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D_Drainage Report_251227_v2
DRAINAGE REVIEW REPORT TIR FOR BO DE TEMPLE AT 11410 SE PETROVITSKY DR RENTON WA 98055 2025 DIRECTED DRAINAGE REVIEW BY: KERELLOS YOUSSEF, PE SKYGATE ENGINEERS AND CONSULTANTS | 21619 36TH DR SE, BOTHELL WA 98021 12/22/2025 RECEIVED 12/29/2025 vporter PLANNING DIVISION 1 | P a g e TABLE OF CONTENTS 1 : PROPERTY OWNER INFORMATION…………….…………………… PAGE 2 2 : APPLICANT INFORMATION…………………………………………… PAGE 2 3 : PROJECT OVERVIEW……………..………..…………………………… PAGE 2 4 : EXISTING PROJECT SITE CONDITIONS..……………..……………… PAGE 3 5 : THE PROPOSED PROJECT DESCRIPTION………………………..…… PAGE 6 6 : DRAINAGE ASSASSMENT .…………………………………………….. PAGE 7 7 : THE NINE CORE REQUIREMENTS COMPLIANCE ….………………. PAGE 9 8 : SPECIAL REQUIREMENTS COMPLIANCE …………………………… PAGE 52 APPENDICES APPENDIX A ……… SITE PLAN APPENDIX B ……… WWHM 2012 REPORT APPENDIX C ……… BMP PLAN APPENDIX D ……… CSWPP PLAN APPENDIX E ……… CURRENT SURVEY PLAN APPENDIX F ……… SOIL FEASABILITY STUDY APPENDIX G ……… KING COUNTY iMAP 2 | P a g e 1. PROPERTY OWNER INFORMATION Name: Thich Thanh Tri Project Name: BO DE TEMPLE RENOVATION AND ROOF REPLACEMENT PROJECT Mailing Address: 11410 SE Petrovitsky Rd, Renton, WA 98055 Contact Phone: (206) 349-5104 E-Mail Address: thichthanhtri@yahoo.com 2. APPLICANT INFORMATION Name: Kerellos Youssef Company: Skygate Engineers and Consultants LLC. Mailing Address: 21619 36th DR SE, Bothell, WA 98021 Contact Phone: 425-623-4619 E-Mail Address: kerellos.y@skygatengineering.com 3. PROJECT OVERVIEW At the request of Thich Thanh Tri, Skygate Engineers and Consultants LLC, has prepared a Technical Information Report (TIR) for parcel # 2923059025 in the City of Renton. The subject site is located at 11410 SE Petrovitsky RD Renton, WA 98055 for Church/Welfare/Religious use. The project location and vicinity is shown in Figure 1 below. The purpose of this Technical Information Report (TIR) is to provide the technical information and design analysis required for preparing the drainage design for the proposed project on the subject parcel. The property falls under the authority of The City of Renton that adopted the current 2022 City of Renton Surface Water Design Manual and 2021 King County Surface Water Design Manual (2021 KCSWDM). The proposed project scope is: Remodeling the interior of the single home to change the first floor to the Buddha Hall for Buddha Service, add on the ramp and stairs for the entrance of the first floor, and add on shed on the north side of Existing Temple Building Water coming from the roofs downspouts will be directed to the gravel dispersion trenches BMP. The asphalt Driveways stormwater runoff will be managed by Basic Dispersion-Sheet Flow BMP. 3 | P a g e 4. THE EXISTING PROJECT SITE CONDITION The existing project site condition is asphalt driveway (about 4,988 Square Foot), a shed over a concrete pad (3078 Square Foot), and a Single Family Home (1,345 Square Foot) and Existing Living Quarters (1,108 Square Foot). Deck attached to the houses (1,067 Square foot) The remaining area is vegetated area (26,551 Square Foot). Figure 1 - Existing Project location 4 | P a g e Figure 2 - Existing Project Site The project site currently drains the empty lot through dispersing the stormwater runoff on the existing lot yard. 5 | P a g e 5. THE PROPOSED PROJECT DESCRIPTION The proposed project scope is: Remodeling the interior of the single home to change the first floor to the Buddha Hall for Buddha Service, add on the ramp and stairs for the entrance of the first floor, and add on shed on the north side of Existing Temple Building. The total concrete and asphalt driveway (9,608 Square Foot), and Temple Building (1,345 Square Foot) and Existing Living Quarters (1,108 Square Foot) and the Decks attached to both buildings (1,067 Square Foot). The remaining area is vegetated area (21,931 Square Foot). There is a shed located on Concrete slab with 3,078 Square Foot. The Stormwater runoff from the roofs is proposed to be managed by Dispersion Trenches BMP and the asphalt driveways will be managed by sheet flow dispersion flow. Figure 4 - The Proposed Project Developments 6 | P a g e 6. DRAINAGE ASSESSMENT Project Name: BO DE TEMPLE RENOVATION AND ROOF REPLACEMENT PROJECT Address: 11410 SE Petrovitsky Rd, Renton, WA 98055 The project is located South of Renton on a 0.87-acre lot. The lot is mostly vegetated areas and surrounded by Single Family Houses. The lot is proposed to slopes (slightly) down toward the North East side. The property Zone is R-14. The Temple Building is located on the South side of the property on SE 176th Street. The total lot area of 38,137 square feet, of and the proposed project scope is: Remodeling the interior of the single home to change the first floor to the Buddha Hall for Buddha Service, add on the ramp and stairs for the entrance of the first floor, and add on shed on the north side of Existing Temple Building. The final project concrete and asphalt driveway (about 9,608 Square Foot), a shed over a concrete pad (3078 Square Foot), and proposed Temple Building (1,345 Square Foot) and Existing Living Quarters (1,108 Square Foot) and the attached building decks (1,067 Square Foot). The remaining area is vegetated area (21,931 Square Foot). The total proposed impervious surface is 16,206 square feet. No wetlands or streams are available on the site vicinity within at least 1000 feet radius. No Steep slopes are available on the site lot. A 20-foot building rear and front setback is required and 5-foot side set back as shown on the Site Plan is required. Because the lot is larger than 22,000 square feet, it is subject to the Large Lot BMP Requirements in Appendix C of the Surface Water Design Manual. As mandated by these requirements, all proposed impervious surface (10,487 square feet) is targeted for application of flow control BMPs. To address the requirements for mitigation of target impervious surface, the applicability and feasibility of full dispersion was considered first. The vegetation area to remain is proposed to be 21,931 SF. Meaning that full dispersion could be applicable to up to 3,655 square feet of the target impervious surface (15% of 21,931). However, the minimum required 100 feet of native vegetated flow path segment that has a slope of 15% or flatter is achievable, but the proposed impervious surfaces are 16,206sf. Therefore, full dispersion is not feasible. For the House Roof areas, Stormwater dispersion trenches will be feasible hence it will be the proposed BMP for the roof runoff stormwater. Roofs proposed are the temple building (1,345 Square Foot) and Existing Living Quarters (1,108 Square Foot). The 10-foot trench can manage 1400 sf of roof area. Meaning that two 10 feet trenches will be used to disperse stormwater runoff from the two buildings roofs. The vegetation flow path will be 100 feet. The Slope is 10% (<15%). The Dispersion Trenches BMP is feasible. For the Driveway Basic Dispersion BMP was considered and found feasible for managing the stormwater runoff. 20 feet will be maintained as vegetation flow path to be maintained on the North side of the Asphalt Driveway. Full infiltration of roof runoff was considered next. According to the attached soils report the soil infiltration capacity not enough for the Infiltration BMP. Therefore, full infiltration is not applicable. Permeable pavement was considered for the driveway and parking area, but the Soil Feasibility Study recommended against infiltration BMPs. 7 | P a g e Given the fact that Both Full Dispersion and Full Infiltration BMPs were determined not feasible, a “Directed Drainage Review” will be conducted because the project propose more than 5,000 SF of new/replaced impervious surfaces. The WWHM2012 Hydrology Model initial run showed the 100 years runoff difference between mitigated and predeveloped scenarios less than 0.15 Cubic Feet Per Second (0.063 CFS). Bioretention and Permeable Pavement BMPs will not be feasible due to the soil nature and the limited permeability of the Soil per the attached Soil Report. In order to prevent erosion and trap sediments within the project site, the following BMPs will be used approximately as shown in the ESC details on the CSWPP plan: • Clearing limits will be marked by fencing or other means on the ground. • The driveway will be constructed and graveled immediately. A rocked construction entrance will be placed at the end of the driveway. Cleared areas accepting sheet flow from the driveway and parking area will be seeded and mulched. • Silt fencing will be placed along West site of the site to eliminate any runoff flow outside the property during construction. 8 | P a g e 7. THE NINE CORE REQUIREMENTS COMPLIENCE Core Requirements #1: DISCHARGE AT NATURAL LOCATION 1. There is no concentrated runoff generated by the proposed project, because runoff from the roofs will be managed first through (Dispersion Trenches BMP) and dispersion BMPs will be used to manage the runoff from the proposed driveways. Bottom line, no flow concentrations is anticipated from the project. 2. The project is not located within or adjacent to a Landslide Hazard Drainage Area or drains over the erodible soils of a landslide hazard area with slopes steeper than 15%. Core Requirements #2: OFFSITE ANALYSIS Throughout the 1 mile radius from the site, the following drainage problems are not present: 1. Conveyance system nuisance problem 2. Severe erosion problem 3. Severe flooding problem. No Wetland is located on the property, however, there is a stream and wetland located on the property located on the north side of the property. The stormwater runoff from both the building roofs and the driveways will me managed within the site. Given the fact that the proposed project is for religious use building, no impact on the water quality impact is anticipated from the generated run off from this site. None of the following pollutants will be generated: 1. Bacteria Problem 2. Dissolved Oxygen Problem 3. Temperature Problem 4. Metals Problem 5. Phosphorus Problem 6. Turbidity Problem 7. High pH Problem An abbreviated Level 1 downstream analysis has been completed for the project as follows: Task 1 – Define the Study Area The study area shall extend ¼-mile downstream of the proposed project discharge location. The study area shall also extend downstream to a point on the drainage system where the proposed project site constitutes a minimum of 15% of the total tributary drainage area, but no less than ¼-mile. 9 | P a g e Task 2 – Review all available Information on the Study Area The information used for completing this downstream analysis included the following resources and documents: - Topographic Survey Mapping (Attached) - Soil Report (Attached) - City of Renton COR MAPs (Attached). Task 3 – Field Inspect the Study Area The Project Site was visited in December. 2025. The onsite and downstream flow-path conditions were reviewed. (See drainage description in Task 4 below). Task 4 – Drainage Description Upstream Analysis There is no significant upstream tributary to the subject project. There is no wetlands in the upstream of the project site. The project is surrounded by Single Family Houses on the North, South and West sides. Downstream Analysis There is a Wetland and a stream on the downstream of the project but not on the same property. They are located on the property on the north side of the subject property. Task 5 – Mitigation of Existing or Potential Problems No existing or potential flow-control problems are anticipated. Core Requirements #3: FLOW CONTROL FACILITIES The proposed project is exempted from the flow control facility requirements as per (2021 Surface Water Design Manual) Section 1.2.3.2 FLOW CONTROL FACILITY IMPLEMENTATION REQUIREMENTS: E.5. “Compensatory mitigation by a flow control facility must be provided so that the net effect at the point of convergence downstream is the same with or without the bypass. This mitigation may be waived if the existing site conditions 100-year peak discharge from the area of bypassed target surfaces is increased by no more than 0.1 cfs (modeled using 1 hour time steps) or no more than 0.15 cfs (modeled using 15 minute time steps) and flow control BMPs as detailed in Appendix C are applied to all impervious surfaces within the area of bypassed target surfaces. “ Attached is the WWHM2012 Modelling Report that shows the 100-year peak discharge is increased less than 0.15 cfs (0.063 cfs). Core Requirements #4: CONVEYANCE SYSTEM Not applicable. Existing offsite conveyance systems need not be analyzed for conveyance capacity. 10 | P a g e Core Requirements #5: CONSTRUCTION STORMWATER POLLUTION PREVENTION CSWPP Plan will be attached to this report. It includes Erosion and Sedimentation Control Plan (ESC) and Stormwater Pollution and Spill measures. ESC MEASURES Each of the following categories of ESC have been considered for application to the project site as detailed in the Erosion and Sediment Control (ESC) Standards located in the King County Construction Stormwater Pollution Prevention Standards adopted as Appendix D. 1. Clearing Limits PLASTIC OR METAL FENCE (High Visibility Fence) Purpose Fencing is intended to (1) restrict clearing to approved limits; (2) prevent disturbance of critical areas, their buffers, and other areas required to be left undisturbed; (3) limit construction traffic to designated construction entrances or roads; and (4) protect areas where marking with survey tape may not provide adequate protection. Conditions of Use To establish clearing limits, plastic or metal fence may be used: 1. At the boundary of critical areas, their buffers, and other areas required to be left uncleared. 2. As necessary to control vehicle access to and on the site (see Sections D.2.1.4.1 and D.2.1.4.2). Design and Installation Specifications 1. The fence shall be designed and installed according to the manufacturer's specifications. 2. The fence shall be at least 3 feet high and must be highly visible. 3. The fence shall not be wired or stapled to trees. Maintenance Requirements 1. If the fence has been damaged or visibility reduced, it shall be repaired or replaced immediately and visibility restored. 2. Disturbance of a critical area, critical area buffer, native growth retention area, or any other area required to be left undisturbed shall be reported to the County for resolution. 2. Cover Measures Use Plastic Cover on Undisturbed Soils 11 | P a g e Temporary and permanent cover measures shall be provided to protect all disturbed areas, including the faces of cut and fill slopes. Temporary cover shall be installed if an area is to remain unworked for more than seven days during the dry season (May 1 to September 30) or for more than two consecutive working days during the wet season (October 1 to April 30). These time limits may be relaxed if an area poses a low risk of erosion due to soil type, slope gradient, anticipated weather conditions, or other factors. Conversely, the County may reduce these time limits if site conditions warrant greater protection (e.g., adjacent to significant aquatic resources or highly erosive soils) or if significant precipitation (see Section D.2.4.2) is expected. Any area to remain unworked for more than 30 days shall be seeded or sodded, unless the County determines that winter weather makes vegetation establishment infeasible. During the wet season, slopes and stockpiles at 3H:1V or steeper and with more than ten feet of vertical relief shall be covered if they are to remain unworked for more than 12 hours. Also during the wet season, the material necessary to cover all disturbed areas must be stockpiled on site. The intent of these cover requirements is to have as much area as possible covered during any period of precipitation. Purpose: The purpose of covering exposed soils is to prevent erosion, thus reducing reliance on less effective methods that remove sediment after it is entrained in runoff. Cover is the only practical method of reducing turbidity in runoff. Structural measures, such as silt fences and sediment ponds, are only capable of removing coarse particles and in most circumstances have little to no effect on turbidity. When to Install: Any exposed soils that will remain unworked for more than the time limit set above shall be covered by the end of the working day. If the exposed area is to remain unworked for more than 30 days, the area shall be seeded with the temporary seed mix or an equivalent mix that will provide rapid protection (see Section D.2.1.2.6). If the disturbed area is to remain unworked for a year or more or if the area has reached final grade, permanent seed mix or an equivalent mix shall be applied. Measures to Use: Cover methods include the use of surface roughening, mulch, erosion control nets and blankets, plastic covering, seeding, and sodding. Mulch and plastic sheeting are primarily intended to protect disturbed areas for a short period of time, typically days to a few months. Seeding and sodding are measures for areas that are to remain unworked for months. Erosion nets and blankets are to be used in conjunction with seeding steep slopes. The choice of measures is left to the designer; however, there are restrictions on the use of these methods, which are listed in the "Conditions of Use" and the "Design and Installation Specifications" sections for each measure. The methods listed are by no means exhaustive. Variations on the standards presented here are encouraged if other cost- effective products or methods provide substantially equivalent or superior performance. Also, the details of installation can, and should, vary with the site conditions. A useful reference on the application of cover measures in the Puget Sound area is Improving the Cost Effectiveness of Highway Construction Site Erosion and Pollution Control, Horner, Guedry, and Kortenhof (1990). Purpose Plastic covering provides immediate, short-term erosion protection to slopes and disturbed areas. Conditions of Use 1. Plastic covering may be used on disturbed areas that require cover measures for less than 30 days. 2. Plastic is particularly useful for protecting cut and fill slopes and stockpiles. Note: The relatively rapid breakdown of most polyethylene sheeting makes it unsuitable for long-term applications. 3. Clear plastic sheeting may be used over newly-seeded areas to create a greenhouse effect and encourage grass growth. Clear plastic should not be used for this purpose during the summer months because the resulting high temperatures can kill the grass. 4. Due to rapid runoff caused by plastic sheeting, this method shall not be used upslope of areas that might be adversely impacted by concentrated runoff. Such areas include steep and/or unstable slopes. Note: There have been many problems with plastic, usually attributable to poor installation and maintenance. However, the material itself can cause problems, even when correctly installed and maintained, because it generates high-velocity runoff and breaks down quickly due to ultraviolet radiation. In addition, if the plastic is not completely removed, it can clog drainage system inlets and outlets. It is highly recommended that alternatives to plastic sheeting be used whenever possible and that its use be limited. Design and Installation Specifications 1. See Figure D.2.1.2.D for details. 2. Plastic sheeting shall have a minimum thickness of 0.06 millimeters. 12 | P a g e 3. 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 for Plastic Covering 1. Torn sheets must be replaced and open seams repaired. 2. If the plastic begins to deteriorate due to ultraviolet radiation, it must be completely removed and replaced. 3. When the plastic is no longer needed, it shall be completely removed. 3. Perimeter Protection Perimeter protection to filter sediment from sheetwash shall be located downslope of all disturbed areas and shall be installed prior to upslope grading. Perimeter protection includes the use of vegetated strips as well as, constructed measures, such as silt fences, fiber rolls, sand/gravel barriers, brush or rock filters, triangular silt dikes and other methods. During the wet season, 50 linear feet of silt fence (and the necessary stakes) per acre of disturbed area must be stockpiled on site. Purpose: The purpose of perimeter protection is to reduce the amount of sediment transported beyond the disturbed areas of the construction site. Perimeter protection is primarily a backup means of sediment control. Most, if not all, sediment-laden water is to be treated in a sediment trap or pond. The only circumstances in which perimeter control is to be used as a primary means of sediment removal is when the catchment is very small (see below). When to Install: Perimeter protection is to be installed prior to any upslope clearing and grading. Measures to Use: The above measures may be used interchangeably and are not the only perimeter protection measures available. If surface water is collected by an interceptor dike or swale and routed to a sediment pond or trap, there may be no need for the perimeter protection measures specified in this section. Criteria for Use as Primary Treatment: At the boundary of a site, perimeter protection may be used as the sole form of treatment when the flowpath meets the criteria listed below. If these criteria are not met, perimeter protection shall only be used as a backup to a sediment trap or pond. Average Slope Slope Percent Flowpath Length 1.5H:1V or less 67% or less 100 feet 2H:1V or less 50% or less 115 feet 4H:1V or less 25% or less 150 feet 13 | P a g e 6H:1V or less 16.7% or less 200 feet 10H:1V or less 10% or less 250 feet Use Silt Fence Purpose Use of a silt fence reduces the transport of coarse sediment from a construction site by providing a temporary physical barrier to sediment and reducing the runoff velocities of overland flow. Conditions of Use 1. Silt fence may be used downslope of all disturbed areas. 2. Silt fence is not intended to treat concentrated flows, nor is it intended to treat substantial amounts of overland flow. Any concentrated flows must be conveyed through the drainage system to a sediment trap or pond. The only circumstance in which overland flow may be treated solely by a silt fence, rather than by a sediment trap or pond, is when the area draining to the fence is small (see "Criteria for Use as Primary Treatment" in Section D.2.1.3 above). Design and Installation Specifications 1. See Figure D.2.1.3.A and Figure D.2.1.3.B for details. 2.The geotextile used must meet the standards listed below. A copy of the manufacturer's fabric specifications must be available on site. 3. Standard strength fabric requires wire backing to increase the strength of the fence. Wire backing or closer post spacing may be required for extra strength fabric if field performance warrants a stronger fence. 4. Where the fence is installed, the slope shall be no steeper than 2H:1V. 5. If a typical silt fence (per Figure D.2.1.3.A) is used, the standard 4 x 4 trench may be reduced as long as the bottom 8 inches of the silt fence is well buried and secured in a trench that stabilizes the fence and does not allow water to bypass or undermine the silt fence. Maintenance Standards 1. Any damage shall be repaired immediately. 2. If concentrated flows are evident uphill of the fence, they must be intercepted and conveyed to a sediment trap or pond. 3. It is important to check the uphill side of the 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 or remove the trapped sediment. 4. Sediment must be removed when the sediment is 6 inches high. 14 | P a g e 5. If the filter fabric (geotextile) has deteriorated due to ultraviolet breakdown, it shall be replaced. 15 | P a g e 16 | P a g e 4. Traffic Area Stabilization Unsurfaced entrances, roads, and parking areas used by construction traffic shall be stabilized to minimize erosion and tracking of sediment off site. Stabilized construction entrances shall be installed as the first step in clearing and grading. At the County's discretion, road and parking area stabilization is not required during the dry season (unless dust is a concern) or if the site is underlain by coarse-grained soils. Roads and parking areas shall be stabilized immediately after initial grading. Purpose: The purpose of traffic area stabilization is to reduce the amount of sediment transported off site by construction vehicles and to reduce the erosion of areas disturbed by vehicle traffic. Sediment transported off site onto paved streets is a significant problem because it is difficult to effectively remove, and any sediment not removed ends up in the drainage system. Additionally, sediment on public right-of-way can pose a serious traffic hazard. Construction road and parking area stabilization is important because the combination of wet soil and heavy equipment traffic typically forms a slurry of easily erodible mud. Finally, stabilization also is an excellent form of dust control in the summer months. When to Install: The construction entrance is to be installed as the first step in clearing and grading. Construction road stabilization shall occur immediately after initial grading of the construction roads and parking areas. Measures to Use: There are two types of traffic area stabilization: (1) a stabilized construction entrance and (2) construction road/parking area stabilization. Both measures must be used as specified under "Conditions of Use" for each measure. Stabilize Construction Entrance Purpose Construction entrances are stabilized to reduce the amount of sediment transported onto paved roads by motor vehicles or runoff by constructing a stabilized pad of quarry spalls at entrances to construction sites. Conditions of Use Construction entrances shall be stabilized wherever traffic will be leaving a construction site and traveling on paved roads or other paved areas within 1,000 feet of the site. Access and exits shall be limited to one route if possible, or two for linear projects such as roadway where more than one access/exit is necessary for maneuvering large equipment. For residential construction provide stabilized construction entrances for each residence in addition to the main subdivision entrance. Stabilized surfaces shall be of sufficient length/width to provide vehicle access/parking, based on lot size/configuration. Design and Installation Specifications 1. See Figure D.2.1.4.A for details. 2. A separation geotextile shall be placed under the spalls to prevent fine sediment from pumping up into the rock pad. The geotextile shall meet the following standards: Grab Tensile Strength (ASTM D4632) 200 lbs min. Grab Tensile Elongation (ASTM D4632) 30% max.(woven) Puncture Strength (ASTM D6241) 495 lbs min. AOS (ASTM D4751) 20-45 (U.S. standard sieve size) 17 | P a g e 3. Do not use crushed concrete, cement, or calcium chloride for construction entrance stabilization because these products raise pH levels in stormwater and concrete discharge to surface waters of the State is prohibited. 4. Hog fuel (wood based mulch) may be substituted for or combined with quarry spalls in areas that will not be used for permanent roads. The effectiveness of hog fuel is highly variable, but it has been used successfully on many sites. It generally requires more maintenance than quarry spalls. Hog fuel is not recommended for entrance stabilization in urban areas. The inspector may at any time require the use of quarry spalls if the hog fuel is not preventing sediment from being tracked onto pavement or if the hog fuel is being carried onto pavement. Hog fuel is prohibited in permanent roadbeds because organics in the subgrade soils cause difficulties with compaction. 5. Fencing (see Section D.2.1.1) shall be installed as necessary to restrict traffic to the construction entrance. 6. Whenever possible, the entrance shall be constructed on a firm, compacted subgrade. This can substantially increase the effectiveness of the pad and reduce the need for maintenance. Maintenance Standards 1. Quarry spalls (or hog fuel) shall be added if the pad is no longer in accordance with the specifications. 2021 Surface Water Design Manual – Appendix D 7/23/2021 D-43 2. If the entrance 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 street sweeping, an increase in the dimensions of the entrance, or the installation of a wheel wash. If washing is used, it shall be done on an area covered with crushed rock, and wash water shall drain to a sediment trap or pond. 3. Any sediment that is tracked onto pavement shall be removed immediately by sweeping. The sediment collected by sweeping shall be removed or stabilized on site. The pavement shall not be cleaned by washing down the street, except when sweeping is ineffective and there is a threat to public safety. If it is necessary to wash the streets, a small sump must be constructed. The sediment would then be washed into the sump where it can be controlled. Wash water must be pumped back onto the site and cannot discharge to systems tributary to surface waters. 4. Any quarry spalls that are loosened from the pad and end up on the roadway shall be removed immediately. 5. If vehicles are entering or exiting the site at points other than the construction entrance(s), fencing (see Section D.2.1.1) shall be installed to control traffic. 18 | P a g e 19 | P a g e SWPPS MEASURES 1. 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 surface 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 projects include, but are not limited to, curbs, sidewalks, roads, bridges, foundations, floors, stormwater vaults, retaining walls, driveways and runways. Design and Installation Specifications 1. Assure that washout of concrete trucks, chutes, pumps, and internals is performed at an approved off-site location or in designated concrete washout areas. Do not wash out concrete trucks, chutes, pumps, or internals onto the ground, or into storm drains, open ditches, streets, or streams. Refer to BMP D.2.2.2 (p. D-78) for information on concrete washout areas. 2. Return unused concrete remaining in the truck and pump to the originating batch plant for recycling. Do not dump excess concrete on site, except in designated concrete washout areas. 3. Wash off hand tools including, but not limited to, screeds, shovels, rakes, floats, and trowels into formed areas awaiting future concrete pours only. 4. Do not wash out to formed areas awaiting infiltration BMPs. 5. Wash equipment difficult to move, such as concrete pavers in areas that do not directly drain to natural or constructed stormwater conveyances. 6. Do not allow washdown from areas, such as concrete aggregate driveways, to drain directly to natural or constructed stormwater conveyances. 7. Contain washwater and leftover product in a lined container when no formed areas are available,. Dispose of contained concrete in a manner that does not violate ground water or surface water quality standards. 8. Always use forms or solid barriers for concrete pours, such as pilings, within 15-feet of surface waters. 9. Refer to BMPs D.2.2.7 and D.2.2.8 for pH adjustment requirements. 10. Refer to the Construction Stormwater General Permit for pH monitoring requirements if the project involves one of the following activities: • Significant concrete work (greater than 1,000 cubic yards poured concrete or recycled concrete used over the life of a project). • The use of engineered soils amended with (but not limited to) Portland cement-treated base, cement kiln dust or fly ash. • Discharging stormwater to segments of water bodies on the 303(d) list (Category 5) for high pH. Maintenance Standards Check containers for holes in the liner daily during concrete pours and repair the same day. 2. MATERIAL DELIVERY, STORAGE AND CONTAINMENT Purpose Prevent, reduce, or eliminate the discharge of pollutants to the stormwater system or watercourses from material delivery and storage. Minimize the storage of hazardous materials on-site, store materials in a designated area, and install secondary containment. 20 | P a g e Conditions of Use These procedures are suitable for use at all construction sites with delivery and storage of the following materials: • Petroleum products such as fuel, oil and grease • Soil stabilizers and binders (e.g. Polyacrylamide) • Fertilizers, pesticides and herbicides • Detergents • Asphalt and concrete compounds • Hazardous chemicals such as acids, lime, adhesives, paints, solvents and curing compounds • Any other material that may be detrimental if released to the environment Design and Installation Specifications The following steps should be taken to minimize risk: 1. Temporary storage area should be located away from vehicular traffic, near the construction entrance(s), and away from waterways or storm drains. 2. Material Safety Data Sheets (MSDS) should be supplied for all materials stored. Chemicals should be kept in their original labeled containers. 3. Hazardous material storage on-site should be minimized. 4. Hazardous materials should be handled as infrequently as possible. 5. During the wet weather season (Oct 1 – April 30), consider storing materials in a covered area. 6. Materials should be stored in secondary containments, such as 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. 7. Do not store chemicals, drums, or bagged materials directly on the ground. Place these items on a pallet and, when possible, and within secondary containment. 8. If drums must be kept uncovered, store them at a slight angle to reduce ponding of rainwater on the lids to reduce corrosion. Domed plastic covers are inexpensive and snap to the top of drums, preventing water from collecting. Material Storage Areas and Secondary Containment Practices: 1. 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. 2. 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. 3. Secondary containment facilities shall be impervious to the materials stored therein for a minimum contact time of 72 hours. 4. 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. 5. Sufficient separation should be provided between stored containers to allow for spill cleanup and emergency response access. 6. During the wet weather season (Oct 1 – April 30), each secondary containment facility shall be covered during non-working days, prior to and during rain events. 7. Keep material storage areas clean, organized and equipped with an ample supply of appropriate spill clean-up material (spill kit). 21 | P a g e 8. The spill kit should include, at a minimum: • 1-Water Resistant Nylon Bag • 3-Oil Absorbent Socks 3”x 4’ • 2-Oil Absorbent Socks 3”x 10’ • 12-Oil Absorbent Pads 17”x19” • 1-Pair Splash Resistant Goggles • 3-Pair Nitrile Gloves • 10-Disposable Bags with Ties • Instructions 3. CONSTRUCTION STORMWATER CHEMICAL TREATMENT Purpose This BMP applies when using stormwater chemicals in batch treatment or flow-through treatment. Turbidity is difficult to control once fine particles are suspended in stormwater runoff from a construction site. Sedimentation ponds are effective at removing larger particulate matter by gravity settling, but are ineffective at removing smaller particulates such as clay and fine silt. Traditional erosion and sediment control BMPs may not be adequate to ensure compliance with the water quality standards for turbidity in receiving water. Chemical treatment can reliably provide exceptional reductions of turbidity and associated pollutants. Chemical treatment may be required to meet turbidity stormwater discharge requirements, especially when construction is to proceed through the wet season. Conditions of Use Formal written approval from Ecology is required for the use of chemical treatment regardless of site size. Accordingly, the requirements herein reflect Ecology’s review and approval process, including references to the Stormwater Management Manual for Western Washington (SMMWW). The Local Permitting Authority may also require review and approval. When approved, the chemical treatment systems must be included in the SWPPS portion of the project’s Construction Stormwater Pollution Prevention plan (CSWPP). Design and Installation Specifications (See Appendix II-B in the Stormwater Management Manual for Western Washington for background information on chemical treatment.) Criteria for Chemical Treatment Product Use: Chemically treated stormwater discharged from construction sites must be nontoxic to aquatic organisms. The Chemical Technology Assessment Protocol (CTAPE) must be used to evaluate chemicals proposed for stormwater treatment. Only chemicals approved by Ecology under the CTAPE may be used for stormwater treatment. The approved chemicals, their allowable application techniques (batch treatment or flow-through treatment), allowable application rates, and conditions of use can be found at the Department of Ecology Emerging Technologies website: http://www.ecy.wa.gov/programs/wq/stormwater/newtech/technologies.html . Treatment System Design Considerations: The design and operation of a chemical treatment system should take into consideration the factors that determine optimum, cost-effective performance. It is important to recognize the following: • Only Ecology approved chemicals may be used and must follow approved dose rate. • The pH of the stormwater must be in the proper range for the polymers to be effective, which is typically 6.5 to 8.5 • The coagulant must be mixed rapidly into the water to ensure proper dispersion. • A flocculation step is important to increase the rate of settling, to produce the lowest turbidity, and to keep the dosage rate as low as possible. • Too little energy input into the water during the flocculation phase results in flocs that are too small and/or insufficiently dense. Too much energy can rapidly destroy floc as it is formed. 22 | P a g e • Care must be taken in the design of the withdrawal system to minimize outflow velocities and to prevent floc discharge. Discharge from a batch treatment system should be directed through a physical filter such as a vegetated swale that would catch any unintended floc discharge. Currently, flow-through systems always discharge through the chemically enhanced sand filtration system. • System discharge rates must take into account downstream conveyance integrity. Polymer Batch Treatment Process Description: A batch chemical treatment system consists of the stormwater collection system (either temporary diversion or the permanent site drainage system), a storage pond, pumps, a chemical feed system, treatment cells, and interconnecting piping. The batch treatment system shall use a minimum of two lined treatment cells in addition to an untreated stormwater storage pond. Multiple treatment cells allow for clarification of treated water while other cells are being filled or emptied. Treatment cells may be ponds or tanks. Ponds with constructed earthen embankments greater than six feet high or which impound more than 10 acre-feet require special engineering analyses. The Ecology Dam Safety Section has specific design criteria for dams in Washington State (see http://www.ecy.wa.gov/programs/wr/dams/GuidanceDocs.html ). Stormwater is collected at interception point(s) on the site and is diverted by gravity or by pumping to an untreated stormwater storage pond or other untreated stormwater holding area. The stormwater is stored until treatment occurs. It is important that the holding pond be large enough to provide adequate storage. The first step in the treatment sequence is to check the pH of the stormwater in the untreated stormwater storage pond. The pH is adjusted by the application of carbon dioxide to mitigate high pH or a base to mitigate low pH until the stormwater in the storage pond is within the desired pH range, 6.5 to 8.5. When used, carbon dioxide is added immediately downstream of the transfer pump. Typically sodium bicarbonate (baking soda) is used as a base, although other bases may be used. When needed, base is added directly to the untreated stormwater storage pond. The stormwater is recirculated with the treatment pump to provide mixing in the storage pond. Initial pH adjustments should be based on daily bench tests. Further pH adjustments can be made at any point in the process. Once the stormwater is within the desired pH range (dependent on polymer being used), the stormwater is pumped from the untreated stormwater storage pond to a treatment cell as polymer is added. The polymer is added upstream of the pump to facilitate rapid mixing. After polymer addition, the water is kept in a lined treatment cell for clarification of the sediment-floc. In a batch mode process, clarification typically takes from 30 minutes to several hours. Prior to discharge samples are withdrawn for analysis of pH, flocculent chemical concentration, and turbidity. If both are acceptable, the treated water is discharged. Several configurations have been developed to withdraw treated water from the treatment cell. The original configuration is a device that withdraws the treated water from just beneath the water surface using a float with adjustable struts that prevent the float from settling on the cell bottom. This reduces the possibility of picking up sediment-floc from the bottom of the pond. The struts are usually set at a minimum clearance of about 12 inches; that is, the float will come within 12 inches of the bottom of the cell. Other systems have used vertical guides or cables which constrain the float, allowing it to drift up and down with the water level. More recent designs have an H-shaped array of pipes, set on the horizontal. This scheme provides for withdrawal from four points rather than one. This configuration reduces the likelihood of sucking settled solids from the bottom. It also reduces the tendency for a vortex to form. Inlet diffusers, a long floating or fixed pipe with many small holes in it, are also an option. Safety is a primary concern. Design should consider the hazards associated with operations, such as sampling. Facilities should be designed to reduce slip hazards and drowning. Tanks and ponds should have life rings, ladders, or steps extending from the bottom to the top. Polymer Flow-Through Treatment Process Description: At a minimum, a flow-through chemical treatment system consists of the stormwater collection system (either temporary diversion or the permanent site drainage system), an untreated stormwater storage pond, and the chemically enhanced sand filtration system. Stormwater is collected at interception point(s) on the site and is diverted by gravity or by pumping to an untreated stormwater storage pond or other untreated stormwater holding area. The stormwater is stored until treatment occurs. It is important that the holding pond be large enough to provide adequate storage. Stormwater is then pumped from the untreated stormwater storage pond to the chemically enhanced sand filtration system where polymer is added. Adjustments to pH may be necessary before chemical addition. The sand filtration system continually 23 | P a g e monitors the stormwater for turbidity and pH. If the discharge water is ever out of an acceptable range for turbidity or pH, the water is recycled to the untreated stormwater pond where it can be retreated. For batch treatment and flow-through treatment, the following equipment should be located in a lockable shed: • The chemical injector. • Secondary containment for acid, caustic, buffering compound, and treatment chemical. • Emergency shower and eyewash. • Monitoring equipment which consists of a pH meter and a turbidimeter. System Sizing: Certain sites are required to implement flow control for the developed sites. These sites must also control stormwater release rates during construction. Generally, these are sites that discharge stormwater directly, or indirectly, through a conveyance system, into a fresh water. System sizing is dependent on flow control requirements. Sizing Criteria for Batch Treatment Systems for Flow Control Exempt Water Bodies: The total volume of the untreated stormwater storage pond and treatment ponds or tanks must be large enough to treat stormwater that is produced during multiple day storm events. It is recommended that at a minimum the untreated stormwater storage pond be sized to hold 1.5 times the runoff volume of the 10-year, 24-hour storm event. Bypass should be provided around the chemical treatment system to accommodate extreme storm events. Runoff volume shall be calculated using the methods presented in Volume 3, Chapter 2 of the SWMMWW. Worst-case land cover conditions (i.e., producing the most runoff) should be used for analyses (in most cases, this would be the land cover conditions just prior to final landscaping). Primary settling should be encouraged in the untreated stormwater storage pond. A forebay with access for maintenance may be beneficial. There are two opposing considerations in sizing the treatment cells. A larger cell is able to treat a larger volume of water each time a batch is processed. However, the larger the cell the longer the time required to empty the cell. A larger cell may also be less effective at flocculation and therefore require a longer settling time. The simplest approach to sizing the treatment cell is to multiply the allowable discharge flow rate times the desired drawdown time. A 4-hour drawdown time allows one batch per cell per 8-hour work period, given 1 hour of flocculation followed by two hours of settling. If the discharge is directly to a flow control exempt receiving water listed in Appendix I-E of Volume I of the SWMMWW, or to an infiltration system, there is no discharge flow limit. Ponds sized for flow control water bodies must at a minimum meet the sizing criteria for flow control exempt waters. Sizing Criteria for Flow-Through Treatment Systems for Flow Control Exempt Water Bodies: When sizing storage ponds or tanks for flow-through systems for flow control exempt water bodies, the treatment system capacity should be a factor. The untreated stormwater storage pond or tank should be sized to hold 1.5 times the runoff volume of the 10-year, 24-hour storm event minus the treatment system flowrate for an 8-hour period. For a chitosan-enhanced sand filtration system, the treatment system flowrate should be sized using a hydraulic loading rate between 6-8 gpm/ft². Other hydraulic loading rates may be more appropriate for other systems. Bypass should be provided around the chemical treatment system to accommodate extreme storms. Runoff volume shall be calculated using the methods presented in Volume 3, Chapter 2 of the SWMMWW. Worst-case land cover conditions (i.e., producing the most runoff) should be used for analyses (in most cases, this would be the land cover conditions just prior to final landscaping). Sizing Criteria for Flow Control Water Bodies: Sites that must implement flow control for the developed site condition must also control stormwater release rates during construction. Construction site stormwater discharges shall not exceed the discharge durations of the pre-developed condition for the range of pre-developed discharge rates from ½ of the 2-year flow through the 10-year flow as predicted by an approved continuous runoff model. The pre-developed condition to be matched shall be the land cover condition immediately prior to the development project. This restriction on release rates can affect the size of the storage pond and treatment cells. The following is how WWHM can be used to determine the release rates from the chemical treatment systems: 1. Determine the pre-developed flow durations to be matched by entering the existing land use area under the “Pre-developed” scenario in WWHM. The default flow range is from ½ of the 2-year flow through the 10-year flow. 2. Enter the post developed land use area in the “Developed Unmitigated” scenario in WWHM. 3. Copy the land use information from the “Developed Unmitigated” to “Developed Mitigated” scenario. 4. While in the “Developed Mitigated” scenario, add a pond element under the basin element containing the post-developed land use areas. This pond element represents information on the available untreated stormwater storage and discharge from the chemical treatment system. In cases where the discharge from the chemical treatment system is controlled by a pump, a stage/storage/discharge (SSD) table representing the pond must be generated outside WWHM and imported into WWHM. 24 | P a g e WWHM can route the runoff from the post-developed condition through this SSD table (the pond) and determine compliance with the flow duration standard. This would be an iterative design procedure where if the initial SSD table proved to be inadequate, the designer would have to modify the SSD table outside WWHM and re-import in WWHM and route the runoff through it again. The iteration will continue until a pond that complies with the flow duration standard is correctly sized. Notes on SSD table characteristics: • The pump discharge rate would likely be initially set at just below ½ of the 2-year flow from the pre-developed condition. As runoff coming into the untreated stormwater storage pond increases and the available untreated stormwater storage volume gets used up, it would be necessary to increase the pump discharge rate above ½ of the 2-year. The increase(s) above ½ of the 2-year must be such that they provide some relief to the untreated stormwater storage needs but at the same time will not cause violations of the flow duration standard at the higher flows. The final design SSD table will identify the appropriate pumping rates and the corresponding stage and storages. • When building such a flow control system, the design must ensure that any automatic adjustments to the pumping rates will be as a result of changes to the available storage in accordance with the final design SSD table. 5. It should be noted that the above procedures would be used to meet the flow control requirements. The chemical treatment system must be able to meet the runoff treatment requirements. It is likely that the discharge flow rate of ½ of the 2-year or more may exceed the treatment capacity of the system. If that is the case, the untreated stormwater discharge rate(s) (i.e., influent to the treatment system) must be reduced to allow proper treatment. Any reduction in the flows would likely result in the need for a larger untreated stormwater storage volume. If the discharge is to a municipal storm drainage system, the allowable discharge rate may be limited by the capacity of the public system. It may be necessary to clean the municipal storm drainage system prior to the start of the discharge to prevent scouring solids from the drainage system. If the municipal storm drainage system discharges to a water body not on the flow control exempt list, the project site is subject to flow control requirements. Obtain permission from the owner of the collection system before discharging to it. If system design does not allow you to discharge at the slower rates as described above and if the site has a retention or detention pond that will serve the planned development, the discharge from the treatment system may be directed to the permanent retention/detention pond to comply with the flow control requirement. In this case, the untreated stormwater storage pond and treatment system will be sized according to the sizing criteria for flow-through treatment systems for flow control exempt water bodies described earlier except all discharge (water passing through the treatment system and stormwater bypassing the treatment system) will be directed into the permanent retention/detention pond. If site constraints make locating the untreated stormwater storage pond difficult, the permanent retention/detention pond may be divided to serve as the untreated stormwater storage pond and the post-treatment flow control pond. A berm or barrier must be used in this case so the untreated water does not mix with the treated water. Both untreated stormwater storage requirements, and adequate post-treatment flow control must be achieved. The post-treatment flow control pond’s revised dimensions must be entered into the WWHM and the WWHM must be run to confirm compliance with the flow control requirement. Maintenance Standards Monitoring: At a minimum, the following monitoring shall be conducted. Test results shall be recorded on a daily log kept on site. Additional testing may be required by the NPDES permit based on site conditions. Operational Monitoring: • Total volume treated and discharged. • Flow must be continuously monitored and recorded at not greater than 15-minute intervals. • Type and amount of chemical used for pH adjustment. • Amount of polymer used for treatment. • Settling time. Compliance Monitoring: Influent and effluent pH, flocculent chemical concentration, and turbidity must be continuously monitored and recorded at not greater than 15-minute intervals. pH and turbidity of the receiving water. Biomonitoring: 25 | P a g e Treated stormwater must be non-toxic to aquatic organisms. Treated stormwater must be tested for aquatic toxicity or residual chemicals. Frequency of biomonitoring will be determined by Ecology. Residual chemical tests must be approved by Ecology prior to their use. If testing treated stormwater for aquatic toxicity, you must test for acute (lethal) toxicity. Bioassays shall be conducted by a laboratory accredited by Ecology, unless otherwise approved by Ecology. Acute toxicity tests shall be conducted per the CTAPE protocol. Discharge Compliance: Prior to discharge, treated stormwater must be sampled and tested for compliance with pH, flocculent chemical concentration, and turbidity limits. These limits may be established by the Construction Stormwater General Permit or a site- specific discharge permit. Sampling and testing for other pollutants may also be necessary at some sites. pH must be within the range of 6.5 to 8.5 standard units and not cause a change in the pH of the receiving water of more than 0.2 standard units. Treated stormwater samples and measurements shall be taken from the discharge pipe or another location representative of the nature of the treated stormwater discharge. Samples used for determining compliance with the water quality standards in the receiving water shall not be taken from the treatment pond prior to decanting. Compliance with the water quality standards is determined in the receiving water. Operator Training: Each contractor who intends to use chemical treatment shall be trained by an experienced contractor. Each site using chemical treatment must have an operator trained and certified by an organization approved by Ecology. Standard BMPs: Surface stabilization BMPs should be implemented on site to prevent significant erosion. All sites shall use a truck wheel wash to prevent tracking of sediment off site. Sediment Removal and Disposal: • Sediment shall be removed from the storage or treatment cells as necessary. Typically, sediment removal is required at least once during a wet season and at the decommissioning of the cells. Sediment remaining in the cells between batches may enhance the settling process and reduce the required chemical dosage. • Sediment that is known to be non-toxic may be incorporated into the site away from drainages. 4. CONSTRUCTION STORMWATER FILTRATION Purpose Filtration removes sediment from runoff originating from disturbed areas of the site. Background Information: Filtration with sand media has been used for over a century to treat water and wastewater. The use of sand filtration for treatment of stormwater has developed recently, generally to treat runoff from streets, parking lots, and residential areas. The application of filtration to construction stormwater treatment is currently under development. Conditions of Use Traditional BMPs used to control soil erosion and sediment loss from sites under development may not be adequate to ensure compliance with the water quality standard for turbidity in the receiving water. Filtration may be used in conjunction with gravity settling to remove sediment as small as fine silt (0.5 μm). The reduction in turbidity will be dependent on the particle size distribution of the sediment in the stormwater. In some circumstances, sedimentation and filtration may achieve compliance with the water quality standard for turbidity. The use of construction stormwater filtration does not require approval from Ecology as long as treatment chemicals are not used. Filtration in conjunction with polymer treatment requires testing under the Chemical Technology Assessment Protocol – Ecology (CTAPE) before it can be initiated. Approval from the appropriate regional Ecology office must be obtained at each site where polymers use is proposed prior to use. For more guidance on stormwater chemical treatment see BMP D.2.2.5. Design and Installation Specifications Two types of filtration systems may be applied to construction stormwater treatment: rapid and slow. Rapid sand filters are the typical system used for water and wastewater treatment. They can achieve relatively high hydraulic flow rates, on the order of 2 to 20 gpm/sf, because they have automatic backwash systems to remove accumulated solids. In contrast, slow sand filters have very low hydraulic rates, on the order of 0.02 gpm/sf, because they do not have backwash systems. Slow sand filtration has generally been used to treat stormwater. Slow sand filtration is mechanically simple in comparison to rapid sand filtration but requires a much larger filter area. Filtration Equipment. 26 | P a g e Sand media filters are available with automatic backwashing features that can filter to 50 μm particle size. Screen or bag filters can filter down to 5 μm. Fiber wound filters can remove particles down to 0.5 μm. Filters should be sequenced from the largest to the smallest pore opening. Sediment removal efficiency will be related to particle size distribution in the stormwater. Treatment Process Description. Stormwater is collected at interception point(s) on the site and is diverted to an untreated stormwater sediment pond or tank for removal of large sediment and storage of the stormwater before it is treated by the filtration system. The untreated stormwater is pumped from the trap, pond, or tank through the filtration system in a rapid sand filtration system. Slow sand filtration systems are designed as flow through systems using gravity. Maintenance Standards Rapid sand filters typically have automatic backwash systems that are triggered by a pre-set pressure drop across the filter. If the backwash water volume is not large or substantially more turbid than the untreated stormwater stored in the holding pond or tank, backwash return to the untreated stormwater pond or tank may be appropriate. However, other means of treatment and disposal may be necessary. • Screen, bag, and fiber filters must be cleaned and/or replaced when they become clogged. • Sediment shall be removed from the storage and/or treatment ponds as necessary. Typically, sediment removal is required once or twice during a wet season and at the decommissioning of the ponds. Sizing Criteria for Flow-Through Treatment Systems for Flow Control Exempt Water Bodies: When sizing storage ponds or tanks for flow-through systems for flow control exempt water bodies the treatment system capacity should be a factor. The untreated stormwater storage pond or tank should be sized to hold 1.5 times the runoff volume of the 10-year, 24-hour storm event minus the treatment system flowrate for an 8-hour period. For a chitosan-enhanced sand filtration system, the treatment system flowrate should be sized using a hydraulic loading rate between 6-8 gpm/ft². Other hydraulic loading rates may be more appropriate for other systems. Bypass should be provided around the chemical treatment system to accommodate extreme storms. Runoff volume shall be calculated using the methods presented in Volume 3, Chapter 2 of the SWMMWW (or Chapter 4 of the King County Surface Water Design Manual if no chemicals are proposed for use). Worst-case conditions (i.e., producing the most runoff) should be used for analyses (most likely conditions present prior to final landscaping). Sizing Criteria for Flow Control Water Bodies: Sites that must implement flow control for the developed site condition must also control stormwater release rates during construction. Construction site stormwater discharges shall not exceed the discharge durations of the pre-developed condition for the range of pre-developed discharge rates from 1/2 of the 2-year flow through the 10-year flow as predicted by an approved continuous runoff model. The pre-developed condition to be matched shall be the land cover condition immediately prior to the development project. This restriction on release rates can affect the size of the storage pond, the filtration system, and the flow rate through the filter system. The following is how WWHM can be used to determine the release rates from the filtration systems: 1. Determine the pre-developed flow durations to be matched by entering the land use area under the “Pre-developed” scenario in WWHM. The default flow range is from ½ of the 2-year flow through the 10-year flow. 2. Enter the post developed land use area in the “Developed Unmitigated” scenario in WWHM. 3. Copy the land use information from the “Developed Unmitigated” to “Developed Mitigated” scenario. 4. There are two possible ways to model stormwater filtration systems: a. The stormwater filtration system uses an untreated stormwater storage pond/tank and the discharge from this pond/tank is pumped to one or more filters. In-line filtration chemicals would be added to the flow right after the pond/tank and before the filter(s). Because the discharge is pumped, WWHM can’t generate a stage/storage /discharge (SSD) table for this system. This system is modeled the same way as described Ecology’s BMP C250 (or BMP D.2.2.5 when seeking King County approval for non-chemical treatment) and is as follows: While in the “Developed Mitigated” scenario, add a pond element under the basin element containing the post-developed land use areas. This pond element represents information on the available untreated stormwater storage and discharge from the filtration system. In cases where the discharge from the filtration system is controlled by a pump, a stage/storage/discharge (SSD) table representing the pond must be generated outside WWHM and imported into WWHM. WWHM can route the runoff from the post-developed condition through this SSD table (the pond) and determine compliance with the flow duration standard. 27 | P a g e This would be an iterative design procedure where if the initial SSD table proved to be out of compliance, the designer would have to modify the SSD table outside WWHM and re-import in WWHM and route the runoff through it again. The iteration will continue until a pond that enables compliance with the flow duration standard is designed. Notes on SSD table characteristics: • The pump discharge rate would likely be initially set at just below ½ if the 2-year flow from the pre-developed condition. As runoff coming into the untreated stormwater storage pond increases and the available untreated stormwater storage volume gets used up, it would be necessary to increase the pump discharge rate above ½ of the 2-year. The increase(s) above ½ of the 2-year must be such that they provide some relief to the untreated stormwater storage needs but at the same time they will not cause violations of the flow duration standard at the higher flows. The final design SSD table will identify the appropriate pumping rates and the corresponding stage and storages. • When building such a flow control system, the design must ensure that any automatic adjustments to the pumping rates will be as a result of changes to the available storage in accordance with the final design SSD table. b. The stormwater filtration system uses a storage pond/tank and the discharge from this pond/tank gravity flows to the filter. This is usually a slow sand filter system and it is possible to model it in WWHM as a Filter element or as a combination of Pond and Filter element placed in series. The stage/storage/discharge table(s) may then be generated within WWHM as follows: i. While in the “Developed Mitigated” scenario, add a Filter element under the basin element containing the post-developed land use areas. The length and width of this filter element would have to be the same as the bottom length and width of the upstream untreated stormwater storage pond/tank. ii. In cases where the length and width of the filter is not the same as those for the bottom of the upstream untreated stormwater storage tank/pond, the treatment system may be modeled as a Pond element followed by a Filter element. By having these two elements, WWHM would then generate a SSD table for the storage pond which then gravity flows to the Filter element. The Filter element downstream of the untreated stormwater storage pond would have a storage component through the media, and an overflow component for when the filtration capacity is exceeded. WWHM can route the runoff from the post-developed condition through the treatment systems in 4b and determine compliance with the flow duration standard. This would be an iterative design procedure where if the initial sizing estimates for the treatment system proved to be inadequate, the designer would have to modify the system and route the runoff through it again. The iteration would continue until compliance with the flow duration standard is achieved. 5. It should be noted that the above procedures would be used to meet the flow control requirements. The filtration system must be able to meet the runoff treatment requirements. It is likely that the discharge flow rate of ½ of the 2-year or more may exceed the treatment capacity of the system. If that is the case, the untreated stormwater discharge rate(s) (i.e., influent to the treatment system) must be reduced to allow proper treatment. Any reduction in the flows would likely result in the need for a larger untreated stormwater storage volume. If system design does not allow you to discharge at the slower rates as described above and if the site has a retention or detention pond that will serve the planned development, the discharge from the treatment system may be directed to the permanent retention/detention pond to comply with the flow control requirements. In this case, the untreated stormwater storage pond and treatment system will be sized according to the sizing criteria for flow-through treatment systems for flow control exempt waterbodies described earlier except all discharges (water passing through the treatment system and stormwater bypassing the treatment system) will be directed into the permanent retention/detention pond. If site constraints make locating the untreated stormwater storage pond difficult, the permanent retention/detention pond may be divided to serve as the untreated stormwater discharge pond and the post-treatment flow control pond. A berm or barrier must be used in this case so the untreated water does not mix with the treated water. Both untreated stormwater storage requirements, and adequate post- treatment flow control must be achieved. The post-treatment flow control pond’s revised dimensions must be entered into the WWHM and the WWHM must be run to confirm compliance with the flow control requirement. 5. HIGH pH NEUTRALIZATION USING CO2 Purpose When pH levels in stormwater rise above 8.5 it is necessary to lower the pH levels to the acceptable range of 6.5 to 8.5, this process is called pH neutralization. pH neutralization involves the use of solid or compressed carbon dioxide gas in water requiring neutralization. Neutralized stormwater may be discharged to surface waters under the General Construction NPDES permit. 28 | P a g e Neutralized process water such as concrete truck wash-out, hydro-demolition, or saw-cutting slurry must be managed to prevent discharge to surface waters. Any stormwater contaminated during concrete work is considered process wastewater and must not be discharged to surface waters. Reason for pH Neutralization: A pH level range of 6.5 to 8.5 is typical for most natural watercourses, and this neutral pH is required for the survival of aquatic organisms. Should the pH rise or drop out of this range, fish and other aquatic organisms may become stressed and may die. Calcium hardness can contribute to high pH values and cause toxicity that is associated with high pH conditions. A high level of calcium hardness in waters of the state is not allowed. The water quality standard for pH in Washington State is in the range of 6.5 to 8.5. Ground water standard for calcium and other dissolved solids in Washington State is less than 500 mg/l. Conditions of Use Causes of High pH: High pH at construction sites is most commonly caused by the contact of stormwater with poured or recycled concrete, cement, mortars, and other Portland cement or lime containing construction materials. (See BMP D.2.2.1, Concrete Handling for more information on concrete handling procedures). The principal caustic agent in cement is calcium hydroxide (free lime). Advantages of CO2 Sparging: • Rapidly neutralizes high pH water. • Cost effective and safer to handle than acid compounds. • CO2 is self-buffering. It is difficult to overdose and create harmfully low pH levels. • Material is readily available. The Chemical Process: When carbon dioxide (CO2) is added to water (H2O), carbonic acid (H2CO3) is formed which can further dissociate into a proton (H+) and a bicarbonate anion (HCO3-) as shown below: CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3- The free proton is a weak acid that can lower the pH. Water temperature has an effect on the reaction as well. The colder the water temperature is the slower the reaction occurs and the warmer the water temperature is the quicker the reaction occurs. Most construction applications in Washington State have water temperatures in the 50°F or higher range so the reaction is almost simultaneous. Design and Installation Specifications Treatment Process: High pH water may be treated using continuous treatment, continuous discharge systems. These manufactured systems continuously monitor influent and effluent pH to ensure that pH values are within an acceptable range before being discharged. All systems must have fail safe automatic shut off switches in the event that pH is not within the acceptable discharge range. Only trained operators may operate manufactured systems. System manufacturers often provide trained operators or training on their devices. The following procedure may be used when not using a continuous discharge system: 1. Prior to treatment, the appropriate jurisdiction should be notified in accordance with the regulations set by the jurisdiction. 2. Every effort should be made to isolate the potential high pH water in order to treat it separately from other stormwater on- site. 3. Water should be stored in an acceptable storage facility, detention pond, or containment cell prior to treatment. 4. Transfer water to be treated to the treatment structure. Ensure that treatment structure size is sufficient to hold the amount of water that is to be treated. Do not fill tank completely, allow at least 2 feet of freeboard. 5. The operator samples the water for pH and notes the clarity of the water. As a rule of thumb, less CO2 is necessary for clearer water. This information should be recorded. 6. In the pH adjustment structure, add CO2 until the pH falls in the range of 6.9-7.1. Remember that pH water quality standards apply so adjusting pH to within 0.2 pH units of receiving water (background pH) is recommended. It is unlikely that pH can be adjusted to within 0.2 pH units using dry ice. Compressed carbon dioxide gas should be introduced to the water using a carbon dioxide diffuser located near the bottom of the tank, this will allow carbon dioxide to bubble up through the water and diffuse more evenly. 29 | P a g e 7. Slowly discharge the water making sure water does not get stirred up in the process. Release about 80% of the water from the structure leaving any sludge behind. 8. Discharge treated water through a pond or drainage system. 9. Excess sludge needs to be disposed of properly as concrete waste. If several batches of water are undergoing pH treatment, sludge can be left in treatment structure for the next batch treatment. Dispose of sludge when it fills 50% of tank volume. Sites that must implement flow control for the developed site must also control stormwater release rates during construction. All treated stormwater must go through a flow control facility before being released to surface waters which require flow control. Maintenance Standards Safety and Materials Handling: • All equipment should be handled in accordance with OSHA rules and regulations. • Follow manufacturer guidelines for materials handling. Operator Records: Each operator should provide: • A diagram of the monitoring and treatment equipment. • A description of the pumping rates and capacity the treatment equipment is capable of treating. Each operator should keep a written record of the following: • Client name and phone number. • Date of treatment. • Weather conditions. • Project name and location. • Volume of water treated. • pH of untreated water. • Amount of CO2 needed to adjust water to a pH range of 6.9-7.1. • pH of treated water. • Discharge point location and description. A copy of this record should be given to the client/contractor who should retain the record for three years. 6. pH CONTROL FOR HIGH pH WATER Purpose When pH levels in stormwater rise above 8.5 it is necessary to lower the pH levels to the acceptable range of 6.5 to 8.5, this process is called pH neutralization. Stormwater with pH levels exceeding water quality standards may be treated by infiltration, dispersion in vegetation or compost, pumping to a sanitary sewer, disposal at a permitted concrete batch plant with pH neutralization capabilities, or carbon dioxide sparging. BMP D.2.2.7, High pH Neutralization Using CO2 gives guidelines for carbon dioxide sparging. Reason for pH Neutralization: A pH level range of 6.5 to 8.5 is typical for most natural watercourses, and this pH range is required for the survival of aquatic organisms. Should the pH rise or drop out of this range, fish and other aquatic organisms may become stressed and may die. Conditions of Use Causes of High pH: High pH levels at construction sites are most commonly caused by the contact of stormwater with poured or recycled concrete, cement, mortars, and other Portland cement or lime containing construction materials. (See BMP D.2.2.1, Concrete Handling for more information on concrete handling procedures). The principal caustic agent in cement is calcium hydroxide (free lime). 30 | P a g e Design and Installation Specifications Disposal Methods: Infiltration • Infiltration is only allowed if soil type allows all water to infiltrate (no surface runoff) without causing or contributing to a violation of surface or ground water quality standards. • Infiltration techniques should be consistent with Chapter 5 of the King County Surface Water Design Manual Dispersion • Dispersion techniques should be consistent with Chapter 5 and Appendix C of the King County Surface Water Design Manual Sanitary Sewer Disposal • Local sewer authority approval is required prior to disposal via the sanitary sewer. Concrete Batch Plant Disposal • Only permitted facilities may accept high pH water. • Facility should be contacted before treatment to ensure they can accept the high pH water. Stormwater Discharge Any pH treatment options that generate treated water that must be discharged off site are subject to flow control requirements. Sites that must implement flow control for the developed site must also control stormwater release rates during construction. All treated stormwater must go through a flow control facility before being released to surface waters which require flow control. 7. USE OF HIGH pH SOIL AMENDMENTS ON CONSTRUCTION SITES The use of soil amendments (including cement treated base (CTB) and cement kiln dust (CKD)) on development sites must be approved by King County. The approval process is described in "Processing Requirements for Use of Soil Amendments on Construction Sites" below. Use of Soil Amendments It is sometimes a construction practice to add soil amendments to the surfaces of some construction areas in order to stabilize the ground for building. This practice includes placing an additive on the ground then mixing with the soil to a specified depth and finally compacting the mix. When mixed with the soil, the moisture in the ground may allow these additives to create a chemical reaction that cures similar to concrete and may absorb excessive moisture to allow soils to be compacted. The end result is a stable site for constructing a road or building pad. Because soil amendments may be rich in lime content and other material, water runoff from these areas can be affected. If not controlled and treated, this could result in a degradation of water quality and natural drainage systems. Because these additives come in a fine powder form, the actual application can create fugitive dust. When mixed with water, some additives can become corrosive. Definitions The following are definitions of soil amendment products that are allowed for use under these procedures: 1. Cement Kiln Dust (CKD) is a by-product in the manufacturing of cement9. 2. Cement Treated Base (CTB) utilizes Portland Cement Type II as the soil additive. CTB/CKD Soil Amendment BMPs Table D.2.2.9.A on the following pages lists twelve BMP categories of action and specific BMPs for each category to be applied when proposing CTB/CKD soil amendments or using soil amendments onsite. Note: Additional BMPs may be required to prevent adverse impacts to the public and/or the environment. It is the responsibility of the permit holder to remain in compliance with all other applicable local, state, and federal regulations. 31 | P a g e 32 | P a g e 33 | P a g e 34 | P a g e 35 | P a g e 36 | P a g e Processing Requirements for Use of High pH Soil Amendments on Construction Sites10 Purpose This section establishes procedures for implementing BMPs when using high pH soil amendments on construction sites. See Table D.2.2.9.A for a description of the BMPs. This section outlines an expedited review process and typical approval conditions that will allow contractors and builders to use soil amendments without impacting water quality. Additional BMPs may be required based upon site specific conditions that may warrant more protection. This policy is limited to those amendments, defined below, commonly known to add stability to sloppy soil conditions but which can alter water runoff quality. Authority: KCC 9.12.025 prohibits discharges of polluted or contaminated water into surface or storm water drainage systems. The purpose of this statute is to protect surface and ground water by regulating the discharge of potentially contaminated surface water. If soil amendments are proposed with an initial application, an environmental review is required, under SEPA, which assesses impacts, provides public input and mitigated conditions for its use. King County Road Design and Construction Standards, Sections 4.04 and 4.05 also require an engineered design for use of a soil amendment on road surfaces or around drainage systems. The design may incorporate a thorough assessment of soil composition and laboratory analysis. The Surface Water Design Manual authorizes DLS-Permitting to adopt BMPs for the control and protection of surface water. Currently, for all sites, the BMPs established in this policy are the minimum standards that shall be applied. Procedure An applicant may apply for use of soil amendments allowed under this policy anytime during the permit application review or after the permit has been issued and site construction is underway. After making a submittal to DLS-Permitting, the applicant 37 | P a g e may receive approval conditions. Conditions may vary from site to site, but typically will include many of the BMPs included in this policy. Applicants should identify any use of soil amendments as early in the process as possible to avoid delays in obtaining approval for use during the construction phase. If a site has known soil and water conditions that might make work during rainy periods difficult, they may want to plan to use soil amendments on their site. Obviously, if this issue is addressed at the permit review phase, implementation in the field can occur without delay. However, because of the potential risks of surface water pollution discharge and required treatment, an environmental assessment will be necessary before conditions for use can be established. Limitations This policy applies to the intended use of soil amendments in areas that will be covered by impervious surfaces. For areas not covered by impervious surfaces, additional reviews, study, and BMPs may be required. In addition, alterations to original approved use plans will require a resubmittal for approval. Approval for the use of the soil amendments in unincorporated King County can only occur by strictly following the procedures contained herein and not by any other approval obtained from DLS- Permitting. Submittal Requirements To obtain approval for the use of soil amendments allowed under this policy, the applicant shall prepare a submittal package to DLS-Permitting that includes the following: • Letter to DLS-Permitting requesting use of soil amendments at a construction site allowed under this policy. • Document or letter attachment that identifies source of materials and description of mixing and laydown process, plan for disposal of treated contact water, sanitary sewer permits and/or BMPs, and special precautions proposed to prevent the contamination of surface or stormwater drainage systems, other than 'sealed' drainage systems. • Site Plan: Show a site plan map which: 1) Shows overall grading plan showing existing and proposed contours. 2) Identifies sensitive areas and permanent or temporary drainage facilities. 3) Identifies areas that soil amendment is planned. 4) Shows depths of application and percent of amendment to be used. 5) Shows location of special wheel wash facility. 6) Shows location of collection and conveyance swales or pipes for contact water. 7) Shows location of sealed storage/treatment tanks or temporary ponds (fully lined). 8) Identifies any discharge point from the site into natural drainage systems. 9) Includes soil log locations that identify seasonal high groundwater areas. Report and analysis of engineering mix design which includes depths of application and percent of amendment usage. For proposals that use CKD and CKD additive, provide analysis of source material for soluble contaminants. Include a description of fuel source. Monitoring criteria, including locations for pH and turbidity testing. Provide contingency plan should use of soil amendment and site and weather conditions result in polluted or contact water entering natural drainage systems. Provide contact information or water quality specialist assigned to monitor application of soil amendments and BMPs. If the project is under construction, the applicant shall contact the DLS-Permitting inspector assigned to the project to initiate a review for compliance with the BMPs and requirements herein. Otherwise contact the planner or engineer assigned to review the permit or land use application. Review and Approval Once the review has been completed, the applicant shall be notified by letter which stipulates the conditions of approval. Prior to authorizing the use of soil amendments at the site, the applicant shall provide a special restoration financial guarantee cash deposit in the amount as determined by the existing, established processes. Note: It remains the applicant/contractor’s responsibility to comply with any other applicable state or federal regulations such as use of NIOSH respiratory protection, safety goggles, gloves and protective clothing whenever using hazardous materials. 38 | P a g e Applicable Standards Typically, all proposals using soil amendments in unincorporated King County shall have these conditions as standard requirements: 1. Prior to any application of CKD/CTB, the general contract shall hold a preconstruction meeting with the assigned DLS- Permitting inspector at least 3 working days in advance. 2. CKD will not be permitted for use in areas adjacent to or in proximity to wetlands and streams areas. CTB may or may not be permitted in these areas. 3. Areas not covered by impervious surfaces: • CKD will not be permitted in areas that will not be covered by impervious surfaces. • If CTB is proposed in these areas, an analysis of whether or not the soil amendment will change the post-development runoff characteristics and the permanent stormwater facilities were sized appropriately shall be submitted for review. Use of CTB in areas not permanently covered by impervious surface may require re-sizing of the permanent stormwater facilities. 4. If CKD is proposed, the contractor shall provide mill certificates verifying the product composition. The contractor/developer must be prepared to follow BMPs during and after soil treatment and be prepared to treat runoff from the treatment area(s) immediately. All stormwater collection systems must be in place and all equipment (pH meters, dry ice, etc.) must be onsite. 5. Collection of stormwater (see BMP #5 in Table D.2.2.9.A): • Stormwater from the application area shall be kept separate from and prevented from comingling with uncontaminated stormwater. • During the application of CKD/CTB, stormwater runoff shall be collected in temporary collection systems and shall not be allowed to enter the permanent facilities. Permanent drainage systems shall be capped to prevent contact stormwater from entering the inlets of the catch basins. Stormwater from the application area shall not be collected in the temporary/permanent detention ponds, even if the underlying soils are 'impermeable'. 6. Treatment: If necessary, pH adjustment shall be done in the collection tanks or temporary ponds and not in the permanent detention ponds. 7. Disposal options: The proposal to use CKD/CTB must contain a disposal plan that may include one or a combination of sanitary sewer or approved offsite disposal. Treated contact water may be discharged to the sanitary sewer if authorizations are obtained from the King County Industrial Waste Program (206-477-5300) and the local sewer district. All discharge conditions (e.g. pH, settleable solids) must be followed. If a sanitary sewer is not available at the site, contact water may be transported offsite to an approved site for disposal and proof of proper disposal must be submitted to King County. All authorizations for disposal shall be obtained prior to CKD/CTB application. • Infiltration: Depending on the site conditions, pH-adjusted stormwater may be infiltrated. Prior to infiltration, pH must be between 6.5 and 8.5. • Surface Water: Contact water from the application area shall not be discharged to surface waters, even if treatment has adjusted the pH. 8. Emergency backup plan: An emergency backup plan must be prepared and ready to implement to handle large quantities of stormwater. 9. Monitoring shall be conducted to determine that contact stormwater is not leaving the site. Offsite monitoring shall also be conducted to identify impacts to adjacent water bodies. Bonding may be required to cover mitigation of impacts and restoration. 10. A soils specialist will establish the mixing percentage for onsite soils. Soil amendments will never occur in excess of the ability of the onsite equipment and resources to meet all BMP requirements. 11. For sites one acre or larger, a National Pollutant Discharge Elimination System (NPDES) Construction Stormwater permit must be obtained from Ecology. NPDES permits and 'Stormwater Pollution Prevention Plans (SWPPPs) must be amended and the use of CKD/CTB must be approved by Ecology prior to application. The contractor/developer shall comply will all federal, state, and local regulations. A health and safety plan may be required for the protection of King County inspectors. Additional BMPs may be applicable depending on mix design, proximity of wetlands or streams (e.g. within 300 feet of class/type I and 100 feet or less for other types) and site conditions. 39 | P a g e 8. MAINTAIN PROTECTIVE BMPS Pollutant protection measures shall be maintained to assure continued performance of their intended function. Reporting and documentation shall be kept current and made available to DLS-Permitting as indicated. Purpose: The purpose of maintaining protective BMPs is to provide effective pollutant protection when and where required by the plan and the project, and to provide timely and relevant project information. When to Maintain: Protection measures shall be monitored per Section D.2.4.4 at a minimum, continuously during operation, and promptly maintained to fully functioning condition as necessary to assure continued performance of their intended function. Documentation shall be kept current per specific BMP requirements. Measures to Use: 1. Maintain and repair all pollutant control BMPs as needed to assure continued performance of their intended function in accordance with BMP specifications. 2. Maintain and repair storage locations for equipment and materials associated with BMP processes. Conduct materials disposal in compliance with County regulatory requirements. 3. As required, provide current reporting and performance documentation at an accessible location for the site inspector and other DLS-Permitting staff. 4. Remove all temporary pollutant control BMPs prior to final construction approval, or within 30 days after achieving final site stabilization or after the temporary BMPs are no longer needed. 9. MANAGE THE PROJECT SWPPP requirements shall be implemented and managed as part of the overall CSWPP plan. Concrete construction and its impacts are primary among pollutant concerns on site development projects. Fueling operations and materials containment of treatment chemicals and other project materials are also typical pollutant concerns. Operations that produce these and other pollutants are often conducted by subcontractors and their laborers, yet may require specific protective measures, documentation and reporting. Protective measures and BMPs need to be made available prior to construction and suitable oversight provided to assure inspection, monitoring and documentation requirements are met. Projects shall assign a qualified CSWPP Supervisor (Section D.2.3.1) to be the primary contact for SWPPP and ESC issues and reporting, coordination with subcontractors and implementation of the CSWPP plan as a whole. Measures to Use: 1. Phase development projects to the maximum degree practicable and take into account seasonal work limits. 2. Inspection and monitoring – Inspect, maintain, and repair all BMPs as needed to assure continued performance of their intended function. Conduct site inspections and monitoring in accordance with the Construction Stormwater General Permit and King County requirements. Coordinate with subcontractors and laborers to assure the SWPPP measures are followed. 3. Documentation and reporting: – Inspect, maintain, and repair all BMPs as needed to assure continued performance of their intended function. Document site inspections and monitoring in accordance with the Construction Stormwater General Permit, specific BMP conditions and King County requirements. Log sheets provided in Reference Section 8 may be used if appropriate. Follow reporting requirements and provide documentation as requested to DLS-Permitting staff. 4. Maintaining an updated construction SWPPP – Maintain, update, and implement the SWPPP in accordance with the Construction Stormwater General Permit and King County requirements. Obtain approval for specific SWPPP measures (e.g., chemical treatments of stormwater) well in advance of need. Coordinate SWPPP plan updates with the site inspector (see Section D.2.4.1). 40 | P a g e Core Requirements #6: MAINTENANCE AND OPERATIONS The following are the Maintenance Instructions that will be used for the selected BMPs: Maintenance and operation of all drainage facilities is the responsibility of the applicant or property owner, except those facilities for which King County assumes maintenance and operation as described below and in KCC 9.04.115 and KCC 9.04.120. Drainage facilities must be maintained and operated in accordance with the maintenance standards in Appendix A of 2021 Surface Water Design Manual. MAINTENANCE INSTRUCTIONS FOR BASIC DISPERSION Your property contains a stormwater management flow control BMP (best management practice) called "basic dispersion," which was installed to mitigate the stormwater quantity and quality impacts of some or all of the impervious surfaces or non- native pervious surfaces on your property. Basic dispersion is a strategy for utilizing any available capacity of onsite vegetated areas to retain, absorb, and filter the runoff from developed surfaces. This flow control BMP has two primary components that must be maintained: (1) the devices that disperse runoff from the developed surfaces and (2) the vegetated area over which runoff is dispersed. Dispersion Devices The dispersion devices used on your property include the following as indicated on the flow control BMP site plan: -Splash blocks, -Sheet flow. The size, placement, composition, and downstream flowpaths of these devices as depicted by the flow control BMP site plan and design details must be maintained and may not be changed without written approval either from the King County Water and Land Resources Division or through a future development permit from King County. Dispersion devices must be inspected annually and after major storm events to identify and repair any physical defects. When native soil is exposed or erosion channels are present, the sources of the erosion or concentrated flow need to be identified and mitigated. Concentrated flow can be mitigated by leveling the edge of the pervious area and/or realigning or replenishing the rocks in the dispersion device, such as in rock pads and gravel filled trenches. Vegetated Flowpaths The vegetated area over which runoff is dispersed must be maintained in good condition free of bare spots and obstructions that would concentrate flows. 41 | P a g e 42 | P a g e 43 | P a g e 44 | P a g e Core Requirements #7: FINANCIAL GUARANTEES AND LIABILITIES Not applicable. CORE REQUIREMENT #8: WATER QUALITY FACILITIES Not applicable. The proposed project is exempt from Water Quality Requirements. EXEMPTIONS FROM CORE REQUIREMENT #8 There are four possible exemptions from the requirement to provide a water quality facility per Core Requirement #8: 1. Surface Area Exemption A proposed project or any threshold discharge area within the site of a project is exempt if it meets all of the following criteria: a) Less than 5,000 square feet of new plus replaced PGIS will be created, AND b) Less than ¾ acre of new PGPS will be added. 45 | P a g e The Proposed Driveway area = 4,620 SF to be added to the project. CORE REQUIREMENT #9: FLOW CONTROL BMPS Dispersion BMPs will be used manage stormwater runoff from the proposed driveways. 8. SPECIAL REQUIREMENTS COMPLIANCE SPECIAL REQUIREMENT #1: OTHER ADOPTED AREA-SPECIFIC REQUIREMENTS • Critical Drainage Areas (CDAs): No runoff is anticipated from the proposed project to be discharged to any critical area or any area has drainage flooding/problems history or any likelihood to harm the welfare and safety of the surrounding community. • Master Drainage Plans (MDPs): Not applicable for the proposed project, because the following criteria are not met: -The project is designated for an Urban Planned Development (UPD) on the King County Comprehensive Plan Land Use Map, OR -The project would, at full buildout, result in 50 acres or more of new impervious surface within a single -subbasin or multiple subbasins that are hydraulically connected10 across subbasin boundaries, OR -The project site is 50 acres or more • Basin Plans (BPs): Not Applicable to the Proposed Project. • Salmon Conservation Plans (SCPs): Not Applicable to the Proposed Project. • Stormwater Compliance Plans (SWCPs): The proposed project runoff is not draining to the City/County Municipal Stormwater Catch Basins. Also, given the fact that the proposed project is a Single Family House with proposed Driveway less than 5,000sf, there is no concerns on the discharged water quality. • Lake Management Plans (LMPs): No runoff is anticipated from the project site to drain into the following lakes: Lake Alice Lake Allen 46 | P a g e Angle Lake Beaver Lake • Flood Hazard Management Plan (FHMPs): Not applicable to the proposed project. No flood zones located on the project downstream. • Shared Facility Drainage Plans (SFDPs): No applicable to the proposed project. As explained earlier in this report, this project is exempted from the use of drainage facilities. SPECIAL REQUIREMENT #2: FLOOD HAZARD AREA DELINEATION No applicable because the proposed project does not contain nor adjacent to a flood hazard area. Check the attached City of Renton COR MAP, the closes critical area to the project site downstream is a wetland and a stream located on the adjacent property on the North side of the subject property. Also, the No drainage complain area in the downstream of the proposed project drainage point. SPECIAL REQUIREMENT #3: FLOOD PROTECTION FACILITIES No applicable because the proposed project does not rely on an existing flood protection facility for protection against hazards posed by erosion or inundation. SPECIAL REQUIREMENT #4: SOURCE CONTROLS No applicable because the proposed project is for religious use building with new PGIS (Driveways) less than 5,000 sf and does require a commercial building nor commercial site development. SPECIAL REQUIREMENT #5: OIL CONTROL No applicable because the proposed project is Single Family House with PGIS (Driveways) less than 5,000 sf and the following criteria were not met: - Develops a site that will have high-use site characteristics, OR - is a redevelopment project proposing $100,000 or more of improvements to an existing high- use site, OR - is a redevelopment project that results in new plus replaced pollution generating impervious surfaces of 5,000 square feet or more or new pollution generating pervious surface of ¾ acre or more improvements to an existing high-use site … APPENDIX A SITE PLAN PROPERTY LINE = 165.97' PROPERTY LINE = 165.97' BSBL = 20.0' PR O P E R T Y L I N E = 2 3 0 . 0 ' BS B L = 5 . 0 ' PR O P E R T Y L I N E = 2 3 0 . 0 ' BS B L = 5 . 0 ' BSBL = 20.0' AREA OF WORK SE 176TH ST LANDSCAPE EXIST LIVING QUARTERS (REFER TO OTHER PERMITTED STRUCT.) U. D E C K L. D E C K 45'-10"89'-3"20'-0 " 45'- 1 1 " 148'- 5 " 472 4 7 0 466 470 464 46 0 45 8 45 6 4 5 4 4 5 2 45 0 44 8 44 6 44 4 4 4 2 46 8 4 6 6 46 4 462 46 0 458 456 454 45 2 x x x x x x x x x x x x x x x x x x x x S D S D SD OH P OH P OH P OH P OH P OH PBIKE RACK (5-11 BICYCLES) 30' - 11". 10' LANDSCAPE BUFFER 46 8 5'-0" 18'-0"9'-0 " 2 1 8 7 6 9 10 5 4 3 46 2 ELEC. VEHICLE CHARGING STATION WD FENCED TRASH ENCLOSURE 72'- 0 " (8) S T A N D A R D S T A L L S @ 9 ' - 0 " E A . 9'-0"33'-6 1/2"+/- LOW RETAINING WALL GARDEN AREA 100' - 0 " VE G E T A T I O N F L O W P A T H 100'- 0 " VE G E T A T I O N F L O W P A T H 2' WIDE 20' LON G D I S P E R S I O N TRENCH - BMP SHEET FLOW DISPERSION - BMP SL O P E I S 1 0 % SL O P E I S 1 0 % N IMPERVIOUS AREA CALC.: LOT SIZE = 38,134 SF LANDSCAPE = 10,921 SF PAVED SURFACE = 23,098 SF DECKS/RAMP = 1,361 SF STRUCT FTPRNT = 2,858 SF TOT. IMPERV. = 27,317 SF % OF IMPERV. = 72% VICINITY MAP BO D E T E M P L E CO M M E R C I A L I N T E R . RE N O V A T I O N & R O O F R E P . 11 4 1 0 S E P E T R O V I T S K Y R D RE N T O N , W A 9 8 0 5 5 SI T E P L A N 1"=30'-00" U.N.O 12/22/2025DATE: PR O J E C T : SCALE: DWG. NO.: SK Y G A T E E N G I N E E R S A N D CO N S U L T A N T S L L C , KE R E L L O S Y O U S S E F , P . E . 21 6 1 9 3 6 T H D R S E - B O T H E L L W A , 9 8 0 2 1 PH O N E : ( 4 2 5 ) 6 2 3 - 4 6 1 9 KE R E L L O S . Y @ S K Y G A T E N G I N E E R I N G . C O M SHEET C-1 CI V I L S T A N D A R D D E T A I L NOT TO SCALE 09/25/2024DATE: PR O J E C T : SCALE: DWG. NO.: SK Y G A T E E N G I N E E R S A N D CO N S U L T A N T S L L C , KE R E L L O S Y O U S S E F , P . E . 21 6 1 9 3 6 T H D R S E - B O T H E L L W A , 9 8 0 2 1 PH O N E : ( 4 2 5 ) 6 2 3 - 4 6 1 9 KE R E L L O S . Y @ S K Y G A T E N G I N E E R I N G . C O M SHEET C-3 BO D E T E M P L E CO M M E R C I A L I N T E R . RE N O V A T I O N & R O O F R E P . 11 4 1 0 S E P E T R O V I T S K Y R D RE N T O N , W A 9 8 0 5 5 APPENDIX B WWHM 2012MODEL WWHM2012 PROJECT REPORT default[7]12/19/2025 11:50:03 PM Page 2 General Model Information WWHM2012 Project Name:default[7] Site Name:BO DE TEMPLE RENOVATION AND ROOF REPLACEMENT PROJECT Site Address:11410 SE Petrovitsky Rd City:Renton Report Date:12/19/2025 Gage:Seatac Data Start:1948/10/01 Data End:2009/09/30 Timestep:15 Minute Precip Scale:1.000 Version Date:2023/03/31 Version:4.2.19 POC Thresholds Low Flow Threshold for POC1:50 Percent of the 2 Year High Flow Threshold for POC1:50 Year default[7]12/19/2025 11:50:03 PM Page 3 Landuse Basin Data Predeveloped Land Use Predeveloped Bypass:No GroundWater:No Pervious Land Use acre A B, Lawn, Flat 0.60952 Pervious Total 0.60952 Impervious Land Use acre ROOF TOPS FLAT 0.080808 DRIVEWAYS FLAT 0.185 Impervious Total 0.265808 Basin Total 0.875328 default[7]12/19/2025 11:50:03 PM Page 4 Mitigated Land Use Mitigated Bypass:No GroundWater:No Pervious Land Use acre A B, Lawn, Flat 0.503466 Pervious Total 0.503466 Impervious Land Use acre ROOF TOPS FLAT 0.080808 DRIVEWAYS FLAT 0.29123 Impervious Total 0.372038 Basin Total 0.875504 default[7]12/19/2025 11:50:03 PM Page 5 Routing Elements Predeveloped Routing default[7]12/19/2025 11:50:03 PM Page 6 Mitigated Routing default[7]12/19/2025 11:50:03 PM Page 7 Analysis Results POC 1 + Predeveloped x Mitigated Predeveloped Landuse Totals for POC #1 Total Pervious Area:0.60952 Total Impervious Area:0.265808 Mitigated Landuse Totals for POC #1 Total Pervious Area:0.503466 Total Impervious Area:0.372038 Flow Frequency Method:Log Pearson Type III 17B Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.104888 5 year 0.141035 10 year 0.168426 25 year 0.207192 50 year 0.239253 100 year 0.274186 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 0.144487 5 year 0.188725 10 year 0.220846 25 year 0.264767 50 year 0.299989 100 year 0.337429 Annual Peaks Annual Peaks for Predeveloped and Mitigated. POC #1 Year Predeveloped Mitigated 1949 0.134 0.186 1950 0.163 0.199 1951 0.100 0.130 1952 0.073 0.102 1953 0.079 0.110 1954 0.089 0.121 1955 0.093 0.131 1956 0.092 0.129 1957 0.104 0.146 1958 0.084 0.118 default[7]12/19/2025 11:50:26 PM Page 8 1959 0.086 0.120 1960 0.089 0.119 1961 0.089 0.125 1962 0.078 0.109 1963 0.090 0.124 1964 0.085 0.118 1965 0.112 0.154 1966 0.072 0.101 1967 0.154 0.190 1968 0.141 0.197 1969 0.098 0.137 1970 0.095 0.132 1971 0.113 0.158 1972 0.155 0.195 1973 0.070 0.099 1974 0.103 0.144 1975 0.118 0.166 1976 0.081 0.113 1977 0.086 0.121 1978 0.105 0.148 1979 0.144 0.202 1980 0.130 0.181 1981 0.106 0.148 1982 0.149 0.209 1983 0.122 0.170 1984 0.077 0.108 1985 0.106 0.148 1986 0.092 0.128 1987 0.141 0.198 1988 0.086 0.120 1989 0.107 0.150 1990 0.303 0.354 1991 0.176 0.229 1992 0.076 0.106 1993 0.066 0.092 1994 0.072 0.100 1995 0.094 0.131 1996 0.141 0.167 1997 0.112 0.148 1998 0.098 0.138 1999 0.201 0.282 2000 0.101 0.141 2001 0.110 0.154 2002 0.128 0.180 2003 0.103 0.143 2004 0.188 0.264 2005 0.086 0.121 2006 0.090 0.118 2007 0.307 0.345 2008 0.175 0.222 2009 0.131 0.183 Ranked Annual Peaks Ranked Annual Peaks for Predeveloped and Mitigated. POC #1 Rank Predeveloped Mitigated 1 0.3066 0.3543 2 0.3035 0.3447 3 0.2013 0.2818 default[7]12/19/2025 11:50:26 PM Page 9 4 0.1885 0.2637 5 0.1765 0.2285 6 0.1755 0.2225 7 0.1628 0.2091 8 0.1549 0.2020 9 0.1544 0.1985 10 0.1494 0.1978 11 0.1443 0.1971 12 0.1413 0.1947 13 0.1409 0.1904 14 0.1408 0.1861 15 0.1341 0.1833 16 0.1310 0.1813 17 0.1296 0.1797 18 0.1284 0.1701 19 0.1216 0.1674 20 0.1183 0.1656 21 0.1126 0.1576 22 0.1121 0.1543 23 0.1117 0.1541 24 0.1101 0.1501 25 0.1072 0.1482 26 0.1059 0.1479 27 0.1057 0.1479 28 0.1054 0.1476 29 0.1045 0.1461 30 0.1034 0.1438 31 0.1027 0.1427 32 0.1010 0.1409 33 0.1001 0.1377 34 0.0984 0.1370 35 0.0979 0.1322 36 0.0945 0.1315 37 0.0939 0.1308 38 0.0935 0.1297 39 0.0921 0.1288 40 0.0916 0.1282 41 0.0897 0.1248 42 0.0897 0.1235 43 0.0892 0.1209 44 0.0892 0.1208 45 0.0890 0.1206 46 0.0865 0.1204 47 0.0862 0.1202 48 0.0862 0.1188 49 0.0859 0.1184 50 0.0848 0.1178 51 0.0842 0.1177 52 0.0809 0.1125 53 0.0788 0.1102 54 0.0776 0.1087 55 0.0772 0.1077 56 0.0759 0.1063 57 0.0734 0.1025 58 0.0724 0.1010 59 0.0719 0.1005 60 0.0704 0.0985 61 0.0658 0.0920 default[7]12/19/2025 11:50:26 PM Page 10 default[7]12/19/2025 11:50:26 PM Page 11 Duration Flows The Duration Matching Failed Flow(cfs)Predev Mit Percentage Pass/Fail 0.0524 1663 4806 288 Fail 0.0543 1465 4316 294 Fail 0.0562 1293 3884 300 Fail 0.0581 1137 3499 307 Fail 0.0600 1018 3208 315 Fail 0.0619 916 2922 318 Fail 0.0638 819 2629 321 Fail 0.0657 740 2419 326 Fail 0.0675 660 2207 334 Fail 0.0694 601 2005 333 Fail 0.0713 545 1809 331 Fail 0.0732 491 1647 335 Fail 0.0751 446 1502 336 Fail 0.0770 414 1374 331 Fail 0.0789 384 1248 325 Fail 0.0807 366 1144 312 Fail 0.0826 332 1040 313 Fail 0.0845 305 962 315 Fail 0.0864 278 897 322 Fail 0.0883 253 834 329 Fail 0.0902 232 767 330 Fail 0.0921 212 706 333 Fail 0.0940 189 651 344 Fail 0.0958 173 610 352 Fail 0.0977 166 566 340 Fail 0.0996 149 528 354 Fail 0.1015 138 487 352 Fail 0.1034 131 454 346 Fail 0.1053 121 433 357 Fail 0.1072 111 409 368 Fail 0.1091 106 392 369 Fail 0.1109 100 358 358 Fail 0.1128 92 339 368 Fail 0.1147 87 315 362 Fail 0.1166 85 299 351 Fail 0.1185 78 282 361 Fail 0.1204 75 263 350 Fail 0.1223 71 240 338 Fail 0.1241 67 227 338 Fail 0.1260 65 211 324 Fail 0.1279 60 198 330 Fail 0.1298 51 190 372 Fail 0.1317 48 172 358 Fail 0.1336 46 164 356 Fail 0.1355 41 157 382 Fail 0.1374 38 145 381 Fail 0.1392 37 137 370 Fail 0.1411 33 132 400 Fail 0.1430 30 127 423 Fail 0.1449 27 121 448 Fail 0.1468 26 118 453 Fail 0.1487 25 105 419 Fail 0.1506 22 100 454 Fail 0.1525 22 98 445 Fail default[7]12/19/2025 11:50:26 PM Page 12 0.1543 21 92 438 Fail 0.1562 19 88 463 Fail 0.1581 18 83 461 Fail 0.1600 18 80 444 Fail 0.1619 16 80 500 Fail 0.1638 15 75 500 Fail 0.1657 15 69 460 Fail 0.1675 15 64 426 Fail 0.1694 14 63 450 Fail 0.1713 14 62 442 Fail 0.1732 14 60 428 Fail 0.1751 14 57 407 Fail 0.1770 11 54 490 Fail 0.1789 10 51 510 Fail 0.1808 9 47 522 Fail 0.1826 9 44 488 Fail 0.1845 8 41 512 Fail 0.1864 8 36 450 Fail 0.1883 8 35 437 Fail 0.1902 7 33 471 Fail 0.1921 7 30 428 Fail 0.1940 7 29 414 Fail 0.1959 7 25 357 Fail 0.1977 6 23 383 Fail 0.1996 5 20 400 Fail 0.2015 4 18 450 Fail 0.2034 4 17 425 Fail 0.2053 4 17 425 Fail 0.2072 4 17 425 Fail 0.2091 4 17 425 Fail 0.2109 4 16 400 Fail 0.2128 3 15 500 Fail 0.2147 3 15 500 Fail 0.2166 3 15 500 Fail 0.2185 3 15 500 Fail 0.2204 3 15 500 Fail 0.2223 3 15 500 Fail 0.2242 3 14 466 Fail 0.2260 3 14 466 Fail 0.2279 3 14 466 Fail 0.2298 3 13 433 Fail 0.2317 3 12 400 Fail 0.2336 3 11 366 Fail 0.2355 3 10 333 Fail 0.2374 3 10 333 Fail 0.2393 3 10 333 Fail The development has an increase in flow durations from 1/2 Predeveloped 2 year flow to the 2 year flow or more than a 10% increase from the 2 year to the 50 year flow. The development has an increase in flow durations for more than 50% of the flows for the range of the duration analysis. default[7]12/19/2025 11:50:26 PM Page 13 Water Quality Water Quality BMP Flow and Volume for POC #1 On-line facility volume:0 acre-feet On-line facility target flow:0 cfs. Adjusted for 15 min:0 cfs. Off-line facility target flow:0 cfs. Adjusted for 15 min:0 cfs. default[7]12/19/2025 11:50:26 PM Page 14 LID Report default[7]12/19/2025 11:50:33 PM Page 15 Model Default Modifications Total of 0 changes have been made. PERLND Changes No PERLND changes have been made. IMPLND Changes No IMPLND changes have been made. default[7]12/19/2025 11:50:33 PM Page 16 Appendix Predeveloped Schematic default[7]12/19/2025 11:50:33 PM Page 17 Mitigated Schematic default[7]12/19/2025 11:50:34 PM Page 18 Predeveloped UCI File RUN GLOBAL WWHM4 model simulation START 1948 10 01 END 2009 09 30 RUN INTERP OUTPUT LEVEL 3 0 RESUME 0 RUN 1 UNIT SYSTEM 1 END GLOBAL FILES <File> <Un#> <-----------File Name------------------------------>*** <-ID-> *** WDM 26 default[7].wdm MESSU 25 Predefault[7].MES 27 Predefault[7].L61 28 Predefault[7].L62 30 POCdefault[7]1.dat END FILES OPN SEQUENCE INGRP INDELT 00:15 PERLND 7 IMPLND 4 IMPLND 5 COPY 501 DISPLY 1 END INGRP END OPN SEQUENCE DISPLY DISPLY-INFO1 # - #<----------Title----------->***TRAN PIVL DIG1 FIL1 PYR DIG2 FIL2 YRND 1 Predeveloped MAX 1 2 30 9 END DISPLY-INFO1 END DISPLY COPY TIMESERIES # - # NPT NMN *** 1 1 1 501 1 1 END TIMESERIES END COPY GENER OPCODE # # OPCD *** END OPCODE PARM # # K *** END PARM END GENER PERLND GEN-INFO <PLS ><-------Name------->NBLKS Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** 7 A/B, Lawn, Flat 1 1 1 1 27 0 END GEN-INFO *** Section PWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC *** 7 0 0 1 0 0 0 0 0 0 0 0 0 END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ***************************** PIVL PYR # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ********* 7 0 0 4 0 0 0 0 0 0 0 0 0 1 9 default[7]12/19/2025 11:50:34 PM Page 19 END PRINT-INFO PWAT-PARM1 <PLS > PWATER variable monthly parameter value flags *** # - # CSNO RTOP UZFG VCS VUZ VNN VIFW VIRC VLE INFC HWT *** 7 0 0 0 0 0 0 0 0 0 0 0 END PWAT-PARM1 PWAT-PARM2 <PLS > PWATER input info: Part 2 *** # - # ***FOREST LZSN INFILT LSUR SLSUR KVARY AGWRC 7 0 5 0.8 400 0.05 0.3 0.996 END PWAT-PARM2 PWAT-PARM3 <PLS > PWATER input info: Part 3 *** # - # ***PETMAX PETMIN INFEXP INFILD DEEPFR BASETP AGWETP 7 0 0 2 2 0 0 0 END PWAT-PARM3 PWAT-PARM4 <PLS > PWATER input info: Part 4 *** # - # CEPSC UZSN NSUR INTFW IRC LZETP *** 7 0.1 0.5 0.25 0 0.7 0.25 END PWAT-PARM4 PWAT-STATE1 <PLS > *** Initial conditions at start of simulation ran from 1990 to end of 1992 (pat 1-11-95) RUN 21 *** # - # *** CEPS SURS UZS IFWS LZS AGWS GWVS 7 0 0 0 0 3 1 0 END PWAT-STATE1 END PERLND IMPLND GEN-INFO <PLS ><-------Name-------> Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** 4 ROOF TOPS/FLAT 1 1 1 27 0 5 DRIVEWAYS/FLAT 1 1 1 27 0 END GEN-INFO *** Section IWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW IWAT SLD IWG IQAL *** 4 0 0 1 0 0 0 5 0 0 1 0 0 0 END ACTIVITY PRINT-INFO <ILS > ******** Print-flags ******** PIVL PYR # - # ATMP SNOW IWAT SLD IWG IQAL ********* 4 0 0 4 0 0 4 1 9 5 0 0 4 0 0 0 1 9 END PRINT-INFO IWAT-PARM1 <PLS > IWATER variable monthly parameter value flags *** # - # CSNO RTOP VRS VNN RTLI *** 4 0 0 0 0 0 5 0 0 0 0 0 END IWAT-PARM1 IWAT-PARM2 <PLS > IWATER input info: Part 2 *** # - # *** LSUR SLSUR NSUR RETSC 4 400 0.01 0.1 0.1 5 400 0.01 0.1 0.1 default[7]12/19/2025 11:50:34 PM Page 20 END IWAT-PARM2 IWAT-PARM3 <PLS > IWATER input info: Part 3 *** # - # ***PETMAX PETMIN 4 0 0 5 0 0 END IWAT-PARM3 IWAT-STATE1 <PLS > *** Initial conditions at start of simulation # - # *** RETS SURS 4 0 0 5 0 0 END IWAT-STATE1 END IMPLND SCHEMATIC <-Source-> <--Area--> <-Target-> MBLK *** <Name> # <-factor-> <Name> # Tbl# *** Predeveloped*** PERLND 7 0.60952 COPY 501 12 PERLND 7 0.60952 COPY 501 13 IMPLND 4 0.080808 COPY 501 15 IMPLND 5 0.185 COPY 501 15 ******Routing****** END SCHEMATIC NETWORK <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** COPY 501 OUTPUT MEAN 1 1 48.4 DISPLY 1 INPUT TIMSER 1 <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** END NETWORK RCHRES GEN-INFO RCHRES Name Nexits Unit Systems Printer *** # - #<------------------><---> User T-series Engl Metr LKFG *** in out *** END GEN-INFO *** Section RCHRES*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # HYFG ADFG CNFG HTFG SDFG GQFG OXFG NUFG PKFG PHFG *** END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ******************* PIVL PYR # - # HYDR ADCA CONS HEAT SED GQL OXRX NUTR PLNK PHCB PIVL PYR ********* END PRINT-INFO HYDR-PARM1 RCHRES Flags for each HYDR Section *** # - # VC A1 A2 A3 ODFVFG for each *** ODGTFG for each FUNCT for each FG FG FG FG possible exit *** possible exit possible exit * * * * * * * * * * * * * * *** END HYDR-PARM1 HYDR-PARM2 # - # FTABNO LEN DELTH STCOR KS DB50 *** <------><--------><--------><--------><--------><--------><--------> *** END HYDR-PARM2 APPENDIX-CTESCPLAN default[7]12/19/2025 11:50:34 PM Page 21 HYDR-INIT RCHRES Initial conditions for each HYDR section *** # - # *** VOL Initial value of COLIND Initial value of OUTDGT *** ac-ft for each possible exit for each possible exit <------><--------> <---><---><---><---><---> *** <---><---><---><---><---> END HYDR-INIT END RCHRES SPEC-ACTIONS END SPEC-ACTIONS FTABLES END FTABLES EXT SOURCES <-Volume-> <Member> SsysSgap<--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # tem strg<-factor->strg <Name> # # <Name> # # *** WDM 2 PREC ENGL 1 PERLND 1 999 EXTNL PREC WDM 2 PREC ENGL 1 IMPLND 1 999 EXTNL PREC WDM 1 EVAP ENGL 0.76 PERLND 1 999 EXTNL PETINP WDM 1 EVAP ENGL 0.76 IMPLND 1 999 EXTNL PETINP END EXT SOURCES EXT TARGETS <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Volume-> <Member> Tsys Tgap Amd *** <Name> # <Name> # #<-factor->strg <Name> # <Name> tem strg strg*** COPY 501 OUTPUT MEAN 1 1 48.4 WDM 501 FLOW ENGL REPL END EXT TARGETS MASS-LINK <Volume> <-Grp> <-Member-><--Mult--> <Target> <-Grp> <-Member->*** <Name> <Name> # #<-factor-> <Name> <Name> # #*** MASS-LINK 12 PERLND PWATER SURO 0.083333 COPY INPUT MEAN END MASS-LINK 12 MASS-LINK 13 PERLND PWATER IFWO 0.083333 COPY INPUT MEAN END MASS-LINK 13 MASS-LINK 15 IMPLND IWATER SURO 0.083333 COPY INPUT MEAN END MASS-LINK 15 END MASS-LINK END RUN default[7]12/19/2025 11:50:34 PM Page 22 Mitigated UCI File RUN GLOBAL WWHM4 model simulation START 1948 10 01 END 2009 09 30 RUN INTERP OUTPUT LEVEL 3 0 RESUME 0 RUN 1 UNIT SYSTEM 1 END GLOBAL FILES <File> <Un#> <-----------File Name------------------------------>*** <-ID-> *** WDM 26 default[7].wdm MESSU 25 Mitdefault[7].MES 27 Mitdefault[7].L61 28 Mitdefault[7].L62 30 POCdefault[7]1.dat END FILES OPN SEQUENCE INGRP INDELT 00:15 PERLND 7 IMPLND 4 IMPLND 5 COPY 501 DISPLY 1 END INGRP END OPN SEQUENCE DISPLY DISPLY-INFO1 # - #<----------Title----------->***TRAN PIVL DIG1 FIL1 PYR DIG2 FIL2 YRND 1 Mitigated MAX 1 2 30 9 END DISPLY-INFO1 END DISPLY COPY TIMESERIES # - # NPT NMN *** 1 1 1 501 1 1 END TIMESERIES END COPY GENER OPCODE # # OPCD *** END OPCODE PARM # # K *** END PARM END GENER PERLND GEN-INFO <PLS ><-------Name------->NBLKS Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** 7 A/B, Lawn, Flat 1 1 1 1 27 0 END GEN-INFO *** Section PWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC *** 7 0 0 1 0 0 0 0 0 0 0 0 0 END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ***************************** PIVL PYR # - # ATMP SNOW PWAT SED PST PWG PQAL MSTL PEST NITR PHOS TRAC ********* 7 0 0 4 0 0 0 0 0 0 0 0 0 1 9 default[7]12/19/2025 11:50:34 PM Page 23 END PRINT-INFO PWAT-PARM1 <PLS > PWATER variable monthly parameter value flags *** # - # CSNO RTOP UZFG VCS VUZ VNN VIFW VIRC VLE INFC HWT *** 7 0 0 0 0 0 0 0 0 0 0 0 END PWAT-PARM1 PWAT-PARM2 <PLS > PWATER input info: Part 2 *** # - # ***FOREST LZSN INFILT LSUR SLSUR KVARY AGWRC 7 0 5 0.8 400 0.05 0.3 0.996 END PWAT-PARM2 PWAT-PARM3 <PLS > PWATER input info: Part 3 *** # - # ***PETMAX PETMIN INFEXP INFILD DEEPFR BASETP AGWETP 7 0 0 2 2 0 0 0 END PWAT-PARM3 PWAT-PARM4 <PLS > PWATER input info: Part 4 *** # - # CEPSC UZSN NSUR INTFW IRC LZETP *** 7 0.1 0.5 0.25 0 0.7 0.25 END PWAT-PARM4 PWAT-STATE1 <PLS > *** Initial conditions at start of simulation ran from 1990 to end of 1992 (pat 1-11-95) RUN 21 *** # - # *** CEPS SURS UZS IFWS LZS AGWS GWVS 7 0 0 0 0 3 1 0 END PWAT-STATE1 END PERLND IMPLND GEN-INFO <PLS ><-------Name-------> Unit-systems Printer *** # - # User t-series Engl Metr *** in out *** 4 ROOF TOPS/FLAT 1 1 1 27 0 5 DRIVEWAYS/FLAT 1 1 1 27 0 END GEN-INFO *** Section IWATER*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # ATMP SNOW IWAT SLD IWG IQAL *** 4 0 0 1 0 0 0 5 0 0 1 0 0 0 END ACTIVITY PRINT-INFO <ILS > ******** Print-flags ******** PIVL PYR # - # ATMP SNOW IWAT SLD IWG IQAL ********* 4 0 0 4 0 0 4 1 9 5 0 0 4 0 0 0 1 9 END PRINT-INFO IWAT-PARM1 <PLS > IWATER variable monthly parameter value flags *** # - # CSNO RTOP VRS VNN RTLI *** 4 0 0 0 0 0 5 0 0 0 0 0 END IWAT-PARM1 IWAT-PARM2 <PLS > IWATER input info: Part 2 *** # - # *** LSUR SLSUR NSUR RETSC 4 400 0.01 0.1 0.1 5 400 0.01 0.1 0.1 default[7]12/19/2025 11:50:34 PM Page 24 END IWAT-PARM2 IWAT-PARM3 <PLS > IWATER input info: Part 3 *** # - # ***PETMAX PETMIN 4 0 0 5 0 0 END IWAT-PARM3 IWAT-STATE1 <PLS > *** Initial conditions at start of simulation # - # *** RETS SURS 4 0 0 5 0 0 END IWAT-STATE1 END IMPLND SCHEMATIC <-Source-> <--Area--> <-Target-> MBLK *** <Name> # <-factor-> <Name> # Tbl# *** Mitigated*** PERLND 7 0.503466 COPY 501 12 PERLND 7 0.503466 COPY 501 13 IMPLND 4 0.080808 COPY 501 15 IMPLND 5 0.29123 COPY 501 15 ******Routing****** END SCHEMATIC NETWORK <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** COPY 501 OUTPUT MEAN 1 1 48.4 DISPLY 1 INPUT TIMSER 1 <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # #<-factor->strg <Name> # # <Name> # # *** END NETWORK RCHRES GEN-INFO RCHRES Name Nexits Unit Systems Printer *** # - #<------------------><---> User T-series Engl Metr LKFG *** in out *** END GEN-INFO *** Section RCHRES*** ACTIVITY <PLS > ************* Active Sections ***************************** # - # HYFG ADFG CNFG HTFG SDFG GQFG OXFG NUFG PKFG PHFG *** END ACTIVITY PRINT-INFO <PLS > ***************** Print-flags ******************* PIVL PYR # - # HYDR ADCA CONS HEAT SED GQL OXRX NUTR PLNK PHCB PIVL PYR ********* END PRINT-INFO HYDR-PARM1 RCHRES Flags for each HYDR Section *** # - # VC A1 A2 A3 ODFVFG for each *** ODGTFG for each FUNCT for each FG FG FG FG possible exit *** possible exit possible exit * * * * * * * * * * * * * * *** END HYDR-PARM1 HYDR-PARM2 # - # FTABNO LEN DELTH STCOR KS DB50 *** <------><--------><--------><--------><--------><--------><--------> *** END HYDR-PARM2 default[7]12/19/2025 11:50:34 PM Page 25 HYDR-INIT RCHRES Initial conditions for each HYDR section *** # - # *** VOL Initial value of COLIND Initial value of OUTDGT *** ac-ft for each possible exit for each possible exit <------><--------> <---><---><---><---><---> *** <---><---><---><---><---> END HYDR-INIT END RCHRES SPEC-ACTIONS END SPEC-ACTIONS FTABLES END FTABLES EXT SOURCES <-Volume-> <Member> SsysSgap<--Mult-->Tran <-Target vols> <-Grp> <-Member-> *** <Name> # <Name> # tem strg<-factor->strg <Name> # # <Name> # # *** WDM 2 PREC ENGL 1 PERLND 1 999 EXTNL PREC WDM 2 PREC ENGL 1 IMPLND 1 999 EXTNL PREC WDM 1 EVAP ENGL 0.76 PERLND 1 999 EXTNL PETINP WDM 1 EVAP ENGL 0.76 IMPLND 1 999 EXTNL PETINP END EXT SOURCES EXT TARGETS <-Volume-> <-Grp> <-Member-><--Mult-->Tran <-Volume-> <Member> Tsys Tgap Amd *** <Name> # <Name> # #<-factor->strg <Name> # <Name> tem strg strg*** COPY 1 OUTPUT MEAN 1 1 48.4 WDM 701 FLOW ENGL REPL COPY 501 OUTPUT MEAN 1 1 48.4 WDM 801 FLOW ENGL REPL END EXT TARGETS MASS-LINK <Volume> <-Grp> <-Member-><--Mult--> <Target> <-Grp> <-Member->*** <Name> <Name> # #<-factor-> <Name> <Name> # #*** MASS-LINK 12 PERLND PWATER SURO 0.083333 COPY INPUT MEAN END MASS-LINK 12 MASS-LINK 13 PERLND PWATER IFWO 0.083333 COPY INPUT MEAN END MASS-LINK 13 MASS-LINK 15 IMPLND IWATER SURO 0.083333 COPY INPUT MEAN END MASS-LINK 15 END MASS-LINK END RUN default[7]12/19/2025 11:50:34 PM Page 26 Predeveloped HSPF Message File default[7]12/19/2025 11:50:34 PM Page 27 Mitigated HSPF Message File default[7]12/19/2025 11:50:34 PM Page 28 Disclaimer Legal Notice This program and accompanying documentation are provided 'as-is' without warranty of any kind. The entire risk regarding the performance and results of this program is assumed by End User. Clear Creek Solutions Inc. and the governmental licensee or sublicensees disclaim all warranties, either expressed or implied, including but not limited to implied warranties of program and accompanying documentation. In no event shall Clear Creek Solutions Inc. be liable for any damages whatsoever (including without limitation to damages for loss of business profits, loss of business information, business interruption, and the like) arising out of the use of, or inability to use this program even if Clear Creek Solutions Inc. or their authorized representatives have been advised of the possibility of such damages. Software Copyright © by : Clear Creek Solutions, Inc. 2005-2025; All Rights Reserved. Clear Creek Solutions, Inc. 6200 Capitol Blvd. Ste F Olympia, WA. 98501 Toll Free 1(866)943-0304 Local (360)943-0304 www.clearcreeksolutions.com APPENDIX -CTESC PLAN PROPERTY LINE = 165.97' PROPERTY LINE = 165.97' BSBL = 20.0' PR O P E R T Y L I N E = 2 3 0 . 0 ' BS B L = 5 . 0 ' PR O P E R T Y L I N E = 2 3 0 . 0 ' BS B L = 5 . 0 ' BSBL = 20.0' AREA OF WORK SE 176TH ST LANDSCAPE EXIST LIVING QUARTERS (REFER TO OTHER PERMITTED STRUCT.) U. D E C K L. D E C K 45'-10"89'-3"20'-0 " 45'-1 1 " 148'- 5 " 472 4 7 0 466 470 464 46 0 45 8 4 5 6 4 5 4 4 5 2 4 5 0 44 8 4 4 6 4 4 4 44 2 46 8 4 6 6 46 4 462 46 0 458 4 5 6 454 45 2 x x x x x x x x x x x x x x x x x x x x S D S D S D OH P OH P OH P OH P OH P OH PBIKE RACK (5-11 BICYCLES) 30' - 11". 10' LANDSCAPE BUFFER 46 8 5'-0" 18'-0"9'-0" 2 1 8 7 6 9 10 5 4 3 46 2 ELEC. VEHICLE CHARGING STATION WD FENCED TRASH ENCLOSURE 72'- 0 " (8) S T A N D A R D S T A L L S @ 9 ' - 0 " E A . 9'-0"33'-6 1/2"+/- LOW RETAINING WALL GARDEN AREA 100'- 0 " VE G E T A T I O N F L O W P A T H 100 ' - 0 " VE G E T A T I O N F L O W P A T H 2' WIDE 20' LON G D I S P E R S I O N TRENCH - BMP SHEET FLOW DISPERSION - BMP SL O P E I S 1 0 % SL O P E I S 1 0 % N SILT FENCE HI-VIS. FENCE CONSTRUCTION ENTRANCE CATCH BASIN INLET PROTECTION SILT FENCE HI-VIS FENCE CONSTRUCTION ENTRANCE CB - INLET PROTECTION BO D E T E M P L E CO M M E R C I A L I N T E R . RE N O V A T I O N & R O O F R E P . 11 4 1 0 S E P E T R O V I T S K Y R D RE N T O N , W A 9 8 0 5 5 TE S C P L A N 1"=30'-00" U.N.O 12/22/2025DATE: PR O J E C T : SCALE: DWG. NO.: SK Y G A T E E N G I N E E R S A N D CO N S U L T A N T S L L C , KE R E L L O S Y O U S S E F , P . E . 21 6 1 9 3 6 T H D R S E - B O T H E L L W A , 9 8 0 2 1 PH O N E : ( 4 2 5 ) 6 2 3 - 4 6 1 9 KE R E L L O S . Y @ S K Y G A T E N G I N E E R I N G . C O M SHEET C-2 APPENDIX - D CURRENT SURVEY MAPPING PLAN APPENDIX - E SOIL REPORT APPENDIX-F KING COUNTY GIS MAP King County King County iMap Date: 12/12/2025 Notes: The information included on this map has been compiled by King County staff from a variety of sources and is subject to changewithout notice. King County makes no representations or warranties, express or implied, as to accuracy, completeness, timeliness,or rights to the use of such information. This document is not intended for use as a survey product. King County shall not be liablefor any general, special, indirect, incidental, or consequential damages including, but not limited to, lost revenues or lost profitsresulting from the use or misuse of the information contained on this map. Any sale of this map or information on this map isprohibited except by written permission of King County.±