses for plastic include:  o Temporary ditch liner.  o Pond liner in temporary sediment pond.  o Liner for bermed temporary fuel storage area if plastic is not reactive to the type of  fuel being stored.  o Emergency slope protection during heavy rains.  o Temporary drainpipe (“elephant trunk”) used to direct water. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 340Page 33 of 140 Design and Installation Specifications  l Plastic slope cover must be installed as follows:  1. Run plastic up and down the slope, not across the slope.  2. Plastic may be installed perpendicular to a slope if the slope length is less than 10  feet.  3. Provide a minimum of 8-inch overlap at the seams.  4. On long or wide slopes, or slopes subject to wind, tape all seams.  5. Place plastic into a small (12-inch wide by 6-inch deep) slot trench at the top of the  slope and backfill with soil to keep water from flowing underneath.  6. Place sand filled burlap or geotextile bags every 3 to 6 feet along seams and tie them  together with twine to hold them in place.  7. Inspect plastic for rips, tears, and open seams regularly and repair immediately. This  prevents high velocity runoff from contacting bare soil, which causes extreme  erosion.  8. Sandbags may be lowered into place tied to ropes. However, all sandbags must be  staked in place.  l Plastic sheeting shall have a minimum thickness of 6 mil.  l If erosion at the toe of a slope is likely, a gravel berm, riprap, or other suitable protection  shall be installed at the toe of the slope in order to reduce the velocity of runoff. Maintenance Standards  l Torn sheets must be replaced and open seams repaired.  l Completely remove and replace the plastic if it begins to deteriorate due to ultraviolet radi- ation.  l Completely remove plastic when no longer needed.  l Dispose of old tires used to weight down plastic sheeting appropriately. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did  not pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jur- isdictions may choose not to accept these products, or may require additional testing prior to con- sideration for local use. Products that Ecology has approved as functionally equivalent are  available for review on Ecology’s website at:  https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per- mittee-guidance-resources/Emerging-stormwater-treatment-technologies 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 341Page 34 of 140 BMP C124: Sodding Purpose The purpose of sodding is to establish turf for immediate erosion protection and to stabilize drain- age paths where concentrated overland flow will occur. Conditions of Use Sodding may be used in the following areas:  l Disturbed areas that require short-term or long-term cover.  l Disturbed areas that require immediate vegetative cover.  l All waterways that require vegetative lining. Waterways may also be seeded rather than  sodded, and protected with a net or blanket. Design and Installation Specifications Sod shall be free of weeds, have a uniform thickness (approximately 1-inch thick), and have a  dense root mat for mechanical strength. The following steps are recommended for sod installation:  1. Shape and smooth the surface to final grade in accordance with the approved grading plan.  Consider any areas (such as swales) that  need to be overexcavated below design elevation  to allow room for placing soil amendment and sod.  2. Amend 4 inches (minimum) of compost into the top 8 inches of the soil if the organic content  of the soil is less than ten percent or the permeability is less than 0.6 inches per hour. See  Ecology's Compost web page for further information: https://ecology.wa.gov/Waste-Toxics/Reducing-recycling-waste/Organic-mater- ials/Managing-organics-compost  3. Fertilize according to the sod supplier's recommendations.  4. Work lime and fertilizer 1 to 2 inches into the soil, and smooth the surface.  5. Lay strips of sod beginning at the lowest area to be sodded and perpendicular to the dir- ection of water flow. Wedge strips securely into place. Square the ends of each strip to  provide for a close, tight fit. Stagger joints at least 12 inches. Staple on slopes steeper than  3H:1V. Staple the upstream edge of each sod strip.  6. Roll the sodded area and irrigate.  7. When sodding is carried out in alternating strips or other patterns, seed the areas between  the sod immediately after sodding. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 342Page 35 of 140 Maintenance Standards If the grass is unhealthy, the cause shall be determined and appropriate action taken to rees- tablish a healthy ground cover. If it is impossible to establish a healthy ground cover due to fre- quent saturation, instability, or some other cause, the sod shall be removed, the area seeded with  an appropriate mix, and protected with a net or blanket (BMP C122: Nets and Blankets). BMP C125: Topsoiling / Composting Purpose Topsoiling and composting provide a suitable growth medium for final site stabilization with veget- ation. While not a permanent cover practice in itself, topsoiling and composting are an integral  component of providing permanent cover in those areas where there is an unsuitable soil surface  for plant growth. Use this BMP in conjunction with other BMPs such as BMP C120: Temporary  and Permanent Seeding, BMP C121: Mulching, or BMP C124: Sodding.  Implementation of this BMP may meet the post-construction requirements of BMP T5.13: Post- Construction Soil Quality and Depth. Native soils and disturbed soils that have been organically amended not only retain much more  stormwater, but also serve as effective biofilters for urban pollutants and, by supporting more vig- orous plant growth, reduce the water, fertilizer, and/or pesticides needed to support installed land- scapes. Topsoil does not include any subsoils but only the material from the top several inches  including organic debris. Conditions of Use  l Permanent landscaped areas shall contain healthy topsoil that reduces the need for fer- tilizers, improves overall topsoil quality, provides for better vegetative health and vitality,  improves hydrologic characteristics, and reduces the need for irrigation.  l Leave native soils and the duff layer undisturbed to the maximum extent practicable. Strip- ping of existing, properly functioning soil system and vegetation for the purpose of top- soiling during construction is not acceptable. Preserve existing soil systems in undisturbed  and uncompacted conditions if functioning properly.  l Areas that already have good topsoil, such as undisturbed areas, do not require soil amend- ments.  l Restore, to the maximum extent practical, native soils disturbed during clearing and grading  to a condition equal to or better than the original site condition’s moisture-holding capacity.  Use on-site native topsoil, incorporate amendments into on-site soil, or import blended top- soil to meet this requirement.  l Topsoiling is a required procedure when establishing vegetation on shallow soils, and soils  of critically low pH (high acid) levels. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 343Page 36 of 140  l Beware of where the topsoil comes from, and what vegetation was on site before dis- turbance. Invasive plant seeds may be included and could cause problems for establishing  native plants, landscaped areas, or grasses.  l Topsoil from the site will contain mycorrhizal bacteria that are necessary for healthy root  growth and nutrient transfer. These native mycorrhizae are acclimated to the site and will  provide optimum conditions for establishing grasses. Use commercially available mycor- rhizae products when using off-site topsoil. Design and Installation Specifications Meet the following requirements for disturbed areas where topsoil will be applied (e.g. for dis- turbed areas that will be developed as lawn or other landscape):  l Maximize the depth of the topsoil wherever possible to provide the maximum possible infilt- ration capacity and beneficial growth medium. Topsoil shall have:  o A minimum depth of 8 inches. Scarify subsoils below the topsoil layer at least 4  inches with some incorporation of the upper material to avoid stratified layers, where  feasible. Ripping or re-structuring the subgrade may also provide additional benefits  regarding the overall infiltration and interflow dynamics of the soil system. The  decision to either layer topsoil over a subgrade or incorporate topsoil into the under- lying layer may vary depending on the planting specified.  o A minimum organic content of 10% dry weight in planting beds, and 5% organic mat- ter content in turf areas. Incorporate organic amendments to a minimum 8 inch depth  except where tree roots or other natural features limit the depth of incorporation.  o A pH between 6.0 and 8.0 or matching the pH of the undisturbed soil.  o If blended topsoil is imported, then fines should be limited to 25% passing through a  200 sieve.  l Mulch planting beds with 2 inches of organic material  l Accomplish the required organic content, depth, and pH by returning native topsoil to the  site, importing topsoil of sufficient organic content, and/or incorporating organic amend- ments. When using the option of incorporating amendments to meet the organic content  requirement, use compost that meets the compost specification for Bioretention (See BMP  T7.30: Bioretention), with the exception that the compost may have up to 35% biosolids or  manure.  l The final composition and construction of the soil system will result in a natural selection or  favoring of certain plant species over time. For example, incorporation of topsoil may favor  grasses, while layering with mildly acidic, high-carbon amendments may favor more woody  vegetation.  l Allow sufficient time in scheduling for topsoil spreading prior to seeding, sodding, or plant- ing. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 344Page 37 of 140  l Take care when applying topsoil to subsoils with contrasting textures. Sandy topsoil over  clayey subsoil is a particularly poor combination, as water creeps along the junction  between the soil layers and causes the topsoil to slough. If topsoil and subsoil are not prop- erly bonded, water will not infiltrate the soil profile evenly and it will be difficult to establish  vegetation. The best method to promote bonding is to actually work the topsoil into the layer  below for a depth of at least 6 inches.  l Field exploration of the site shall be made to determine if there is surface soil of sufficient  quantity and quality to justify stripping. Topsoil shall be friable and loamy (loam, sandy  loam, silt loam, sandy clay loam, and/or clay loam). Avoid areas of natural groundwater  recharge.  l Stripping shall be confined to the immediate construction area. A 4 to 6 inch stripping depth  is common, but depth may vary depending on the particular soil. All surface runoff control  structures shall be in place prior to stripping.  l Do not place topsoil while in a frozen or muddy condition, when the subgrade is excessively  wet, or when conditions exist that may otherwise be detrimental to proper grading or pro- posed sodding or seeding.  l In any areas requiring grading, remove and stockpile the duff layer and topsoil on site in a  designated, controlled area, not adjacent to public resources and critical areas. Reapply  stockpiled topsoil to other portions of the site where feasible.  l Locate the topsoil stockpile so that it meets specifications and does not interfere with work  on the site. It may be possible to locate more than one pile in proximity to areas where top- soil will be used.  l Stockpiling of topsoil shall occur in the following manner:  o Side slopes of the stockpile shall not exceed 2H:1V.  o Between October 1 and April 30:  n An interceptor dike with gravel outlet and silt fence shall surround all topsoil  stockpiles.  n Within 2 days complete erosion control seeding, or covering stockpiles with  clear plastic, or other mulching materials.  o Between May 1 and September 30:  n An interceptor dike with gravel outlet and silt fence shall surround all topsoil  stockpiles if the stockpile will remain in place for a longer period of time than  active construction grading.  n Within 7 days complete erosion control seeding, or covering stockpiles with  clear plastic, or other mulching materials.  l When native topsoil is to be stockpiled and reused, the following should apply to ensure that  the mycorrhizal bacteria, earthworms, and other beneficial organisms will not be destroyed: 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 345Page 38 of 140  o Reinstall topsoil within 4 to 6 weeks.  o Do not allow the saturation of topsoil with water.  o Do not use plastic covering. Maintenance Standards  l Inspect stockpiles regularly, especially after large storm events. Stabilize any areas that  have eroded.  l Establish soil quality and depth toward the end of construction and once established, pro- tect from compaction, such as from large machinery use, and from erosion.  l Plant and mulch soil after installation.  l Leave plant debris or its equivalent on the soil surface to replenish organic matter.  l Reduce and adjust, where possible, the use of irrigation, fertilizers, herbicides and pesti- cides, rather than continuing to implement formerly established practices. BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection Purpose Polyacrylamide (PAM) is used on construction sites to prevent soil erosion. Applying PAM to bare soil in advance of a rain event significantly reduces erosion and controls  sediment in two ways. First, PAM increases the soil’s available pore volume, thus increasing infilt- ration and reducing the quantity of stormwater runoff. Second, it increases flocculation of sus- pended particles and aids in their deposition, thus reducing stormwater runoff turbidity and  improving water quality. Conditions of Use PAM shall not be directly applied to water or allowed to enter a water body. Stormwater runoff  from areas where PAM has been applied shall pass through BMP C240: Sediment Trap or BMP  C241: Sediment Pond (Temporary) (depending on the size of the drainage area) prior to dis- charging to surface waters. PAM use shall be reviewed and approved by the local jurisdiction. Loss of sediment and PAM may be a basis for penalties per RCW 90.48.080. PAM can be applied to bare soil under the following conditions:  l During rough grading operations.  l In staging areas.  l In balanced cut and fill earthwork. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 346Page 39 of 140 BMP C140: Dust Control Purpose Dust control prevents wind transport of dust from disturbed soil surfaces onto roadways, into drain- age systems, and into surface waters. Conditions of Use Use dust control in areas (including roadways) subject to surface and air movement of dust where  on-site or off-site impacts to roadways, drainage systems, or surface waters are likely. Design and Installation Specifications  l Vegetate or mulch areas that will not receive vehicle traffic. In areas where planting, mulch- ing, or paving is impractical, apply gravel or landscaping rock.  l Limit dust generation by clearing only those areas where immediate activity will take place,  leaving the remaining area(s) in the original condition. Maintain the original ground cover as  long as practical.  l Construct natural or artificial windbreaks or windscreens. These may be designed as  enclosures for small dust sources.  l Sprinkle the site with water until the surface is wet. Repeat as needed. To prevent carryout  of mud onto the street, refer to BMP C105: Stabilized Construction Access and BMP C106:  Wheel Wash.  l Irrigation water can be used for dust control. Irrigation systems should be installed as a first  step on sites where dust control is a concern.  l Spray exposed soil areas with a dust palliative, following the manufacturer’s instructions  and cautions regarding handling and application. Used oil is prohibited from use as a dust  suppressant. Local jurisdictions may approve other dust palliatives such as calcium chlor- ide or PAM.  l PAM (BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection) added to water at a  rate of 0.5 pounds per 1,000 gallons of water per acre and applied from a water truck is  more effective than water alone. This is due to the increased infiltration of water into the soil  and reduced evaporation. In addition, small soil particles are bonded together and are not  as easily transported by wind. Adding PAM may reduce the quantity of water needed for  dust control.  Note that the application rate specified here applies to this BMP, and is not the same applic- ation rate that is specified in BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection,  but the downstream protections still apply. Refer to BMP C126: Polyacrylamide (PAM) for Soil Erosion Protection for conditions of use.  PAM shall not be directly applied to water or allowed to enter a water body. PAM use shall  2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 356Page 40 of 140 be reviewed and approved by the local permitting authority and discharge of PAM may be a  basis for penalties per RCW 90.48.080.  l Contact your local Air Pollution Control Authority for guidance and training on other dust  control measures. Compliance with the local Air Pollution Control Authority constitutes com- pliance with this BMP. See the following website for more information: https://ecology.wa.gov/About-us/Our-role-in-the-community/Partnerships-com- mittees/Clean-air-agencies  l Use vacuum street sweepers.  l Remove mud and other dirt promptly so it does not dry and then turn into dust.  l Techniques that can be used for unpaved roads and lots include:  o Lower speed limits. High vehicle speed increases the amount of dust stirred up from  unpaved roads and lots.  o Upgrade the road surface strength by improving particle size, shape, and mineral  types that make up the surface and base materials.  o Add surface gravel to reduce the source of dust emission. Limit the amount of fine  particles (those smaller than .075 mm) to 10 to 20 percent.  o Use geotextile fabrics to increase the strength of new roads or roads undergoing  reconstruction.  o Encourage the use of alternate, paved routes, if available.  o Apply chemical dust suppressants using the admix method, blending the product with  the top few inches of surface material. Suppressants may also be applied as surface  treatments.  o Limit dust-generating work on windy days.  o Pave unpaved permanent roads and other trafficked areas. Maintenance Standards Respray area as necessary to keep dust to a minimum. BMP C150: Materials on Hand Purpose Keep quantities of erosion prevention and sediment control materials on the project site at all  times to be used for regular maintenance and emergency situations such as unexpected heavy  rains. Having these materials on-site reduces the time needed to replace existing or implement  new BMPs when inspections indicate that existing BMPs are not meeting the Construction  SWPPP requirements. In addition, contractors can save money by buying some materials in bulk  and storing them at their office or yard. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 357Page 41 of 140 BMP C151: Concrete Handling Purpose Concrete work can generate process water and slurry that contain fine particles and high pH, both  of which can violate water quality standards in the receiving water. Concrete spillage or concrete  discharge to waters of the State is prohibited. Use this BMP to minimize and eliminate concrete,  concrete process water, and concrete slurry from entering waters of the State. Conditions of Use Any time concrete is used, utilize these management practices. Concrete construction project  components include, but are not limited to:  l Curbs  l Sidewalks  l Roads  l Bridges  l Foundations  l Floors  l Runways Disposal options for concrete, in order of preference are:  1. Off-site disposal  2. Concrete wash-out areas (see BMP C154: Concrete Washout Area)  3. De minimus washout to formed areas awaiting concrete Design and Installation Specifications  l Wash concrete truck drums at an approved off-site location or in designated concrete  washout areas only. Do not wash out  concrete trucks onto the ground (including formed  areas awaiting concrete), or into storm drains, open ditches, streets, or streams. Refer to  BMP C154: Concrete Washout Area for information on concrete washout areas.  o Return unused concrete remaining in the truck and pump to the originating batch  plant for recycling. Do not dump excess concrete on site, except in designated con- crete washout areas as allowed in BMP C154: Concrete Washout Area.  l Wash small concrete handling equipment (e.g. hand tools, screeds, shovels, rakes, floats,  trowels, and wheelbarrows) into designated concrete washout areas or into formed areas  awaiting concrete pour. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 359Page 42 of 140  l At no time shall concrete be washed off into the footprint of an area where an infiltration fea- ture will be installed.  l Wash equipment difficult to move, such as concrete paving machines, in areas that do not  directly drain to natural or constructed stormwater conveyance or potential infiltration areas.  l Do not allow washwater from areas, such as concrete aggregate driveways, to drain directly  (without detention or treatment) to natural or constructed stormwater conveyances.  l Contain washwater and leftover product in a lined container when no  designated concrete  washout areas (or formed areas, allowed as described above) are available. Dispose of con- tained concrete and concrete washwater (process water) properly.  l Always use forms or solid barriers for concrete pours, such as pilings, within 15-feet of sur- face waters.  l Refer to BMP C252: Treating and Disposing of High pH Water for pH adjustment require- ments.  l Refer to the Construction Stormwater General Permit (CSWGP) for pH monitoring require- ments if the project involves one of the following activities:  o Significant concrete work (as defined in the CSWGP).  o The use of soils amended with (but not limited to) Portland cement-treated base,  cement kiln dust or fly ash.  o Discharging stormwater to segments of water bodies on the 303(d) list (Category 5)  for high pH. Maintenance Standards Check containers for holes in the liner daily during concrete pours and repair the same day. BMP C152: Sawcutting and Surfacing Pollution Prevention Purpose Sawcutting and surfacing operations generate slurry and process water that contain fine particles  and have a high pH (concrete cutting), both of which can violate the water quality standards in the  receiving water. Concrete spillage or concrete discharge to waters of the State is prohibited. Use  this BMP to minimize and eliminate process water and slurry created by sawcutting or surfacing  from entering waters of the State. Conditions of Use Utilize these management practices anytime sawcutting or surfacing operations take place. Saw- cutting and surfacing operations include, but are not limited to: 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 360Page 43 of 140  l Sawing  l Coring  l Grinding  l Roughening  l Hydro-demolition  l Bridge and road surfacing Design and Installation Specifications  l Vacuum slurry and cuttings during cutting and surfacing operations.  l Slurry and cuttings shall not remain on permanent concrete or asphalt pavement overnight.  l Slurry and cuttings shall not drain to any natural or constructed drainage conveyance includ- ing stormwater systems. This may require temporarily blocking catch basins.  l Dispose of collected slurry and cuttings in a manner that does not violate groundwater or  surface water quality standards.  l Do not allow process water generated during hydro-demolition, surface roughening, or sim- ilar operations to drain to any natural or constructed drainage conveyance including storm- water systems. Dispose of process water in a manner that does not violate groundwater or  surface water quality standards.  l Handle and dispose of cleaning waste material and demolition debris in a manner that does  not cause contamination of water. Dispose of sweeping material from a pick-up sweeper at  an appropriate disposal site. Maintenance Standards Continually monitor operations to determine whether slurry, cuttings, or process water could enter  waters of the state. If inspections show that a violation of water quality standards could occur, stop  operations and immediately implement preventive measures such as berms, barriers, secondary  containment, and/or vacuum trucks. BMP C153: Material Delivery, Storage, and Containment Purpose Prevent, reduce, or eliminate the discharge of pollutants to the stormwater system or water- courses from material delivery and storage. Minimize the storage of hazardous materials on-site,  store materials in a designated area, and install secondary containment. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 361Page 44 of 140 Conditions of Use Use at construction sites with delivery and storage of the following materials:  l Petroleum products such as fuel, oil and grease  l Soil stabilizers and binders (e.g., polyacrylamide)  l Fertilizers, pesticides, and herbicides  l Detergents  l Asphalt and concrete compounds  l Hazardous chemicals such as acids, lime, adhesives, paints, solvents, and curing com- pounds  l Any other material that may be detrimental if released to the environment Design and Installation Specifications  l The temporary storage area should be located away from vehicular traffic, near the con- struction entrance(s), and away from waterways or storm drains.  l Safety Data Sheets (SDS) should be supplied for all materials stored. Chemicals should be  kept in their original labeled containers.  l Hazardous material storage on-site should be minimized.  l Hazardous materials should be handled as infrequently as possible.  l During the wet weather season (October 1 – April 30), consider storing materials in a  covered area.  l Materials should be stored in secondary containments, such as an earthen dike, horse  trough, or even a children’s wading pool for non-reactive materials such as detergents, oil,  grease, and paints. Small amounts of material may be secondarily contained in “bus boy”  trays or concrete mixing trays.  l Do not store chemicals, drums, or bagged materials directly on the ground. Place these  items on a pallet and, when possible, within secondary containment.  l If drums must be kept uncovered, store them at a slight angle to reduce ponding of rain- water on the lids to reduce corrosion. Domed plastic covers are inexpensive and snap to  the top of drums, preventing water from collecting.  l Liquids, petroleum products, and substances listed in 40 CFR Parts 110, 117, or 302 shall  be stored in approved containers and drums and shall not be overfilled. Containers and  drums shall be stored in temporary secondary containment facilities.  l Temporary secondary containment facilities shall provide for a spill containment volume  able to contain 10% of the total enclosed container volume of all containers, or 110% of the  capacity of the largest container within its boundary, whichever is greater. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 362Page 45 of 140  l Secondary containment facilities shall be impervious to the materials stored therein for a  minimum contact time of 72 hours.  l Sufficient separation should be provided between stored containers to allow for spill  cleanup and emergency response access.  l During the wet weather season (Oct 1 – April 30), each secondary containment facility shall  be covered during non-working days.  l Secondary containment facilities shall be covered at all times, except when in active use.  l Keep material storage areas clean, organized, and equipped with an ample supply of appro- priate spill clean-up material (spill kit).  l The spill kit should include, at a minimum:  o 1 - Water resistant nylon bag  o 3 - Oil absorbent socks 3”x 4’  o 2 - Oil absorbent socks 3”x 10’  o 12 - Oil absorbent pads 17”x19”  o 1 - Pair splash resistant goggles  o 3 - Pairs nitrile gloves  o 10 - Disposable bags with ties  o Instructions Maintenance Standards  l Secondary containment facilities shall be maintained free of accumulated rainwater and  spills. In the event of spills or leaks, accumulated rainwater and spills shall be collected and  placed into drums. These liquids shall be handled as hazardous waste unless testing  determines them to be non-hazardous.  l Re-stock spill kit materials as needed. BMP C154: Concrete Washout Area Purpose Prevent or reduce the discharge of pollutants from concrete waste to stormwater by conducting  washout off-site, or performing on-site washout in a designated area. Conditions of Use Concrete washout areas are implemented on construction projects where: 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 363Page 46 of 140 BMP C160: Certified Erosion and Sediment Control Lead Purpose The project proponent designates at least one person as the responsible representative in charge  of erosion and sediment control (ESC) and water quality protection. The designated person shall  be responsible for ensuring compliance with all local, state, and federal erosion and sediment con- trol and water quality requirements. Construction sites one acre or larger that discharge to waters  of the State must designate a Certified Erosion and Sediment Control Lead (CESCL) as the  responsible representative. Conditions of Use A CESCL shall be made available on projects one acre or larger that discharge stormwater to sur- face waters of the state. Sites less than one acre may have a person without CESCL certification  conduct inspections. The CESCL shall:  l Have a current certificate proving attendance in an ESC training course that meets the min- imum ESC training and certification requirements established by Ecology. Ecology has provided the minimum requirements for CESCL course training, as well as a  list of ESC training and certification providers at:  https://ecology.wa.gov/Regulations-Permits/Permits-certifications/Certified-erosion-sed- iment-control  OR  l Be a Certified Professional in Erosion and Sediment Control (CPESC). For additional  information go to:  http://www.envirocertintl.org/cpesc/ Specifications  l CESCL certification shall remain valid for three years.  l The CESCL shall have authority to act on behalf of the contractor or project proponent and  shall be available, or on-call, 24 hours per day throughout the period of construction.  l The Construction SWPPP shall include the name, telephone number, fax number, and  address of the designated CESCL. See II-3 Construction Stormwater Pollution Prevention  Plans (Construction SWPPPs).  l A CESCL may provide inspection and compliance services for multiple construction pro- jects in the same geographic region, but must be on site whenever earthwork activities are  occurring that could generate release of turbid water. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 371Page 47 of 140  l Duties and responsibilities of the CESCL shall include, but are not limited to, the following:  o Maintaining a permit file on site at all times which includes the Construction SWPPP  and any associated permits and plans.  o Directing BMP installation, inspection, maintenance, modification, and removal.  o Updating all project drawings and the Construction SWPPP with changes made.  o Completing any sampling requirements including reporting results using electronic  Discharge Monitoring Reports (WebDMR).  o Facilitating, participating in, and taking corrective actions resulting from inspections  performed by outside agencies or the owner.  o Keeping daily logs and inspection reports. Inspection reports should include:  n Inspection date/time.  n Weather information; general conditions during inspection and approximate  amount of precipitation since the last inspection.  n Visual monitoring results, including a description of discharged stormwater.  The presence of suspended sediment, turbid water, discoloration, and oil  sheen shall be noted, as applicable.  n Any water quality monitoring performed during inspection.  n General comments and notes, including a brief description of any BMP repairs,  maintenance or installations made as a result of the inspection.  n A summary or list of all BMPs implemented, including observations of all ESC  structures or practices. The following shall be noted:  1. Locations of BMPs inspected.  2. Locations of BMPs that need maintenance.  3. Locations of BMPs that failed to operate as designed or intended.  4. Locations of where additional or different BMPs are required. BMP C162: Scheduling Purpose Sequencing a construction project can reduce the amount and duration of soil exposed to erosion  by wind, rain, runoff, and vehicle tracking. Conditions of Use The construction sequence schedule is an orderly listing of all major land-disturbing activities  together with the necessary erosion and sediment control (ESC) measures planned for the  2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 372Page 48 of 140 project. This type of schedule guides the contractor on work to be done before other work is star- ted so that serious erosion and sedimentation problems can be avoided. Following a specified work schedule that coordinates the timing of land-disturbing activities and  the installation of control measures is perhaps the most cost-effective way of controlling erosion  during construction. The removal of ground cover leaves a site vulnerable to erosion. Con- struction sequencing that limits land clearing, provides timely installation of ESC BMPs, and  restores protective cover quickly can significantly reduce the erosion potential of a site. Design Considerations  l Minimize construction during rainy periods.  l Schedule projects to disturb only small portions of the site at any one time. Complete grad- ing as soon as possible. Immediately stabilize the disturbed portion before grading the next  portion. Practice staged seeding in order to revegetate cut and fill slopes as the work pro- gresses. II-4.3 Construction Runoff BMPs BMP C200: Interceptor Dike and Swale Purpose Provide a dike of compacted soil or a swale at the top or base of a disturbed slope or along the  perimeter of a disturbed construction area to convey stormwater. Use the dike and/or swale to  intercept the runoff from unprotected areas and direct it to areas where erosion can be controlled.  This can prevent storm runoff from entering the work area or sediment-laden runoff from leaving  the construction site. Conditions of Use Use an interceptor dike or swale where runoff from an exposed site or disturbed slope must be  conveyed to an erosion control BMP that can safely convey the stormwater.  l Locate upslope of a construction site to prevent runoff from entering the disturbed area.  l When placed horizontally across a disturbed slope, it reduces the amount and velocity of  runoff flowing down the slope.  l Locate downslope to collect runoff from a disturbed area and direct it to a sediment trapping  BMP (e.g. BMP C240: Sediment Trap or BMP C241: Sediment Pond (Temporary)). Design and Installation Specifications  l Dike and/or swale and channel must be stabilized with temporary or permanent vegetation  or other channel protection during construction.  l Steep grades require channel protection and check dams. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 373Page 49 of 140 project. This type of schedule guides the contractor on work to be done before other work is star- ted so that serious erosion and sedimentation problems can be avoided. Following a specified work schedule that coordinates the timing of land-disturbing activities and  the installation of control measures is perhaps the most cost-effective way of controlling erosion  during construction. The removal of ground cover leaves a site vulnerable to erosion. Con- struction sequencing that limits land clearing, provides timely installation of ESC BMPs, and  restores protective cover quickly can significantly reduce the erosion potential of a site. Design Considerations  l Minimize construction during rainy periods.  l Schedule projects to disturb only small portions of the site at any one time. Complete grad- ing as soon as possible. Immediately stabilize the disturbed portion before grading the next  portion. Practice staged seeding in order to revegetate cut and fill slopes as the work pro- gresses. II-4.3 Construction Runoff BMPs BMP C200: Interceptor Dike and Swale Purpose Provide a dike of compacted soil or a swale at the top or base of a disturbed slope or along the  perimeter of a disturbed construction area to convey stormwater. Use the dike and/or swale to  intercept the runoff from unprotected areas and direct it to areas where erosion can be controlled.  This can prevent storm runoff from entering the work area or sediment-laden runoff from leaving  the construction site. Conditions of Use Use an interceptor dike or swale where runoff from an exposed site or disturbed slope must be  conveyed to an erosion control BMP that can safely convey the stormwater.  l Locate upslope of a construction site to prevent runoff from entering the disturbed area.  l When placed horizontally across a disturbed slope, it reduces the amount and velocity of  runoff flowing down the slope.  l Locate downslope to collect runoff from a disturbed area and direct it to a sediment trapping  BMP (e.g. BMP C240: Sediment Trap or BMP C241: Sediment Pond (Temporary)). Design and Installation Specifications  l Dike and/or swale and channel must be stabilized with temporary or permanent vegetation  or other channel protection during construction.  l Steep grades require channel protection and check dams. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 373Page 50 of 140  l Review construction for areas where overtopping may occur.  l Can be used at the top of new fill before vegetation is established.  l May be used as a permanent diversion channel to carry the runoff.  l Contributing area for an individual dike or swale should be one acre or less.  l Design the dike and/or swale to contain flows calculated by one of the following methods:  o Single Event Hydrograph Method: The peak volumetric flow rate calculated using a  10-minute time step from a Type 1A, 10-year, 24-hour frequency storm for the worst- case land cover condition. OR  o Continuous Simulation Method: The 10-year peak flow rate, as determined by an  approved continuous runoff model with a 15-minute time step for the worst-case land  cover condition. Worst-case land cover conditions (i.e. producing the most runoff) should be used for ana- lysis. In most cases, this would be the land cover conditions just prior to final landscaping. Interceptor Dikes Interceptor dikes shall meet the following criteria:  l Top Width: 2 feet minimum.  l Height:  1.5 feet minimum on berm.  l Side Slope: 2H:1V or flatter.  l Grade: Depends on topography; however, dike system minimum is 0.5%, and maximum is  1%.  l Compaction: Minimum of 90% ASTM D698 standard proctor.  l Stabilization: Depends on velocity and reach. Inspect regularly to ensure stability.  l Ground Slopes less than 5%: Seed and mulch applied within 5 days of dike construction  (see BMP C121: Mulching).  l Ground Slopes from 5% to 40%: Dependent on runoff velocities and dike materials. Stab- ilization should be done immediately using either sod or riprap, or other measures to avoid  erosion.  l The upslope side of the dike shall provide positive drainage to the dike outlet. No erosion  shall occur at the outlet. Provide energy dissipation measures as necessary. Sediment- laden runoff must be released through a sediment trapping BMP.  l Minimize construction traffic over temporary dikes. Use temporary cross culverts for chan- nel crossing. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 374Page 51 of 140  l See Table II-4.9: Horizontal Spacing of Interceptor Dikes Along Ground Slope for recom- mended horizontal spacing between dikes. Average Slope Slope Percent Flowpath Length 20H:1V or less 3 - 5%300  feet (10 to 20)H:1V 5 - 10%200  feet (4 to 10)H:1V 10 - 25%100  feet (2 to 4)H:1V 25 - 50%50  feet Table II-4.9: Horizontal Spacing of Interceptor Dikes Along Ground Slope Interceptor Swales Interceptor swales shall meet the following criteria:  l Bottom Width: 2 feet minimum; the cross-section bottom shall be level.  l Depth: 1 foot minimum.  l Side Slope: 2H:1V or flatter.  l Grade: Maximum 5%, with positive drainage to a suitable outlet (such as BMP C241: Sed- iment Pond (Temporary)).  l Stabilization: Seed per BMP C120: Temporary and Permanent Seeding, or BMP C202:  Riprap Channel Lining, 12 inches thick riprap pressed into the bank and extending at least 8  inches vertical from the bottom. Maintenance Standards  l Inspect diversion dikes and interceptor swales once a week and after every rainfall. Imme- diately remove sediment from the flow area.  l Damage caused by construction traffic or other activity must be repaired before the end of  each working day.  l Check outlets and make timely repairs as needed to avoid gully formation. When the area  below the temporary diversion dike is permanently stabilized, remove the dike and fill and  stabilize the channel to blend with the natural surface. BMP C201: Grass-Lined Channels Purpose To provide a channel with a vegetative lining for conveyance of runoff. The purpose of the veget- ative lining is to prevent transport of sediment and erosion. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 375Page 52 of 140 Maintenance Standards Replace the riprap as needed. BMP C203: Water Bars Purpose A water bar is a small ditch or ridge of material that is constructed diagonally across a road or  right-of-way to divert stormwater runoff from the road surface, wheel tracks, or a shallow road  ditch. See Figure II-4.12: Water Bar. Conditions of Use Clearing right-of-way and construction of access for power lines, pipelines, and other similar  installations often require long narrow rights-of-ways over sloping terrain. Disturbance and com- paction promotes gully formation in these cleared strips by increasing the volume and velocity of  runoff. Gully formation may be especially severe in tire tracks and ruts. To prevent gullying, runoff  can often be diverted across the width of the right-of-way to undisturbed areas by using small pre- designed diversions. Give special consideration to each individual outlet area, as well as to the cumulative effect of  added diversions. Use gravel to stabilize the diversion where significant vehicular traffic is anti- cipated. Design and Installation Specifications  l Height: 8-inches minimum, measured from the channel bottom to the ridge top.  l Side slope of channel: 2H:1V maximum; 3H:1V or flatter when vehicles will cross.  l Top width of ridge: 6-inches minimum.  l Locate water bars to use natural drainage systems and to discharge into well vegetated  stable areas.  l See Table II-4.10: Water Bar Spacing Guidelines (continued): Slope Along Road (%) Spacing (ft) < 5 125 5 - 10 100 10 - 20 75 Table II-4.10: Water Bar Spacing Guidelines 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 382Page 53 of 140 Slope Along Road (%) Spacing (ft) 20 - 35 50 >  35 Use  rock lined ditch Table II-4.10: Water Bar Spacing Guidelines (continued)  l Grade of water bar and angle: Select an angle that results in a ditch slope less than 2%.  l Install the water bar as soon as the clearing and grading is complete. When utilities are  being installed, reconstruct the water bar as construction is complete in each section.  l Compact the water bar ridge.  l Stabilize, seed, and mulch the portions that are not subject to traffic. Gravel the areas  crossed by vehicles.  l Note that BMP C208: Triangular Silt Dike (TSD) can be used to create the ridge for the  water bar. Maintenance Standards Periodically inspect water bars for wear, and after every heavy rainfall for wear and/or erosion  damage.  l Immediately remove sediment from the flow area and repair the dike.  l Check outlet areas and make timely repairs as needed.  l When permanent road drainage is established and the area above the temporary water bar  is permanently stabilized, remove the dikes and fill the channel to blend with the natural  ground, and appropriately stabilize the disturbed area. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 383Page 54 of 140 Figure II-4.12: Water Bar 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 384Page 55 of 140 BMP C207: Check Dams Purpose Construction of check dams across a swale or ditch reduces the velocity of concentrated flow and  dissipates energy at the check dam. Conditions of Use Use check dams where temporary or permanent channels are not yet vegetated, channel lining is  infeasible, and/or velocity checks are required.  l Check dams may not be placed in streams unless approved by the State Department of  Fish and Wildlife.   l Check dams may not be placed in wetlands without approval from a permitting agency.  l Do not place check dams below the expected backwater from any salmonid bearing water  between October 1 and May 31 to ensure that there is no loss of high flow refuge habitat for  overwintering juvenile salmonids and emergent salmonid fry. Design and Installation Specifications  l Construct rock check dams from appropriately sized rock. The rock used must be large  enough to stay in place given the expected design flow through the channel. The rock must  be placed by hand or by mechanical means (do not dump the rock to form the dam) to  achieve complete coverage of the ditch or swale and to ensure that the center of the dam is  lower than the edges.  l Check dams may also be constructed of either rock or pea-gravel filled bags. Numerous  new products are also available for this purpose. They tend to be re-usable, quick and easy  to install, effective, and cost efficient.  l Place check dams perpendicular to the flow of water.  l The check dam should form a triangle when viewed from the side. This prevents under- cutting as water flows over the face of the check dam rather than falling directly onto the  ditch bottom.  l Before installing check dams, impound and bypass upstream water flow away from the  work area. Options for bypassing include pumps, siphons, or temporary channels.  l Check dams combined with sumps work more effectively at slowing flow and retaining sed- iment than a check dam alone. A deep sump should be provided immediately upstream of  the check dam.  l In some cases, if carefully located and designed, check dams can remain as permanent  installations with very minor regrading. They may be left as either spillways, in which case  accumulated sediment would be graded and seeded, or as check dams to prevent further  sediment from leaving the site. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 395Page 56 of 140  l The maximum spacing between check dams shall be such that the downstream toe of the  upstream dam is at the same elevation as the top of the downstream dam.  l Keep the maximum height at 2 feet at the center of the check dam.  l Keep the center of the check dam at least 12 inches lower than the outer edges at natural  ground elevation.  l Keep the side slopes of the check dam at 2H:1V or flatter.  l Key the stone into the ditch banks and extend it beyond the abutments a minimum of 18  inches to avoid washouts from overflow around the dam.  l Use filter fabric foundation under a rock or sand bag check dam. If a blanket ditch liner is  used, filter fabric is not necessary. A piece of organic or synthetic blanket cut to fit will also  work for this purpose.  l In the case of grass-lined ditches and swales, all check dams and accumulated sediment  shall be removed when the grass has matured sufficiently to protect the ditch or swale -  unless the slope of the swale is greater than 4%. The area beneath the check dams shall be  seeded and mulched immediately after dam removal.  l Ensure that channel appurtenances, such as culvert entrances below check dams, are not  subject to damage or blockage from displaced stones.   l See Figure II-4.16: Rock Check Dam. Maintenance Standards Check dams shall be monitored for performance and sediment accumulation during and after  each rainfall that produces runoff. Sediment shall be removed when it reaches one half the sump  depth.  l Anticipate submergence and deposition above the check dam and erosion from high flows  around the edges of the dam.  l If significant erosion occurs between dams, install a protective riprap liner in that portion of  the channel. See BMP C202: Riprap Channel Lining. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did  not pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jur- isdictions may choose not to accept these products, or may require additional testing prior to con- sideration for local use. Products that Ecology has approved as functionally equivalent are  available for review on Ecology’s website at:  https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per- mittee-guidance-resources/Emerging-stormwater-treatment-technologies 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 396Page 57 of 140 Figure II-4.16: Rock Check Dam 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 397Page 58 of 140  o For a 5 to 10 fps discharge velocity at the outlet, use 24-inch to 48-inch riprap. Min- imum thickness is 2 feet.  o For outlets at the base of steep slope pipes (pipe slope greater than 10 percent), use  an engineered energy dissipator.  o Filter fabric or erosion control blankets should always be used under riprap to prevent  scour and channel erosion. See BMP C122: Nets and Blankets.  l Bank stabilization, bioengineering, and habitat features may be required for disturbed  areas. This work may require a Hydraulic Project Approval (HPA) from the Washington  State Department of Fish and Wildlife. See I-2.14 Hydraulic Project Approvals. Maintenance Standards  l Inspect and repair as needed.  l Add rock as needed to maintain the intended function.  l Clean energy dissipator if sediment builds up. BMP C220: Inlet Protection Purpose Inlet protection prevents coarse sediment from entering drainage systems prior to permanent sta- bilization of the disturbed area. Conditions of Use Use inlet protection at inlets that are operational before permanent stabilization of the disturbed  areas that contribute runoff to the inlet. Provide protection for all storm drain inlets downslope and  within 500 feet of a disturbed or construction area, unless  those inlets are preceded by a sediment  trapping BMP. Also consider inlet protection for lawn and yard drains on new home construction. These small  and numerous drains coupled with lack of gutters can add significant amounts of sediment into the  roof drain system. If possible, delay installing lawn and yard drains until just before landscaping,  or cap these drains to prevent sediment from entering the system until completion of landscaping.  Provide 18-inches of sod around each finished lawn and yard drain. Table II-4.11: Storm Drain Inlet Protection lists several options for inlet protection. All of the meth- ods for inlet protection tend to plug and require a high frequency of maintenance. Limit con- tributing drainage areas for an individual inlet to one acre or less. If possible, provide emergency  overflows with additional end-of-pipe treatment where stormwater ponding would cause a hazard. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 400Page 59 of 140 Type of Inlet Pro- tection Emergency Overflow Applicable for Paved / Earthen Surfaces Conditions of Use Drop Inlet Protection Excavated  drop  inlet protection Yes, temporary  flooding may   occur Earthen Applicable for heavy flows. Easy   to maintain. Large area requirement:   30'x30'/acre Block  and gravel  drop inlet pro- tection Yes Paved or Earthen Applicable for heavy  concentrated flows.  Will not pond. Gravel and wire  drop inlet pro- tection No Paved or Earthen Applicable for  heavy concentrated flows.  Will pond. Can withstand traffic. Catch  basin filters Yes Paved or Earthen Frequent maintenance  required. Curb Inlet Protection Curb  inlet pro- tection with  wooden weir Small capacity  overflow Paved Used for sturdy, more compact  install- ation. Block and gravel  curb inlet pro- tection Yes Paved Sturdy, but  limited filtration. Culvert Inlet Protection Culvert  inlet sed- iment trap N/A N/A 18 month expected life. Table II-4.11: Storm Drain Inlet Protection Design and Installation Specifications Excavated Drop Inlet Protection Excavated drop inlet protection consists of an excavated impoundment around the storm drain  inlet. Sediment settles out of the stormwater prior to entering the storm drain. Design and install- ation specifications for excavated drop inlet protection include:  l Provide a depth of 1 to 2 feet as measured from the crest of the inlet structure.  l Side slopes of excavation should be no steeper than 2H:1V.  l Minimum volume of excavation is 35 cubic yards.  l Shape the excavation to fit the site, with the longest dimension oriented toward the longest  inflow area.  l Install provisions for draining to prevent standing water.  l Clear the area of all debris. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 401Page 60 of 140  l Grade the approach to the inlet uniformly.  l Drill weep holes into the side of the inlet.  l Protect weep holes with screen wire and washed aggregate.  l Seal weep holes when removing structure and stabilizing area.  l Build a temporary dike, if necessary, to the down slope side of the structure to prevent  bypass flow. Block and Gravel Filter A block and gravel filter is a barrier formed around the inlet with standard concrete blocks and  gravel. See Figure II-4.17: Block and Gravel Filter. Design and installation specifications for block  and gravel filters include:  l Provide a height of 1 to 2 feet above the inlet.  l Recess the first row of blocks 2-inches into the ground for stability.  l Support subsequent courses by placing a pressure treated wood (2x4) through the block  opening.  l Do not use mortar.  l Lay some blocks in the bottom row on their side to allow for dewatering the pool.  l Place hardware cloth or comparable wire mesh with 0.5-inch openings over all block open- ings.  l Place gravel to just below the top of blocks on slopes of 2H:1V or flatter.  l An alternative design is a gravel berm surrounding the inlet, as follows:  o Provide a slope of 3H:1V on the upstream side of the berm.  o Provide a slope of 2H:1V on the downstream side of the berm.  o Provide a 1-foot wide level rock area between the gravel berm and the inlet.  o Use rocks 3 inches in diameter or larger on the upstream slope of the berm.  o Use gravel 0.5 to 0.75 inch at a minimum thickness of 1-foot on the downstream  slope of the berm. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 402Page 61 of 140 Figure II-4.17: Block and Gravel Filter 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 403Page 62 of 140 Gravel and Wire Mesh Filter Gravel and wire mesh filters are gravel barriers placed over the top of the inlet. This method does  not provide an overflow. Design and installation specifications for gravel and wire mesh filters  include:  l Use a hardware cloth or comparable wire mesh with 0.5 inch openings.  o Place wire mesh over the drop inlet so that the wire extends a minimum of 1-foot bey- ond each side of the inlet structure.  o Overlap the strips if more than one strip of mesh is necessary.  l Place coarse aggregate over the wire mesh.  o Provide at least a 12-inch depth of aggregate over the entire inlet opening and extend  at least 18-inches on all sides. Catch Basin Filters Catch  basin filters are designed by manufacturers for construction sites. The limited sediment stor- age capacity increases the amount of inspection and maintenance required, which may be daily  for heavy sediment loads. To reduce maintenance requirements, combine a catch  basin filter with  another type of inlet protection. This type of inlet protection provides flow bypass without overflow  and therefore may be a better method for inlets located along active rights-of-way. Design and  installation specifications for catch basin filters include:  l Provides 5 cubic feet of storage.  l Requires dewatering provisions.  l Provides a high-flow bypass that will not clog under normal use at a construction site.  l Insert the catch  basin filter in the catch  basin just below the grating. Curb Inlet Protection with Wooden Weir Curb inlet protection with wooden weir is an option that consists of a barrier formed around a curb  inlet with a wooden frame and gravel. Design and installation specifications for curb inlet pro- tection with wooden weirs include:  l Use wire mesh with 0.5 inch openings.  l Use extra strength filter cloth.  l Construct a frame.  l Attach the wire and filter fabric to the frame.  l Pile coarse washed aggregate against the wire and fabric.  l Place weight on the frame anchors. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 404Page 63 of 140 Block and Gravel Curb Inlet Protection Block and gravel curb inlet protection is a barrier formed around a curb inlet with concrete blocks  and gravel. See Figure II-4.18: Block and Gravel Curb Inlet Protection. Design and installation spe- cifications for block and gravel curb inlet protection include:  l Use wire mesh with 0.5 inch openings.  l Place two concrete blocks on their sides abutting the curb at either side of the inlet opening.  These are spacer blocks.  l Place a 2x4 stud through the outer holes of each spacer block to align the front blocks.  l Place blocks on their sides across the front of the inlet and abutting the spacer blocks.  l Place wire mesh over the outside vertical face.  l Pile coarse aggregate against the wire to the top of the barrier. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 405Page 64 of 140 Figure II-4.18: Block and Gravel Curb Inlet Protection 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 406Page 65 of 140 Curb and Gutter Sediment Barrier A curb and gutter sediment barrier is a sandbag or rock berm (riprap and aggregate) 3 feet high  and 3 feet wide in a horseshoe shape. See Figure II-4.19: Curb and Gutter Barrier. Design and  installation specifications for curb and gutter sediment barriers include:  l Construct a horseshoe shaped berm, faced with coarse aggregate if using riprap, 3 feet  high and 3 feet wide, at least 2 feet from the inlet.  l Construct a horseshoe shaped sedimentation trap on the upstream side of the berm. Size  the trap to sediment trap standards for protecting a culvert inlet. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 407Page 66 of 140 Figure II-4.19: Curb and Gutter Barrier 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 408Page 67 of 140 Maintenance Standards  l Inspect all forms of inlet protection frequently, especially after storm events. Clean and  replace clogged catch basin filters. For rock and gravel filters, pull away the rocks from the  inlet and clean or replace. An alternative approach would be to use the clogged rock as fill  and put fresh rock around the inlet.  l Do not wash sediment into storm drains while cleaning. Spread all excavated material  evenly over the surrounding land area or stockpile and stabilize as appropriate. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did  not pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jur- isdictions may choose not to accept these products, or may require additional testing prior to con- sideration for local use. Products that Ecology has approved as functionally equivalent are  available for review on Ecology’s website at:  https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per- mittee-guidance-resources/Emerging-stormwater-treatment-technologies BMP C231: Brush Barrier Purpose The purpose of brush barriers is to reduce the transport of coarse sediment from a construction  site by providing a temporary physical barrier to sediment and reducing the runoff velocities of  overland flow. Conditions of Use  l Brush barriers may be used downslope of disturbed areas that are less than one-quarter  acre.  l Brush barriers are not intended to treat concentrated flows, nor are they intended to treat  substantial amounts of overland flow. Any concentrated flows must be directed to a sed- iment trapping BMP. The only circumstance in which overland flow can be treated solely by  a brush barrier, rather than by a sediment trapping BMP, is when the area draining to the  barrier is small.  l Brush barriers should only be installed on contours. Design and Installation Specifications  l Height: 2 feet (minimum) to 5 feet (maximum).  l Width: 5 feet at base (minimum) to 15 feet (maximum). 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 409Page 68 of 140 BMP C233: Silt Fence Purpose Silt fence reduces the transport of coarse sediment from a construction site by providing a tem- porary physical barrier to sediment and reducing the runoff velocities of overland flow. Conditions of Use Silt fence may be used downslope of all disturbed areas.  l Silt fence shall prevent sediment carried by runoff from going beneath, through, or over the  top of the silt fence, but shall allow the water to pass through the fence.  l Silt fence is not intended to treat concentrated flows, nor is it intended to treat substantial  amounts of overland flow. Convey any concentrated flows through the drainage system to a  sediment trapping BMP.  l Do not construct silt fences in streams or use in V-shaped ditches. Silt fences do not  provide an adequate method of silt control for anything deeper than sheet or overland flow. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 414Page 69 of 140 Figure II-4.22: Silt Fence 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 415Page 70 of 140 Design and Installation Specifications  l Use in combination with other construction stormwater BMPs.  l Maximum slope steepness (perpendicular to the silt fence line) 1H:1V.  l Maximum sheet or overland flow path length to the silt fence of 100 feet.  l Do not allow flows greater than 0.5 cfs.  l Use geotextile fabric that meets the following standards. All geotextile properties listed  below are minimum average roll values (i.e. the test result for any sampled roll in a lot shall  meet or exceed the values shown in Table II-4.12: Geotextile Fabric Standards for Silt  Fence): Geotextile Property Minimum Average Roll Value Polymeric  Mesh AOS  (ASTM D4751) 0.60 mm maximum for slit film  woven (#30 sieve).  0.30 mm  maximum for all other geotextile types (#50 sieve).  0.15 mm minimum for all fabric types (#100 sieve). Water  Permittivity  (ASTM D4491) 0.02 sec-1 minimum Grab  Tensile Strength  (ASTM D4632) 180 lbs minimum for extra  strength fabric.  100 lbs  minimum for standard strength fabric. Grab Tensile Strength  (ASTM D4632) 30% maximum Ultraviolet  Resistance  (ASTM D4355) 70%  minimum Table II-4.12: Geotextile Fabric Standards for Silt Fence  l Support standard strength geotextiles with wire mesh, chicken wire, 2-inch x 2-inch wire,  safety fence, or jute mesh to increase the strength of the geotextile. Silt fence materials are  available that have synthetic mesh backing attached.  l Silt fence material shall contain ultraviolet ray inhibitors and stabilizers to provide a min- imum of 6 months of expected usable construction life at a temperature range of 0°F to  120°F.  l 100% biodegradable silt fence is available that is strong, long lasting, and can be left in  place after the project is completed, if permitted by the local jurisdiction.  l Refer to Figure II-4.22: Silt Fence for standard silt fence details. Include the following Stand- ard Notes for silt fence on construction plans and specifications:  1. The Contractor shall install and maintain temporary silt fences at the locations shown  in the Plans. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 416Page 71 of 140  2. Construct silt fences in areas of clearing, grading, or drainage prior to starting those  activities.  3. The silt fence shall have a 2-foot min. and a 2.5-feet max. height above the original  ground surface.  4. The geotextile fabric shall be sewn together at the point of manufacture to form fabric  lengths as required. Locate all sewn seams at support posts. Alternatively, two sec- tions of silt fence can be overlapped, provided  that the overlap is long enough and  that the adjacent silt fence sections are close enough together to prevent silt laden  water from escaping through the fence at the overlap.  5. Attach the geotextile fabric on the up-slope side of the posts and secure with staples,  wire, or in accordance with the manufacturer's recommendations. Attach the geo- textile fabric to the posts in a manner that reduces the potential for tearing.  6. Support the geotextile fabric with wire or plastic mesh, dependent on the properties of  the geotextile selected for use. If wire or plastic mesh is used, fasten the mesh  securely to the up-slope side of the posts with the geotextile fabric up-slope of the  mesh.  7. Mesh support, if used, shall consist of steel wire with a maximum mesh spacing of 2- inches, or a prefabricated polymeric mesh. The strength of the wire or polymeric  mesh shall be equivalent to or greater than 180 lbs grab tensile strength. The poly- meric mesh must be as resistant to the same level of ultraviolet radiation as the geo- textile fabric it supports.  8. Bury the bottom of the geotextile fabric 4-inches min. below the ground surface. Back- fill and tamp soil in place over the buried portion of the geotextile fabric, so that no  flow can pass beneath the silt fence and scouring cannot occur. When wire or poly- meric back-up support mesh is used, the wire or polymeric mesh shall extend into the  ground 3-inches min.  9. Drive or place the silt fence posts into the ground 18-inches min. A 12–inch min.  depth is allowed if topsoil or other soft subgrade soil is not present and 18-inches can- not be reached. Increase fence post min. depths by 6 inches if the fence is located on  slopes of 3H:1V or steeper and the slope is perpendicular to the fence. If required  post depths cannot be obtained, the posts shall be adequately secured by bracing or  guying to prevent overturning of the fence due to sediment loading.  10. Use wood, steel or equivalent posts. The spacing of the support posts shall be a max- imum of 6 feet. Posts shall consist of one of the following:  l Wood with minimum dimensions of 2 inches by 2 inches by 3 feet. Wood shall  be free of defects such as knots, splits, or gouges.  l No. 6 steel rebar or larger.  l ASTM A 120 steel pipe with a minimum diameter of 1-inch.  l U, T, L, or C shape steel posts with a minimum weight of 1.35 lbs./ft. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 417Page 72 of 140  l Other steel posts having equivalent strength and bending resistance to the  post sizes listed above.  11. Locate silt fences on contour as much as possible, except at the ends of the fence,  where the fence shall be turned uphill such that the silt fence captures the runoff  water and prevents water from flowing around the end of the fence.  12. If the fence must cross contours, with the exception of the ends of the fence, place  check dams perpendicular to the back of the fence to minimize concentrated flow and  erosion. The slope of the fence line where contours must be crossed shall not be  steeper than 3H:1V.  l Check dams shall be approximately 1 foot deep at the back of the fence. Check  dams shall be continued perpendicular to the fence at the same elevation until  the top of the check dam intercepts the ground surface behind the fence.  l Check dams shall consist of crushed surfacing base course, gravel backfill for  walls, or shoulder ballast. Check dams shall be located every 10 feet along the  fence where the fence must cross contours.  l Refer to Figure II-4.23: Silt Fence Installation by Slicing Method for slicing method details.  The following are specifications for silt fence installation using the slicing method:  1. The base of both end posts must be at least 2 to 4 inches above the top of the geo- textile fabric on the middle posts for ditch checks to drain properly. Use a hand level  or string level, if necessary, to mark base points before installation.  2. Install posts 3 to 4 feet apart in critical retention areas and 6 to 7 feet apart in stand- ard applications.  3. Install posts 24 inches deep on the downstream side of the silt fence, and as close as  possible to the geotextile fabric, enabling posts to support the geotextile fabric from  upstream water pressure.  4. Install posts with the nipples facing away from the geotextile fabric.  5. Attach the geotextile fabric to each post with three ties, all spaced within the top 8  inches of the fabric. Attach each tie diagonally 45 degrees through the fabric, with  each puncture at least 1-inch vertically apart. Each tie should be positioned to hang  on a post nipple when tightening to prevent sagging.  6. Wrap approximately 6 inches of the geotextile fabric around the end posts and  secure with 3 ties.  7. No more than 24 inches of a 36 inch geotextile fabric is allowed above ground level.  8. Compact the soil immediately next to the geotextile fabric with the front wheel of the  tractor, skid steer, or roller exerting at least 60 pounds per square inch. Compact the  upstream side first and then each side twice for a total of four trips. Check and correct  the silt fence installation for any deviation before compaction. Use a flat-bladed  shovel to tuck the fabric deeper into the ground if necessary. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 418Page 73 of 140 Figure II-4.23: Silt Fence Installation by Slicing Method 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 419Page 74 of 140 Maintenance Standards  l Repair any damage immediately.  l Intercept and convey all evident concentrated flows uphill of the silt fence to a sediment trap- ping BMP.  l Check the uphill side of the silt fence for signs of the fence clogging and acting as a barrier  to flow and then causing channelization of flows parallel to the fence. If this occurs, replace  the fence and remove the trapped sediment.  l Remove sediment deposits when the deposit reaches approximately one-third the height of  the silt fence, or install a second silt fence.  l Replace geotextile fabric that has deteriorated due to ultraviolet breakdown. BMP C234: Vegetated Strip Purpose Vegetated strips reduce the transport of coarse sediment from a construction site by providing a  physical barrier to sediment and reducing the runoff velocities of overland flow. Conditions of Use  l Vegetated strips may be used downslope of all disturbed areas.  l Vegetated strips are not intended to treat concentrated flows, nor are they intended to treat  substantial amounts of overland flow. Any concentrated flows must be conveyed through  the drainage system to BMP C241: Sediment Pond (Temporary) or other sediment trapping  BMP. The only circumstance in which overland flow can be treated solely by a vegetated  strip, rather than by a sediment trapping BMP, is when the following criteria are met (see  Table II-4.13: Contributing Drainage Area for Vegetated Strips): Average Contributing Area Slope Average Contributing Area Per- cent Slope Maximum Contributing Area Flowpath Length 1.5H : 1V or flatter 67% or flatter 100 feet 2H : 1V or  flatter 50% or flatter 115 feet 4H : 1V or  flatter 25% or flatter 150  feet 6H : 1V or  flatter 16.7% or flatter 200  feet 10H : 1V or  flatter 10% or flatter 250  feet Table II-4.13: Contributing Drainage Area for Vegetated Strips 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 420Page 75 of 140 Maintenance Standards  l Wattles may require maintenance to ensure they are in contact with soil and thoroughly  entrenched, especially after significant rainfall on steep sandy soils.  l Inspect the slope after significant storms and repair any areas where wattles are not tightly  abutted or water has scoured beneath the wattles. Approved as Functionally Equivalent Ecology has approved products as able to meet the requirements of this BMP. The products did  not pass through the Technology Assessment Protocol – Ecology (TAPE) process. Local jur- isdictions may choose not to accept these products, or may require additional testing prior to con- sideration for local use. Products that Ecology has approved as functionally equivalent are  available for review on Ecology’s website at:  https://ecology.wa.gov/Regulations-Permits/Guidance-technical-assistance/Stormwater-per- mittee-guidance-resources/Emerging-stormwater-treatment-technologies BMP C236: Vegetative Filtration Purpose Vegetative filtration as a BMP is used in conjunction with detention storage in the form of portable  tanks or BMP C241: Sediment Pond (Temporary), BMP C206: Level Spreader, and a pumping  system with surface intake. Vegetative filtration improves turbidity levels of stormwater discharges  by filtering runoff through existing vegetation where undisturbed forest floor duff layer or estab- lished lawn with thatch layer are present.  Vegetative filtration can also be used to infiltrate dewa- tering waste from foundations, vaults, and trenches as long as runoff does not occur. Conditions of Use  l For every 5 acres of disturbed soil, use 1 acre of grass field, farm pasture, or wooded area.  Reduce or increase this area depending on project size, groundwater table height, and  other site conditions.  l Wetlands shall not be used for vegetative filtration.  l Do not use this BMP in areas with a high groundwater table, or in areas that will have a high  seasonal groundwater table during the use of this BMP.  l This BMP may be less effective on soils that prevent the infiltration of the water, such as  hard till.  l Using other effective source control measures throughout a construction site will prevent  the generation of additional highly turbid water and may reduce the time period or area  need for this BMP.  l Stop distributing water into the vegetated filtration area if standing water or erosion results. 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 424Page 76 of 140  l On large projects that phase the clearing of the site, areas retained with native vegetation  may be used as a temporary vegetative filtration area. Design Criteria  l Find land adjacent to the project site that has a vegetated field, preferably a farm field or  wooded area.  l If the site does not contain enough vegetated field area consider obtaining permission from  adjacent landowners (especially for farm fields).  l Install a pump and downstream distribution manifold depending on the project size. Gen- erally, the main distribution line should reach 100 to 200 feet long. Large projects, or pro- jects on tight soil, will require systems that reach several thousand feet long with numerous  branch lines off of the main distribution line.  l The manifold should have several valves, allowing for control over the distribution area in  the field.  l Install several branches of 4 inch diameter schedule 20 polyvinyl chloride (PVC), swaged-fit  common septic tight-lined sewer line, or 6 inch diameter fire hose, which can convey the tur- bid water out to various sections of the field. See Figure II-4.25: Manifold and Branches in a  Wooded, Vegetated Spray Field.  l Determine the branch length based on the field area geography and number of branches.  Typically, branches stretch from 200 feet to several thousand feet. Lay the branches on con- tour with the slope.  l On uneven ground, sprinklers perform well. Space sprinkler heads so that spray patterns  do not overlap.  l On relatively even surfaces, a level spreader using 4 inch diameter perforated pipe may be  used as an alternative option to the sprinkler head setup. Install drain pipe at the highest  point on the field and at various lower elevations to ensure full coverage of the filtration  area. Place the pipe  with the holes up to allow for gentle weeping evenly out all holes.  Lev- eling the pipe by staking and using sandbags may be required.  l To prevent over saturating of the vegetative filtration area, rotate the use of branches or  spray heads. Repeat as needed based on monitoring of the spray field. Average Slope Average Area % Slope Estimated Flowpath Length (ft) 1.5H:1V 67%250 2H:1V 50%200 4H:1V 25%150 6H:1V 16.7%115 10H:1V 10%100 Table II-4.14: Flowpath Guidelines for Vegetative Filtration 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 425Page 77 of 140 Figure II-4.25: Manifold and Branches in a Wooded, Vegetated Spray Field 2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 426Page 78 of 140 Maintenance Standards  l Monitor the spray field on a daily basis to ensure that over saturation of any portion of the  field does not occur at any time. The presence of standing puddles of water or creation of  concentrated flows visually signify that over saturation of the field has occurred.  l Monitor the vegetated spray field all the way down to the nearest surface water, or farthest  spray area, to ensure that the water has not caused overland or concentrated flows, and  has not created erosion around the spray nozzle(s).  l Do not exceed water quality standards for turbidity.  l Ecology recommends that a separate inspection log be developed, maintained, and kept  with the existing site logbook to aid the operator conducting inspections. This separate  “Field Filtration Logbook” can also aid in demonstrating compliance with permit conditions.  l Inspect the spray nozzles daily, at a minimum, for leaks and plugging from sediment  particles.  l If erosion, concentrated flows, or over saturation of the field occurs, rotate the use of  branches or spray heads or move the branches to a new field location.  l Check all branches and the manifold for unintended leaks. BMP C240: Sediment Trap Purpose A sediment trap is a small temporary ponding area with a gravel outlet used to collect and store  sediment from sites during construction. Sediment traps, along with other perimeter controls, shall  be installed before any land disturbance takes place in the contributing drainage area. Conditions of Use  l Sediment traps are intended for use on sites where the contributing drainage area is less  than 3 acres, with no unusual drainage features, and a projected build-out time of 6 months  or less. The sediment trap is a temporary measure (with a design life of approximately 6  months) and shall be maintained until the contributing drainage area is permanently pro- tected against erosion by vegetation and/or structures.  l Sediment traps are only effective in removing sediment down to about the medium silt size  fraction. Runoff with sediment of finer grades (fine silt and clay) will pass through untreated,  emphasizing the need to control erosion to the maximum extent first.  l Projects that are constructing permanent Flow Control BMPs, or permanent Runoff Treat- ment BMPs that use ponding for treatment, may use the rough-graded or final-graded per- manent BMP footprint for the temporary sediment trap. When permanent BMP footprints  are used as temporary sediment traps, the surface area requirement of the sediment trap  must be met. If the surface area requirement of the sediment trap is larger than the surface  area of the permanent BMP, then the sediment trap shall be enlarged beyond the  2024 Stormwater Management Manual for Western Washington Volume II -Chapter 4 -Page 427Page 79 of 140 APPENDIX “B” FEMA MAP Page 80 of 140 Page 81 of 140 APPENDIX “C” WETLAND DELINEATION AND RATING REPORT Page 82 of 140 Page 83 of 140 Page 84 of 140 Page 85 of 140 Page 86 of 140 Page 87 of 140 Page 88 of 140 Page 89 of 140 Page 90 of 140 Page 91 of 140 Page 92 of 140 Page 93 of 140 Page 94 of 140 Page 95 of 140 Page 96 of 140 Page 97 of 140 Page 98 of 140 Page 99 of 140 Page 100 of 140 Page 101 of 140 Page 102 of 140 Page 103 of 140 Page 104 of 140 Page 105 of 140 Page 106 of 140 Page 107 of 140 Page 108 of 140 Page 109 of 140 Page 110 of 140 Page 111 of 140 Page 112 of 140 Page 113 of 140 Page 114 of 140 Page 115 of 140 Page 116 of 140 Page 117 of 140 Page 118 of 140 Page 119 of 140 Page 120 of 140 Page 121 of 140 Page 122 of 140 Page 123 of 140 Page 124 of 140 Page 125 of 140 Page 126 of 140 Page 127 of 140 Page 128 of 140 Page 129 of 140 Page 130 of 140 APPENDIX “D” NRCS SOIL MAP Page 131 of 140 Soil Map—Thurston County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 9/4/2024 Page 1 of 3 51 9 7 5 5 0 51 9 7 5 8 0 51 9 7 6 1 0 51 9 7 6 4 0 51 9 7 6 7 0 51 9 7 7 0 0 51 9 7 7 3 0 51 9 7 7 6 0 51 9 7 7 9 0 51 9 7 8 2 0 51 9 7 5 5 0 51 9 7 5 8 0 51 9 7 6 1 0 51 9 7 6 4 0 51 9 7 6 7 0 51 9 7 7 0 0 51 9 7 7 3 0 51 9 7 7 6 0 51 9 7 7 9 0 51 9 7 8 2 0 531440 531470 531500 531530 531560 531590 531620 531650 531440 531470 531500 531530 531560 531590 531620 531650 46° 55' 59'' N 12 2 ° 3 5 ' 1 3 ' ' W 46° 55' 59'' N 12 2 ° 3 5 ' 2 ' ' W 46° 55' 50'' N 12 2 ° 3 5 ' 1 3 ' ' W 46° 55' 50'' N 12 2 ° 3 5 ' 2 ' ' W N Map projection: Web Mercator Corner coordinates: WGS84 Edge tics: UTM Zone 10N WGS84 0 50 100 200 300 Feet 0 20 40 80 120 Meters Map Scale: 1:1,460 if printed on A portrait (8.5" x 11") sheet. Soil Map may not be valid at this scale. Page 132 of 140 MA P L E G E N D MA P I N F O R M A T I O N Ar e a o f I n t e r e s t ( A O I ) Ar e a o f I n t e r e s t ( A O I ) So i l s So i l M a p U n i t P o l y g o n s So i l M a p U n i t L i n e s So i l M a p U n i t P o i n t s Sp e c i a l P o i n t F e a t u r e s Bl o w o u t Bo r r o w P i t Cl a y S p o t Cl o s e d D e p r e s s i o n Gr a v e l P i t Gr a v e l l y S p o t La n d f i l l La v a F l o w Ma r s h o r s w a m p Mi n e o r Q u a r r y Mi s c e l l a n e o u s W a t e r Pe r e n n i a l W a t e r Ro c k O u t c r o p Sa l i n e S p o t Sa n d y S p o t Se v e r e l y E r o d e d S p o t Si n k h o l e Sl i d e o r S l i p So d i c S p o t Sp o i l A r e a St o n y S p o t Ve r y S t o n y S p o t We t S p o t Ot h e r Sp e c i a l L i n e F e a t u r e s Wa t e r F e a t u r e s St r e a m s a n d C a n a l s Tr a n s p o r t a t i o n Ra i l s In t e r s t a t e H i g h w a y s US R o u t e s Ma j o r R o a d s Lo c a l R o a d s Ba c k g r o u n d Ae r i a l P h o t o g r a p h y Th e s o i l s u r v e y s t h a t c o m p r i s e y o u r A O I w e r e m a p p e d a t 1: 2 4 , 0 0 0 . Wa r n i n g : S o i l M a p m a y n o t b e v a l i d a t t h i s s c a l e . En l a r g e m e n t o f m a p s b e y o n d t h e s c a l e o f m a p p i n g c a n c a u s e mi s u n d e r s t a n d i n g o f t h e d e t a i l o f m a p p i n g a n d a c c u r a c y o f s o i l li n e p l a c e m e n t . T h e m a p s d o n o t s h o w t h e s m a l l a r e a s o f co n t r a s t i n g s o i l s t h a t c o u l d h a v e b e e n s h o w n a t a m o r e d e t a i l e d sc a l e . Pl e a s e r e l y o n t h e b a r s c a l e o n e a c h m a p s h e e t f o r m a p me a s u r e m e n t s . So u r c e o f M a p : Na t u r a l R e s o u r c e s C o n s e r v a t i o n S e r v i c e We b S o i l S u r v e y U R L : Co o r d i n a t e S y s t e m : We b M e r c a t o r ( E P S G : 3 8 5 7 ) Ma p s f r o m t h e W e b S o i l S u r v e y a r e b a s e d o n t h e W e b M e r c a t o r pr o j e c t i o n , w h i c h p r e s e r v e s d i r e c t i o n a n d s h a p e b u t d i s t o r t s di s t a n c e a n d a r e a . A p r o j e c t i o n t h a t p r e s e r v e s a r e a , s u c h a s t h e Al b e r s e q u a l - a r e a c o n i c p r o j e c t i o n , s h o u l d b e u s e d i f m o r e ac c u r a t e c a l c u l a t i o n s o f d i s t a n c e o r a r e a a r e r e q u i r e d . Th i s p r o d u c t i s g e n e r a t e d f r o m t h e U S D A - N R C S c e r t i f i e d d a t a a s of t h e v e r s i o n d a t e ( s ) l i s t e d b e l o w . So i l S u r v e y A r e a : Th u r s t o n C o u n t y A r e a , W a s h i n g t o n Su r v e y A r e a D a t a : Ve r s i o n 1 7 , A u g 2 9 , 2 0 2 3 So i l m a p u n i t s a r e l a b e l e d ( a s s p a c e a l l o w s ) f o r m a p s c a l e s 1: 5 0 , 0 0 0 o r l a r g e r . Da t e ( s ) a e r i a l i m a g e s w e r e p h o t o g r a p h e d : Ma y 2 6 , 2 0 2 3 — A u g 14 , 2 0 2 3 Th e o r t h o p h o t o o r o t h e r b a s e m a p o n w h i c h t h e s o i l l i n e s w e r e co m p i l e d a n d d i g i t i z e d p r o b a b l y d i f fe r s f r o m t h e b a c k g r o u n d im a g e r y d i s p l a y e d o n t h e s e m a p s . A s a r e s u l t , s o m e m i n o r sh i f t i n g o f m a p u n i t b o u n d a r i e s m a y b e e v i d e n t . So i l M a p — T h u r s t o n C o u n t y A r e a , W a s h i n g t o n Na t u r a l R e s o u r c e s Co n s e r v a t i o n S e r v i c e We b S o i l S u r v e y Na t i o n a l C o o p e r a t i v e S o i l S u r v e y 9/ 4 / 2 0 2 4 Pa g e 2 o f 3 Page 133 of 140 Map Unit Legend Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI 65 McKenna gravelly silt loam, 0 to 5 percent slopes 2.1 19.1% 110 Spanaway gravelly sandy loam, 0 to 3 percent slopes 8.8 79.6% 112 Spanaway stony sandy loam, 0 to 3 percent slopes 0.1 1.3% Totals for Area of Interest 11.0 100.0% Soil Map—Thurston County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 9/4/2024 Page 3 of 3 Page 134 of 140 Thurston County Area, Washington 110—Spanaway gravelly sandy loam, 0 to 3 percent slopes Map Unit Setting National map unit symbol: 2ndb6 Elevation: 330 to 1,310 feet Mean annual precipitation: 35 to 65 inches Mean annual air temperature: 50 degrees F Frost-free period: 150 to 200 days Farmland classification: Prime farmland if irrigated Map Unit Composition Spanaway and similar soils:100 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Spanaway Setting Landform:Terraces, outwash plains Parent material:Volcanic ash over gravelly outwash Typical profile H1 - 0 to 15 inches: gravelly sandy loam H2 - 15 to 20 inches: very gravelly loam H3 - 20 to 60 inches: extremely gravelly sand Properties and qualities Slope:0 to 3 percent Depth to restrictive feature:More than 80 inches Drainage class:Somewhat excessively drained Capacity of the most limiting layer to transmit water (Ksat):High (1.98 to 5.95 in/hr) Depth to water table:More than 80 inches Frequency of flooding:None Frequency of ponding:None Available water supply, 0 to 60 inches: Low (about 3.8 inches) Interpretive groups Land capability classification (irrigated): 3s Land capability classification (nonirrigated): 3s Hydrologic Soil Group: A Ecological site: R002XA006WA - Puget Lowlands Prairie Forage suitability group: Droughty Soils (G002XS401WA) Other vegetative classification: Droughty Soils (G002XS401WA) Map Unit Description: Spanaway gravelly sandy loam, 0 to 3 percent slopes---Thurston County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 9/4/2024 Page 1 of 2 Page 135 of 140 Hydric soil rating: No Data Source Information Soil Survey Area: Thurston County Area, Washington Survey Area Data: Version 17, Aug 29, 2023 Map Unit Description: Spanaway gravelly sandy loam, 0 to 3 percent slopes---Thurston County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 9/4/2024 Page 2 of 2 Page 136 of 140 Thurston County Area, Washington 65—McKenna gravelly silt loam, 0 to 5 percent slopes Map Unit Setting National map unit symbol: 2nd9g Elevation: 50 to 500 feet Mean annual precipitation: 30 to 60 inches Mean annual air temperature: 48 to 52 degrees F Frost-free period: 150 to 180 days Farmland classification: Prime farmland if drained Map Unit Composition Mckenna and similar soils:85 percent Minor components:15 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Mckenna Setting Landform:Depressions, drainageways Parent material:Glacial drift Typical profile H1 - 0 to 9 inches: gravelly silt loam H2 - 9 to 13 inches: gravelly silt loam H3 - 13 to 36 inches: very gravelly loam H4 - 36 to 40 inches: very gravelly loam Properties and qualities Slope:0 to 5 percent Depth to restrictive feature:20 to 39 inches to densic material Drainage class:Poorly drained Capacity of the most limiting layer to transmit water (Ksat):Very low to moderately low (0.00 to 0.06 in/hr) Depth to water table:About 0 to 6 inches Frequency of flooding:None Frequency of ponding:Frequent Available water supply, 0 to 60 inches: Low (about 5.4 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 6w Hydrologic Soil Group: D Ecological site: F002XA007WA - Puget Lowlands Wet Forest Forage suitability group: Wet Soils (G002XS101WA) Other vegetative classification: Wet Soils (G002XS101WA) Hydric soil rating: Yes Map Unit Description: McKenna gravelly silt loam, 0 to 5 percent slopes---Thurston County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 9/4/2024 Page 1 of 2 Page 137 of 140 Minor Components Bellingham, undrained Percent of map unit:5 percent Landform:Depressions Other vegetative classification:Wet Soils (G002XN102WA) Hydric soil rating: Yes Skipopa Percent of map unit:5 percent Other vegetative classification:Seasonally Wet Soils (G002XN202WA) Hydric soil rating: No Norma Percent of map unit:5 percent Landform:Depressions Other vegetative classification:Wet Soils (G002XS101WA) Hydric soil rating: Yes Data Source Information Soil Survey Area: Thurston County Area, Washington Survey Area Data: Version 17, Aug 29, 2023 Map Unit Description: McKenna gravelly silt loam, 0 to 5 percent slopes---Thurston County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 9/4/2024 Page 2 of 2 Page 138 of 140 Thurston County Area, Washington 112—Spanaway stony sandy loam, 0 to 3 percent slopes Map Unit Setting National map unit symbol: 2ndb8 Elevation: 660 to 1,310 feet Mean annual precipitation: 35 to 65 inches Mean annual air temperature: 50 degrees F Frost-free period: 150 to 200 days Farmland classification: Farmland of statewide importance Map Unit Composition Spanaway and similar soils:100 percent Estimates are based on observations, descriptions, and transects of the mapunit. Description of Spanaway Setting Landform:Terraces, outwash plains Parent material:Volcanic ash over gravelly outwash Typical profile H1 - 0 to 16 inches: stony sandy loam H2 - 16 to 22 inches: very gravelly sandy loam H3 - 22 to 60 inches: extremely gravelly sand Properties and qualities Slope:0 to 3 percent Depth to restrictive feature:More than 80 inches Drainage class:Somewhat excessively drained Capacity of the most limiting layer to transmit water (Ksat):High (1.98 to 5.95 in/hr) Depth to water table:More than 80 inches Frequency of flooding:None Frequency of ponding:None Available water supply, 0 to 60 inches: Low (about 4.0 inches) Interpretive groups Land capability classification (irrigated): None specified Land capability classification (nonirrigated): 4s Hydrologic Soil Group: A Ecological site: R002XA006WA - Puget Lowlands Prairie Forage suitability group: Droughty Soils (G002XS401WA) Other vegetative classification: Droughty Soils (G002XS401WA) Map Unit Description: Spanaway stony sandy loam, 0 to 3 percent slopes---Thurston County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 9/4/2024 Page 1 of 2 Page 139 of 140 Hydric soil rating: No Data Source Information Soil Survey Area: Thurston County Area, Washington Survey Area Data: Version 17, Aug 29, 2023 Map Unit Description: Spanaway stony sandy loam, 0 to 3 percent slopes---Thurston County Area, Washington Natural Resources Conservation Service Web Soil Survey National Cooperative Soil Survey 9/4/2024 Page 2 of 2 Page 140 of 140