The URL can be used to link to this page

Home My WebLink AboutRS_Apron E _ TIR_190626_v1.pdf Technical Information Report for Boeing Commercial Airplanes Apron E Stalls and Paint Hangar Prepared for: Boeing Commercial Airplanes, Seattle District P.O. Box 3707, M/S: 1W-10 Seattle, Washington 98124 Prepared by: 8410 154th Avenue NE, Suite 120 Redmond, WA 98052 Tele: (425) 869-2670 FAX: (425) 869-2679 60% Design Submittal June 2019 This report has been prepared by the staff of DOWL under the direction of the undersigned professional engineer whose stamp and signature appears hereon. 13726.16 Table of Contents 1.0 PROJECT OVERVIEW .................................................................................................................... 5 Figure 1: TIR Worksheet ......................................................................................................................................... 6 Figure 2: Vicinity Map .......................................................................................................................................... 11 Figure 3: Drainage Basin Map .............................................................................................................................. 12 Figure 4: Soils Mapping ........................................................................................................................................ 13 2.0 CONDITIONS & REQUIREMENTS SUMMARY ................................................................. 16 3.0 OFF-SITE ANALYSIS .................................................................................................................... 19 3.1 Define and Map the Study Area .................................................................................................................. 19 3.2 Review All Available Information On the Study Area .................................................................................. 19 3.3 Field Inspect the Study Area ....................................................................................................................... 19 3.4 Describe the Drainage System .................................................................................................................... 19 Figure 5: Downstream Flow Path to Lake Washington ......................................................................................... 20 Figure 6: Flood Map ............................................................................................................................................. 21 Figure 7: Critical Areas Map ................................................................................................................................. 22 4.0 FLOW CONTROL & WATER QUALITY FACILITY ANALYSIS & DESIGN ................................ 23 4.1 Existing Site Hydrology ............................................................................................................................... 23 4.2 Developed Site Hydrology .......................................................................................................................... 24 4.3 Flow Control ............................................................................................................................................... 24 4.4 On-Site Flow Control BMPS ........................................................................................................................ 24 4.5 Water Quality ............................................................................................................................................. 25 Figure 8: Existing Conditions ................................................................................................................................ 26 Figure 9: Proposed Conditions ............................................................................................................................. 27 5.0 CONVEYANCE SYSTEM ANALYSIS & DESIGN ......................................................................... 28 6.0 SPECIAL REPORTS & STUDIES .................................................................................................. 29 7.0 OTHER PERMITS ......................................................................................................................... 30 8.0 CWSPPP ANALYSIS AND DESIGN ............................................................................................. 31 8.1 Erosion and Sediment Control (ESC) Measures ........................................................................................... 31 8.1.1 Clearing Limits .......................................................................................................................................... 31 8.1.2 Cover Measures ........................................................................................................................................ 31 8.1.3 Perimeter Protection ................................................................................................................................ 31 8.1.4 Traffic Area Stabilization ........................................................................................................................... 31 8.1.5 Sediment Retention .................................................................................................................................. 31 8.1.6 Surface Water Collection .......................................................................................................................... 31 8.1.7 Dewatering Control .................................................................................................................................. 31 8.1.8 Dust Control .............................................................................................................................................. 32 8.1.9 Flow Control ............................................................................................................................................. 32 8.1.10 Control Pollutants ................................................................................................................................ 32 8.1.11 Protect Existing and Proposed Flow Control BMPS ............................................................................. 32 8.1.12 Maintain BMPs ..................................................................................................................................... 32 8.1.13 Manage the Project ............................................................................................................................. 32 8.2 SWPPS Measures ........................................................................................................................................ 32 8.2.1 Pollutant Handling and Disposal ............................................................................................................... 32 8.2.2 Cover and Containment for Materials, Fuel and Other Pollutants ........................................................... 33 8.2.3 Manage the Project Site ........................................................................................................................... 33 8.2.4 Protect from Spills and Drips .................................................................................................................... 33 8.2.5 Avoid Overapplication or Untimely Application of Chemicals and Fertilizers .......................................... 33 8.2.6 Prevent or Treat Contamination of Stormwater Runoff ........................................................................... 33 8.3 SWPPP Plan Design ..................................................................................................................................... 33 8.3.1 Element 1 – Preserve Vegetation / Mark Clearing Limits ......................................................................... 33 8.3.2 Element 2 – Establish Construction Access .............................................................................................. 34 8.3.3 Element 3 – Control Flow Rates ............................................................................................................... 34 8.3.4 Element 4 – Install Sediment Controls ..................................................................................................... 34 8.3.5 Element 5 – Stabilize Soils ........................................................................................................................ 34 8.3.6 Element 6 – Protect Slopes ....................................................................................................................... 34 8.3.7 Element 7 – Protect Drain Inlets ............................................................................................................... 34 8.3.8 Element 8 – Stabilize Channels and Outlets ............................................................................................. 34 8.3.9 Element 9 – Control Pollutants ................................................................................................................. 34 8.3.10 Element 10 – Control Dewatering ....................................................................................................... 35 8.3.11 Element 11 – Maintain BMPs............................................................................................................... 35 8.3.12 Element 12 – Manage the Project ....................................................................................................... 35 8.3.13 Element 13 – Protect Low Impact Development (LID)......................................................................... 35 9.0 BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT .......... 36 9.1 Bond Quantities .......................................................................................................................................... 36 9.2 Flow Control and Water Quality Facility Summary Sheet and Sketch.......................................................... 36 9.3 Declaration of Covenant for Privately Maintained Flow Control and Water Quality Facilities .................... 36 10.0 OPERATIONS & MAINTENANCE MANUAL ............................................................................. 37 Appendix A CSWPPP Plans Appendix B WWHM Report Appendix C Water Quality Treatment Standard Detail 5 1.0 PROJECT OVERVIEW This Technical Information Report is submitted to the City of Renton in support of the Apron E Expansion Project on the existing parking lot proposed by Boeing. The project proposes to construct three airplane stalls, a paint hangar, and a utility maintenance building on the existing parking lot. The Apron E Expansion Project area is located at the intersection of Logan Ave N and N 6th St, adjacent to the Apron D project site. The existing parking lot is situated between the Apron D project area and Logan Ave N. The northern boundary of the lot is adjacent to N 6th St. The project will use the 2017 Renton Surface Water Design Manual (RSWDM). The project is required to undergo a Full Drainage Review in accordance with Figure 1.1.2.A of the RSWDM since it will be removing or replacing over 2,000 square feet of impervious surface. The project is located on the east side of the Cedar River, which flows north towards Lake Washington. The project area will discharge directly into Lake Washington. For this project threshold discharge area (TDA 1), flow control is not required since the proposed system connects into an existing system that is considered to be exempt from flow control. The project will provide enhanced water quality treatment by implementing MWS-Linear Modular Wetland structures upstream of the discharge point. The projects consists of urban land per the USDA soil map. Information Provided: Figure 1: TIR Worksheet Figure 2: Vicinity Map Figure 3: Drainage Basin Map Figure 4: Soils Mapping 6 Figure 1: TIR Worksheet 11 Figure 2: Vicinity Map APRON E - STALLS PHASE 1 PROJECT VICINITY MAP WWW.DOWL.COM FIGURE 2 PROJECT SITE 12 Figure 3: Drainage Basin Map BOEING 737-MAX10BOEING 737-MAX101694 SF ELECTRICAL ROOM 11A1 767 SF COMPRESSOR ROOM 11A2 1522 SF BOILER ROOM 11A3 1294 SF INDUSTRIAL WASTE TANK ROOM 11A4 GV 1 APRON E - STALLS PHASE 1 DRAINAGE BASIN MAP WWW.DOWL.COM 1 FIGURE 3 13 Figure 4: Soils Mapping 16 2.0 CONDITIONS & REQUIREMENTS SUMMARY Existing Conditions The Apron E Expansion project area is located at the intersection of Logan Ave N and N 6th St, adjacent to the Apron D project site. The existing parking lot is situated between the Apron D project area and Logan Ave N. The northern boundary of the lot is adjacent to N 6th St. The existing project area is currently being uses as a parking lot with existing utilities in place. The existing parking lot is a mix of old concrete and asphalt pavement along with existing lighting and drainage structures. The storm system currently discharges to the existing storm system located in Apron D just west of the project site. The existing onsite storm system will be removed and replaced with the proposed storm drain system that will collect and convey runoff from the new apron facilities. The new storm lines will tie into the existing storm system. The existing system discharges to a storm drain interceptor pipe system which runs north, parallel with the Cedar River and eventually discharges into Lake Washington. The project site is gently sloped and surfaced primarily with concrete and asphalt pavement, with minimal grass landscaping. Site soils are classified as Urban Land, Ur. Figure 3 is a soil map from the USDA Web Soil Survey. Full Drainage Review This project includes more than 2,000 square feet of new and replaced impervious surface. Therefore, the project is subject to a full drainage review and must satisfy all 9 Core Requirements and 6 Special Requirements of the RSWDM. The following summary describes how this project will meet the “Core Requirements” and “Special Requirements” that apply according to Section 1.2 in the RSWDM. RSWDM Core Requirements 1. Core Requirement #1: Discharge at the Natural Location The project area will continue to discharge into the existing storm system within Apron D but will modify the on-site storm system in order to convey runoff to the discharge point. The project area can be considered to be one TDA since all runoff from the site converges at a single discharge point. 2. Core Requirement #2: Off-Site Analysis See Section 3.0 for a detailed discussion on off-site analysis. The project is required to provide a Level 1 downstream analysis as described in Section 1.2.2.1 of the RSWDM. 3. Core Requirement #3: Flow Control See Section 4.0 for a detailed discussion on flow control facilities for the project. The project is exempt from the flow control provisions since the 17 proposed storm system connects into an existing system that discharges into a flow control exempt waterbody. 4. Core Requirement #4: Conveyance System Under this core requirement, new pipe systems must be analyzed for capacity to contain and convey at minimum the 25-year peak flow. The proposed drainage system will be sized to convey and contain the 25-year peak flow. See Section 5.0 for a detailed discussion on conveyance. 5. Core Requirement #5: Erosion & Sediment Control Temporary erosion and sediment control will be provided for the project. A Temporary Erosion and Sediment Control Plan (TESC) has been prepared and included in the plan set. CSWPP is covered under Section 8.0 of this report. 6. Core Requirement #6: Maintenance and Operations See Section 10.0 of this report for a detailed discussion on maintenance and operations. Ownership of the existing stormwater system (Boeing Renton) will not change and the current maintenance program will remain in place. The site is staffed 24-hours a day, there is a central monitoring system in place providing for timely notification of problems. 7. Core Requirement #7: Financial Guarantees and Liability The project will comply with financial guarantees as required by the City of Renton. 8. Core Requirement #8: Water Quality The project area is above the 5,000 square foot threshold for providing water quality treatment. The project location is considered an industrial site. Therefore, Enhanced Basic Water Quality is required per the latest King County Water Quality Applications Map. The project will implement MWS-Linear Modular Wetland structures upstream of the discharge point. 9. Core Requirement #9: On-Site BMPS The project is required to apply on-site flow control BMPs to new impervious surfaces. See Section 4.0 for a detailed discussion regarding on-site flow control BMPs. City of Renton Special Requirements 1. Special Requirement #1: Other Adopted Area-Specific Requirements The site is not located within an area having specific requirements above and beyond the core requirements. 2. Special Requirement #2: Flood Hazard Area Delineation The project site is not within the 100- year floodplain. This project is located Zone X Other Flood Areas, 500-year floodplain per the City of Renton (COR) mapping. See Figure 5. 3. Special Requirement #3: Flood Protection Facilities This project does not propose to rely on an existing flood protection facility nor does it modify or construct a new flood protection facility. 18 4. Special Requirement #4: Source Control This project does warrant source controls. Fuel spill control and containment will be provided for those areas that might hold a fueled or previously fueled aircraft. 5. Special Requirement #5: Oil Control For a redevelopment project, where the threshold of new plus replaced pollution generating impervious surfaces of 5,000 square feet is exceeded, runoff treatment is required. The project will implement two Baffle Oil-Water Separator structures upstream of the discharge point. 6. Special Requirement #6: Aquifer Protection Area The project is not located in an Aquifer Protection Area Zone per City of Renton Groundwater Protection Areas (printed 11/12/2014) provided in the City of Renton Surface Water Design Manual (SWDM) Special Requirements. 19 3.0 OFF-SITE ANALYSIS Per RSWDM Section 1.2.2, this project must provide an off-site analysis report that assesses potential off- site drainage and water quality impacts associated with the improvements to the project site. The project requires a Level 1 downstream analysis as described in Section 1.2.2.1 of the RSWDM. 3.1 Define and Map the Study Area The project site has a single discharge point to the west of the project site, which connects into the existing storm system in Apron D. The project will maintain the existing discharge point. See Figure 4 for the downstream flow path map. 3.2 Review All Available Information On the Study Area City of Renton mapping and data were reviewed. There are no drainage complaints listed within ¼ mile of the project site. The Department of Ecology 303d listings were reviewed for Lake Washington. Some of the listings include Bacteria and Total Phosphorus. The USDA soils map identifies the on-site soils as Urban land. 3.3 Field Inspect the Study Area The downstream flow path from the single discharge point was inspected using the City of Renton GIS Map. No field inspections were completed for this project. There is no evidence of existing drainage and water quality problems at the project site or downstream of the discharge points. The project area discharges into the existing storm system in Apron D, just west of the project site. The existing system conveys flow to a storm drain interceptor pipe system which runs north, parallel with the Cedar River. The interceptor begins as a 24-inch diameter pipe which gradually upsizes to a 60-inch diameter pipe as flow travels north. The pipe system discharges directly into Lake Washington. 3.4 Describe the Drainage System There is no evidence of existing drainage and water quality problems at the project site or downstream of the discharge points. The project will not implement any flow control facilities for the proposed improvements. There are no predicted or anticipated drainage problems at the project site. 20 Figure 5: Downstream Flow Path to Lake Washington Do w nstream An alysis M ap 1000 ft N➤➤N © 2018 Google © 2018 Google © 2018 Google 21 Figure 6: Flood Map 9,028 752 City of Renton Flood Map This map is a user generated static output from an Internet mapping site and is for reference only. Data layers that appear on this map may or may not be accurate, current, or otherwise reliable. 6/18/2019 Legend 5120256 THIS MAP IS NOT TO BE USED FOR NAVIGATION Feet Notes 512 WGS_1984_Web_Mercator_Auxiliary_Sphere City and County Labels City and County Boundary Parcels Floodway Special Flood Hazard Areas (100 year flood) Other Flood Areas (Zone X - 500 year flood) Channel Migration Zones (CMZ) as mapped by King County Moderate Hazard Area Natural Shoreline High Intensity Shoreline Isolated High Intensity Shoreline Residential Urban Conservancy Jurisdictions Streams (Classified) <all other values> Type S Shoreline Type F Fish 22 Figure 7: Critical Areas Map 9,028 752 City of Renton Critical Areas Map This map is a user generated static output from an Internet mapping site and is for reference only. Data layers that appear on this map may or may not be accurate, current, or otherwise reliable. 5/22/2019 Legend 5120256 THIS MAP IS NOT TO BE USED FOR NAVIGATION Feet Notes 512 WGS_1984_Web_Mercator_Auxiliary_Sphere City and County Boundary Parcels Erosion Hazard - High Floodway Special Flood Hazard Areas (100 year flood) Seismic Hazard Areas Faults Streets Parks Waterbodies Map Extent2010 23 4.0 FLOW CONTROL & WATER QUALITY FACILITY ANALYSIS & DESIGN 4.1 Existing Site Hydrology The existing project area is currently being uses as a parking lot with existing utilities in place. The existing parking lot is a mix of old concrete and asphalt pavement along with existing lighting and drainage structures. The project site is gently sloped, with minimal grass landscaping on-site. See Figure 7 for an existing conditions map. The project area can be considered to be one TDA since all runoff from the site converges at a single discharge point. The storm system currently discharges to the existing storm system located in Apron D just west of the project site. The existing system discharges to a storm drain interceptor pipe system which runs north, parallel with the Cedar River and eventually discharges into Lake Washington. The total area of the TDA is 10.13 acres. See Table 1 for the summary of areas in the existing conditions. Table 1: Existing Site Area Summary Existing Impervious Surface 9.13 Acres Existing Pervious Surface 1.00 Acres Total 10.13 Acres 24 4.2 Developed Site Hydrology The Apron E Expansion project proposes to construct three airplane stalls, a paint hangar, and a utility maintenance building on the existing parking lot. The project proposes to convey all stormwater facilities to the existing storm system located in Apron D. The project will continue to discharge into the existing storm system within Apron D but will modify the on-site storm system in order to convey runoff to the discharge point. In the developed condition, the project area is still one TDA since all stormwater runoff from the site converges at a single discharge point. The proposed storm system will convey flow to the existing storm system in Apron D, which connects to a storm drain interceptor pipe system that runs north, parallel with the Cedar River and discharges into Lake Washington. Flow control facilities will not be implemented on- site. The project area in the developed condition will consist of primarily replaced impervious surfaces, along with new impervious and landscape areas. See Table 2 for the summary of areas in the developed condition. Table 2: Developed Site Area Summary New Impervious Surface 0.70 Acres Replaced Impervious Surface 8.54 Acres New Pervious Surface 0.89 Acres Total 10.13 Acres 4.3 Flow Control The project area is currently tributary to the existing storm system in Apron D. The project will continue to discharge into the existing storm system within Apron D but will modify the on-site storm system in order to convey runoff to the discharge point. The existing storm system directly discharges into Lake Washington, which is considered a flow control exempt waterbody. Since the project will connect into an existing system that discharges out to Lake Washington, the proposed project area shall be exempt from flow control. Flow control facilities will not be implemented on-site. In addition to connecting into an existing flow control exempt system, the project threshold discharge area (TDA) does not generate more than a 0.15 cfs increase in the developed condition when modeled using 15 minute time steps in WWHM. The 100-year peak flow rates for the predeveloped and developed condition are 7.31 and 7.37 cfs, respectively, which results in a difference of 0.06 cfs. According to Section 1.2.3 of the RSWDM, the project area is exempt form flow control requirements since the proposed development only results in an increase of 0.06 cfs. See Appendix B for the report generated in WWHM. 4.4 On-Site Flow Control BMPS Per Core Requirement #9 of the RSWDM, the project is required to apply on-site flow control BMPs. On- site flow control BMPs will not be feasible within the project area due to the lack of pervious surfaces and 25 sufficient space on-site. The implementation of on-site flow control BMPs would not be practical since the project area is located within an airport, where the majority of the site consists of impervious land cover. 4.5 Water Quality Since the project area will be adding more than 5,000 square feet of new impervious surface, the project is required to provide water quality treatment on-site. The project will implement MWS-Linear Modular Wetland structures upstream of the discharge point for two separate storm drain lines. The project site is divided into the North and South drainage basins. See Figure 3 for the Drainage Basin map. The North drainage basin consists of 3.43 acres of impervious surface and generates an off-line water quality flow rate of 0.3148 cfs. The South drainage basin consists of 4.33 acres of impervious surface and generates an off-line water quality flow rate of 0.3975 cfs. The South drainage basin will collect half of the proposed building’s roof runoff and route it to the water quality treatment structure. The other half o f the roof runoff will be bypassing the water quality treatment structure and routed directly to the discharge point. The WWHM reports for the water quality flow rates for each basin can be found in Appendix B. See Appendix C for the MWS-Linear Modular Wetland standard detail. 26 Figure 8: Existing Conditions RENTON SITE PAVEMENT REMOVAL AND TESC PLAN C224R C15 60% DESIGN REVIEW NOT FOR CONSTRUCTION REMOVAL RENTON SITE PAVEMENT REMOVAL AND TESC PLAN C225R C16 60% DESIGN REVIEW NOT FOR CONSTRUCTION REMOVAL RENTON SITE PAVEMENT REMOVAL AND TESC PLAN C226R C17 60% DESIGN REVIEW NOT FOR CONSTRUCTION REMOVAL RENTON SITE PAVEMENT REMOVAL AND TESC PLAN C227R C18 60% DESIGN REVIEW NOT FOR CONSTRUCTION REMOVAL RENTON SITE PAVEMENT REMOVAL AND TESC PLAN C228R C19 60% DESIGN REVIEW NOT FOR CONSTRUCTION REMOVAL RENTON SITE PAVEMENT REMOVAL AND TESC PLAN C229R C20 60% DESIGN REVIEW NOT FOR CONSTRUCTION REMOVAL 27 Figure 9: Proposed Conditions RENTON SITE SITE PLAN C3 C1 GALVANIZATION NOTE LAND USE PERMIT/SEPA NOT FOR CONSTRUCTION GV Inlet Outlet CONTROL POINT TABLE RENTON SITE SITE PLAN C4 C2 GALVANIZATION NOTE LAND USE PERMIT/SEPA NOT FOR CONSTRUCTION CONTROL POINT TABLE LAND USE PERMIT/SEPA NOT FOR CONSTRUCTION RENTON SITE SITE PLAN C5 C3 GALVANIZATION NOTE 28 5.0 CONVEYANCE SYSTEM ANALYSIS & DESIGN In accordance with the RSWDM, pipe capacities for conveyance systems will be analyzed by applying the 25-year peak flow rate. A conveyance system capacity analysis will be provided with the 90% plans. 29 6.0 SPECIAL REPORTS & STUDIES • Stormwater Pollution Prevention Plan (SWPPP) (Appendix A) 30 7.0 OTHER PERMITS The following permits are anticipated for this project: • SEPA Permit • Civil Construction Permit • Building Permit 31 8.0 CWSPPP ANALYSIS AND DESIGN 8.1 Erosion and Sediment Control (ESC) Measures 8.1.1 Clearing Limits Prior to beginning earth disturbing activities on the site, the Contractor shall delineate the clearing limits which will be spray painted with white paint on the edge of the existing concrete panels to be removed. During the construction period, no disturbance beyond the marked clearing limits shall be permitted. The marking shall be maintained by the Contractor for the duration of construction. 8.1.2 Cover Measures The existing asphalt and concrete will remain in place as long as possible. Any exposed disturbed soil will need to be stabilized at the end of each shift. Plastic covering is the most practical means of accomplishing this. 8.1.3 Perimeter Protection The perimeter will have a temporary safety fence. In the perimeter areas on the downhill side a triangular silt dike is to be installed. This triangular silt dike works similar to a silt fence but can easily be installed on existing pavement. The filter fabric traps the sediment so that it can be removed after reaching a depth of four inches. 8.1.4 Traffic Area Stabilization Currently this access is paved, and will be used as existing pavement as long as possible. Once the asphalt is removed, a construction entrance will be installed. If the construction entrance is not providing enough protection then a wheel wash will be installed. 8.1.5 Sediment Retention It is not anticipated that the site will generate significant quantities of sediment laden runoff. The project will utilize storm drain inlet protection and localized TESC measures to prevent sediment laden water leaving the site. Triangular silt dike will also be installed adjacent to all disturbed areas to minimize the transport of sediment. 8.1.6 Surface Water Collection Surface water will be collected by the proposed storm system. Catch basins and clean outs will be used to collect and convey stormwater runoff. The construction area will discharge into the existing storm system located in Apron D, directly west of the project site. 8.1.7 Dewatering Control Based on groundwater elevations, dewatering is not anticipated at the site. 32 8.1.8 Dust Control If dust becomes a problem, then the area shall be sprayed with water until wet, but no runoff shall be generated by spraying. 8.1.9 Flow Control Flow control will not be provided for this project on-site. 8.1.10 Control Pollutants The following measures will be taken: • All vehicles, equipment and petroleum product storage/dispensing areas will be inspected regularly to detect any leaks or spills, and to identify maintenance. • Fueling will be conducted on hard pavement. • Spill prevention measures, such as drip pans, will be used when conducting maintenance and repair of vehicles or equipment. • In order to perform emergency repairs on site, temporary plastic will be placed beneath and, if raining, over the vehicle. • Contaminated surfaces shall be cleaned immediately following any discharge or spill incident. • Process water and slurry resulting from concrete work will be prevented from entering waters of the state by implementing Concrete Handling measures (BMP C151), pH neutralization will be utilized if necessary. 8.1.11 Protect Existing and Proposed Flow Control BMPS Protection measures shall be installed to prevent impacts to existing and proposed flow control BMPs. Triangular silt dike and storm drain inlet protection shall be used to protect existing and proposed flow control BMPs. 8.1.12 Maintain BMPs The Contractor shall be responsible for maintaining and repairing all temporary and permanent erosion and sediment control BMPs throughout construction. All temporary erosion and sediment control BMPs shall be removed prior to final construction approval, or within 30 days after achieving final site stabilization. 8.1.13 Manage the Project Construction will take place during the dry season. All BMPs shall be inspected, maintained and repaired as needed throughout all phases of construction. Site inspections and monitoring shall be documented. The contractor shall update the SWPPP as necessary and keep a copy on site at all times. 8.2 SWPPS Measures 8.2.1 Pollutant Handling and Disposal The following measures will be taken: 33 • All vehicles, equipment and petroleum product storage/dispensing areas will be inspected regularly to detect any leaks or spills, and to identify maintenance. • Fueling will be conducted on hard pavement. • Spill prevention measures, such as drip pans, will be used when conducting maintenance and repair of vehicles or equipment. • In order to perform emergency repairs on site, temporary plastic will be placed beneath and, if raining, over the vehicle. • Contaminated surfaces shall be cleaned immediately following any discharge or spill incident. • Process water and slurry resulting from concrete work will be prevented from entering waters of the state by implementing Concrete Handling measures (BMP C151), pH neutralization will be utilized if necessary. 8.2.2 Cover and Containment for Materials, Fuel and Other Pollutants Temporary storage areas shall be located away from vehicular traffic, near the construction entrances, and away from waterways or storm drains. The storage and handling of hazardous materials shall be minimized whenever possible. Construction materials shall be covered in wet weather. 8.2.3 Manage the Project Site See Section 8.1.13 for managing the project. 8.2.4 Protect from Spills and Drips The BMPs listed in Section 8.2.1 and 8.2.2 shall be used to protect from spills and drips. 8.2.5 Avoid Overapplication or Untimely Application of Chemicals and Fertilizers Chemicals and fertilizers shall be prohibited for this project. 8.2.6 Prevent or Treat Contamination of Stormwater Runoff All BMPs listed in Section 8.1 and 8.2 shall be used to prevent contamination of stormwater runoff. 8.3 SWPPP Plan Design The Stormwater Pollution Prevention Plan (SWPPP) is a stand-alone document that describes the Construction Best Management Practices (BMP’s). The SWPPP has been prepared under a separate cover, but is attached in Appendix A of this report. The 13 elements and BMPs recommended are identified below: 8.3.1 Element 1 – Preserve Vegetation / Mark Clearing Limits Prior to beginning earth disturbing activities on the site, the Contractor shall delineate the clearing limits which will be spray painted with white paint on the edge of the existing concrete panels to be removed. During the construction period, no disturbance beyond the marked clearing limits shall be permitted. The marking shall be maintained by the Contractor for the duration of construction. 34 8.3.2 Element 2 – Establish Construction Access The site is currently paved and the asphalt will remain in place as long as possible. Once the driveway asphalt is removed a construction entrance per the City of Renton standard detail 215.10 could be employed. Sequentially a construction entrance might not be necessary. Wheel washing, street sweeping and street cleaning shall be employed as necessary to prevent sediment from tracking onto the Perimeter Road. 8.3.3 Element 3 – Control Flow Rates Flow control will not be provided for this project on-site. 8.3.4 Element 4 – Install Sediment Controls It is not anticipated that the site will generate significant quantities of sediment laden runoff. The project will utilize storm drain inlet protection and localized TESC measures to prevent sediment laden water leaving the site. Triangular silt dike will also be installed adjacent to all disturbed areas to minimize the transport of sediment. 8.3.5 Element 5 – Stabilize Soils The existing asphalt and concrete will remain in place as long as possible. Exposed and unworked soils shall be stabilized with Plastic Coverings per City of Renton standard detail 213.30 or an equivalent protection. 8.3.6 Element 6 – Protect Slopes The site is relatively flat, where there are no slopes. 8.3.7 Element 7 – Protect Drain Inlets Storm drain inlet protection will be installed per City of Renton standard detail 216.30 on all catch basins located within the construction area and immediately downstream of the project areas. 8.3.8 Element 8 – Stabilize Channels and Outlets The stormwater runoff will be directly released into the existing storm system in Apron D, just west of the project area. 8.3.9 Element 9 – Control Pollutants The following measures will be taken: • All vehicles, equipment and petroleum product storage/dispensing areas will be inspected regularly to detect any leaks or spills, and to identify maintenance. • Fueling will be conducted on hard pavement. • Spill prevention measures, such as drip pans, will be used when conducting maintenance and repair of vehicles or equipment. • In order to perform emergency repairs on site, temporary plastic will be placed beneath and, if raining, over the vehicle. 35 • Contaminated surfaces shall be cleaned immediately following any discharge or spill incident. • Process water and slurry resulting from concrete work will be prevented from entering waters of the state by implementing Concrete Handling measures, pH neutralization will be utilized if necessary. 8.3.10 Element 10 – Control Dewatering Based on groundwater elevations, dewatering is not anticipated at the site. 8.3.11 Element 11 – Maintain BMPs All temporary and permanent Erosion and Sediment Control (ESC) BMPs shall be inspected, maintained and repaired as needed to ensure continued performance of their intended function. 8.3.12 Element 12 – Manage the Project During construction consideration shall be given to removing and replacing the pavement in stages. Site inspections and monitoring will be conducted in accordance with Special Conditions S4 of the CSWGP. The contractor will update the SWPPP as necessary and keep a copy on site at all times. 8.3.13 Element 13 – Protect Low Impact Development (LID) There are no LID BMPs proposed for this project. If it becomes necessary, the BMPs listed in Elements 1- 12 shall be used to protect LID BMPs. 36 9.0 BOND QUANTITIES, FACILITY SUMMARIES, AND DECLARATION OF COVENANT 9.1 Bond Quantities A bond quantities worksheet will be prepared for the 90% submittal. 9.2 Flow Control and Water Quality Facility Summary Sheet and Sketch A bond quantities worksheet will be prepared for the 90% submittal. 9.3 Declaration of Covenant for Privately Maintained Flow Control and Water Quality Facilities A bond quantities worksheet will be prepared for the 90% submittal. 10.0 OPERATIONS & MAINTENANCE MANUAL The Operations and Maintenance Manual will be developed in the future submittal. Appendix A CSWPPP Plans Construction Stormwater General Permit Stormwater Pollution Prevention Plan (SWPPP) for Apron E Stalls and Paint Hangar Prepared for: Prepared for: The Washington State Department of Ecology City of Renton, WA Northwest Regional Office 3190 – 160th Avenue SE Bellevue, WA 98008 Permittee / Owner Developer Operator / Contractor Boeing Commercial Airplanes TBD TBD Project Site Location Renton Municipal Airport City of Renton, WA Certified Erosion and Sediment Control Lead (CESCL) Name Organization Contact Phone Number TBD TBD TBD SWPPP Prepared By Name Organization Contact Phone Number Jason Shrope DOWL 425-869-2670 SWPPP Preparation Date June / 12 / 2019 Project Construction Dates Activity / Phase Start Date End Date TBD TBD TBD P a g e | 1 Table of Contents 1 Project Information .............................................................................................................. 4 1.1 Existing Conditions ...................................................................................................... 4 1.2 Proposed Construction Activities .................................................................................. 4 2 Construction Stormwater Best Management Practices (BMPs) ........................................... 6 2.1 The 13 Elements .......................................................................................................... 6 2.1.1 Element 1: Preserve Vegetation / Mark Clearing Limits ........................................ 6 2.1.2 Element 2: Establish Construction Access ............................................................ 7 2.1.3 Element 3: Control Flow Rates ............................................................................. 8 2.1.4 Element 4: Install Sediment Controls .................................................................... 9 2.1.5 Element 5: Stabilize Soils ....................................................................................10 2.1.6 Element 6: Protect Slopes....................................................................................11 2.1.7 Element 7: Protect Drain Inlets ............................................................................12 2.1.8 Element 8: Stabilize Channels and Outlets ..........................................................13 2.1.9 Element 9: Control Pollutants ...............................................................................14 2.1.10 Element 10: Control Dewatering ..........................................................................16 2.1.11 Element 11: Maintain BMPs .................................................................................17 2.1.12 Element 12: Manage the Project ..........................................................................18 2.1.13 Element 13: Protect Low Impact Development (LID) BMPs .................................21 3 Pollution Prevention Team .................................................................................................22 4 Monitoring and Sampling Requirements ............................................................................23 4.1 Site Inspection ............................................................................................................23 4.2 Stormwater Quality Sampling ......................................................................................23 4.2.1 Turbidity Sampling ...............................................................................................23 4.2.2 pH Sampling ........................................................................................................25 5 Discharges to 303(d) or Total Maximum Daily Load (TMDL) Waterbodies .........................26 5.1 303(d) Listed Waterbodies ..........................................................................................26 5.2 TMDL Waterbodies .....................................................................................................26 6 Reporting and Record Keeping ..........................................................................................27 6.1 Record Keeping ..........................................................................................................27 6.1.1 Site Log Book ......................................................................................................27 6.1.2 Records Retention ...............................................................................................27 6.1.3 Updating the SWPPP ...........................................................................................27 6.2 Reporting ....................................................................................................................28 6.2.1 Discharge Monitoring Reports ..............................................................................28 6.2.2 Notification of Noncompliance ..............................................................................28 P a g e | 2 List of Tables Table 1 – Summary of Site Pollutant Constituents ................................................................. 4 Table 2 – Pollutants ................................................................................................................ 14 Table 3 – pH-Modifying Sources ............................................................................................ 15 Table 4 – Dewatering BMPs .................................................................................................... 16 Table 5 – Management ............................................................................................................ 18 Table 6 – BMP Implementation Schedule .............................................................................. 19 Table 7 – Team Information .................................................................................................... 22 Table 8 – Turbidity Sampling Method .................................................................................... 23 Table 9 – pH Sampling Method .............................................................................................. 25 List of Appendices A. Site Map B. BMP Detail C. Correspondence D. Site Inspection Form E. Construction Stormwater General Permit (CSWGP) F. 303(d) List Waterbodies / TMDL Waterbodies Information G. Contaminated Site Information H. Engineering Calculations P a g e | 3 List of Acronyms and Abbreviations Acronym / Abbreviation Explanation 303(d) Section of the Clean Water Act pertaining to Impaired Waterbodies BFO Bellingham Field Office of the Department of Ecology BMP(s) Best Management Practice(s) CESCL Certified Erosion and Sediment Control Lead CO2 Carbon Dioxide CRO Central Regional Office of the Department of Ecology CSWGP Construction Stormwater General Permit CWA Clean Water Act DMR Discharge Monitoring Report DO Dissolved Oxygen Ecology Washington State Department of Ecology EPA United States Environmental Protection Agency ERO Eastern Regional Office of the Department of Ecology ERTS Environmental Report Tracking System ESC Erosion and Sediment Control GULD General Use Level Designation NPDES National Pollutant Discharge Elimination System NTU Nephelometric Turbidity Units NWRO Northwest Regional Office of the Department of Ecology pH Power of Hydrogen RCW Revised Code of Washington SPCC Spill Prevention, Control, and Countermeasure su Standard Units SWMMEW Stormwater Management Manual for Eastern Washington SWMMWW Stormwater Management Manual for Western Washington SWPPP Stormwater Pollution Prevention Plan TESC Temporary Erosion and Sediment Control SWRO Southwest Regional Office of the Department of Ecology TMDL Total Maximum Daily Load VFO Vancouver Field Office of the Department of Ecology WAC Washington Administrative Code WSDOT Washington Department of Transportation WWHM Western Washington Hydrology Model P a g e | 4 1 Project Information Project/Site Name: Apron E Expansion Project Street/Location: Intersection of Logan Ave N / N 6th St City: Renton State: WA Zip code: 98057 Subdivision: N/A Receiving waterbody: Lake Washington 1.1 Existing Conditions Total acreage (including support activities such as off-site equipment staging yards, material storage areas, borrow areas). Total acreage: 10.45 Acres Disturbed acreage: 10.45 Acres Existing structures: Boeing S1 Parking Lot Landscape topography: Flat Drainage patterns: Parking lot runoff is collected with an existing stormdrain system and conveyed west into the existing storm system on Apron D. Existing Vegetation: Landscaped area throughout and around the perimeter of the existing parking lot. Critical Areas (wetlands, streams, high erosion risk, steep or difficult to stabilize slopes): Seizmic hazard areas. List of known impairments for 303(d) listed or Total Maximum Daily Load (TMDL) for the receiving waterbody: Lake Washington is 303(d) listed for Bacteria and Total Phosphorus. Table 1 includes a list of suspected and/or known contaminants associated with the construction activity. Table 1 – Summary of Site Pollutant Constituents Constituent (Pollutant) Location Depth Concentration None 1.2 Proposed Construction Activities Description of site development (example: subdivision): P a g e | 5 This project proposes to construct three airplane stalls, a paint hangar, and a utility maintenance building on the existing Boeing S1 parking lot. The project porposes to connect to the existing storm system on Apron D, just west of the project site. Construction will impact approximately 10.45 acres. Description of construction activities (example: site preparation, demolition, excavation): The project will include the construction of the following elements: • Clearing and grubbing • Demolition and excavation • Utilities – storm, sewer and water • Impervious surface replacement • Storm drain conveyance connection to existing storm system Description of site drainage including flow from and onto adjacent properties. Must be consistent with Site Map in Appendix A: All stormwater is collected on-site via the proposed storm drain system and conveyed west until it discharges to the existing downstream conveyance system on Apron D. There is no contributing flow from or onto adjacent properties. Description of final stabilization (example: extent of revegetation, paving, landscaping): The site will be stabilized with pavement and landscaping. Contaminated Site Information: Proposed activities regarding contaminated soils or groundwater (example: on-site treatment system, authorized sanitary sewer discharge): There are no proposed activities regarding contaminated soils or groundwater. P a g e | 6 2 Construction Stormwater Best Management Practices (BMPs) The SWPPP is a living document reflecting current conditions and changes throughout the life of the project. These changes may be informal (i.e., hand-written notes and deletions). Update the SWPPP when the CESCL or local agency has noted a deficiency in BMPs or deviation from original design. 2.1 The 13 Elements 2.1.1 Element 1: Preserve Vegetation / Mark Clearing Limits To protect adjacent properties and to reduce the area of soil exposed to construction, the limits of construction will be clearly marked before land-disturbing activities begin. Trees that are to be preserved, as well as all sensitive areas and their buffers, shall be clearly delineated in the field. In general, natural vegetation and native topsoil shall be retained in an undisturbed state to the maximum extent possible. A protective barrier shall be placed aound the protected trees prior to land preparation or construction activities, and shall remain in place until all construction activity is terminated. No equipment, chemicals, soil deposits or construction materials shall be placed within the protective barriers. Any landscaping activities subsequent to the removal of the barriers shall be accomplished with light machinery or hand labor. (LMC 17.15.160 B1) Prior to beginning earth disturbing activities on the site, the Contractor shall delineate the clearing limits which will be spray painted with white paint on the edge of the existing concrete panels to be removed. During the construction period, no disturbance beyond the marked clearing limits shall be permitted. The marking shall be maintained by the Contractor for the duration of construction. List and describe BMPs: • Plastic or Metal Fence (BMP D.2.1.1.1) (if necessary) Installation Schedules: Prior to beginning construction activities Inspection and Maintenance plan: Weekly observation Responsible Staff: Contractor P a g e | 7 2.1.2 Element 2: Establish Construction Access Construction access or activities occurring on unpaved areas shall be minimized, yet where necessary, access points shall be stabilized to minimize the tracking of sediment onto public roads, and wheel washing, street sweeping, and street cleaning shall be employed to prevent sediment from entering state waters. All wash wastewater shall be controlled on site. Currently this access is paved, and will be used as existing pavement as long as possible. Once the asphalt is removed, a construction entrance will be installed. If the construction entrance is not providing enough protection then a wheel wash will be installed. List and describe BMPs: • Stabilized Construction Entrance (BMP D.2.1.4.1) (if necessary) • Construction Road/Parking Area Stabilization (BMP D.2.1.4.2) • Wheel Wash (BMP D.2.1.4.3) (if necessary) Installation Schedules: These will be implemented for the duration of construction Inspection and Maintenance plan: As necessary Responsible Staff: Contractor P a g e | 8 2.1.3 Element 3: Control Flow Rates In order to protect the properties and waterways downstream of the project site, stormwater discharges from the site will be controlled. There are no specific BMPs for flow control that shall be used on this project. The project site is located west of the Cascade Mountain Crest. As such, the project must comply with Core Requirement 3. In general, discharge rates of stormwater from the site will be controlled where increases in impervious area or soil compaction during construction could lead to downstream erosion, or where necessary to meet local agency stormwater discharge requirements (e.g. discharge to combined sewer systems). Flow control will not be provided for this project on-site since the project area is designated as being exempt from flow control requirements. Will you construct stormwater retention and/or detention facilities? Yes No Will you use permanent infiltration ponds or other low impact development (example: rain gardens, bio-retention, porous pavement) to control flow during construction? Yes No List and describe BMPs: N/A Installation Schedules: N/A Inspection and Maintenance plan: N/A Responsible Staff: N/A P a g e | 9 2.1.4 Element 4: Install Sediment Controls All stormwater runoff from disturbed areas shall pass through an appropriate sediment removal BMP before leaving the construction site or prior to being discharged to an infiltration facility. The specific BMPs to be used for controlling sediment on this project include: • Triangular Silt Dike (BMP D.2.1.3.4) • Storm Drain Inlet Protection (BMP D.2.1.5.3) To avoid potential erosion and sediment control issues that may cause a violation(s) of the NPDES Construction Stormwater permit, the Certified Erosion and Sediment Control Lead will promptly initiate the implementation of one or more of the alternative BMPs after the first sign that existing BMPs are ineffective or failing. In addition, sediment will be removed from paved areas in and adjacent to construction work areas manually or using mechanical sweepers, as needed, to minimize tracking of sediments on vehicle tires away from the site and to minimize washoff of sediments from adjacent streets in runoff. Whenever possible, sediment laden water shall be discharged into onsite, relatively level, vegetated areas. Installation Schedules: Prior to beginning construction activities Inspection and Maintenance plan: Weekly inspection and after storm events Responsible Staff: Contractor P a g e | 10 2.1.5 Element 5: Stabilize Soils Exposed and unworked soils shall be stabilized with the application of effective BMPs to prevent erosion throughout the life of the project. The specific BMPs for soil stabilization that shall be used on this project include: • Plastic Covering (BMP D.2.1.2.4) • Dust Control (BMP D.2.1.8) The project site is located west of the Cascade Mountain Crest. As such, no soils shall remain exposed and unworked for more than 7 days during the dry season (May 1 to September 30) and 2 days during the wet season (October 1 to April 30). Regardless of the time of year, all soils shall be stabilized at the end of the shift before a holiday or weekend if needed based on weather forecasts. In general, cut and fill slopes will be stabilized as soon as possible and soil stockpiles will be temporarily covered with plastic sheeting. All stockpiled soils shall be stabilized from erosion, protected with sediment trapping measures, and where possible, be located away from storm drain inlets, waterways, and drainage channels. West of the Cascade Mountains Crest Season Dates Number of Days Soils Can be Left Exposed During the Dry Season May 1 – September 30 7 days During the Wet Season October 1 – April 30 2 days Soils must be stabilized at the end of the shift before a holiday or weekend if needed based on the weather forecast. Anticipated project dates: Start date: TBD End date: TBD Will you construct during the wet season? Yes No Installation Schedules: Implemented as soil is exposed Inspection and Maintenance plan: Daily Responsible Staff: Contractor P a g e | 11 2.1.6 Element 6: Protect Slopes All cut and fill slopes will be designed, constructed, and protected in a manner than minimizes erosion. The project site is relatively flat, where there are no slopes. It is not antipicated to require the protection of slopes, but the following specific BMPs will be used to protect slopes for this project as necessary: • Temporary and Permanent Seeding (BMP D.2.1.2.6) (if necessary) Will steep slopes be present at the site during construction? Yes No Installation Schedules: As necessary – no impacted slopes on-site Inspection and Maintenance plan: As necessary Responsible Staff: Contractor P a g e | 12 2.1.7 Element 7: Protect Drain Inlets All storm drain inlets and culverts made operable during construction shall be protected to prevent unfiltered or untreated water from entering the drainage conveyance system. However, the first priority is to keep all access roads clean of sediment and keep street wash water separate from entering storm drains until treatment can be provided. Storm Drain Inlet Protection (BMP D.2.1.5.3) will be implemented for all drainage inlets and culverts that could potentially be impacted by sediment-laden runoff on and near the project site. If the BMP option listed above are deemed ineffective or inappropriate during construction to satisfy the requirements set forth in the General NPDES Permit, the Certified Erosion and Sediment Control Lead shall implement one or more of the alternative BMP inlet protection options. Installation Schedules: Prior to beginning construction activities Inspection and Maintenance plan: Weekly inspection and after storm events Responsible Staff: Contractor P a g e | 13 2.1.8 Element 8: Stabilize Channels and Outlets Where site runoff is to be conveyed in channels, or discharged to a stream or some other natural drainage point, efforts will be taken to prevent downstream erosion. The specific BMPs for channel and outlet stabilization that shall be used on this project include: • N/A – no channels or outlets on-site or included in project The project site is located west of the Cascade Mountain Crest. As such, all temporary on-site conveyance channels shall be designed, constructed, and stabilized to prevent erosion from the expected peak 10 minute velocity of flow from a Type 1A, 10-year, 24-hour recurrence interval storm for the developed condition. Alternatively, the 10-year, 1-hour peak flow rate indicated by an approved continuous runoff simulation model, increased by a factor of 1.6, shall be used. Stabilization, including armoring material, adequate to prevent erosion of outlets, adjacent streambanks, slopes, and downstream reaches shall be provided at the outlets of all conveyance systems. Provide stabilization, including armoring material, adequate to prevent erosion of outlets, adjacent stream banks, slopes, and downstream reaches, will be installed at the outlets of all conveyance systems. Installation Schedules: N/A Inspection and Maintenance plan:N/A Responsible Staff: N/A P a g e | 14 2.1.9 Element 9: Control Pollutants All pollutants, including waste materials and demolition debris, that occur onsite shall be handled and disposed of in a manner that does not cause contamination of stormwater. Good housekeeping and preventative measures will be taken to ensure that the site will be kept clean, well organized, and free of debris. If required, BMPs to be implemented to control specific sources of pollutants are discussed below. Vehicles, construction equipment, and/or petroleum product storage/dispensing: ▪ All vehicles, equipment, and petroleum product storage/dispensing areas will be inspected regularly to detect any leaks or spills, and to identify maintenance needs to prevent leaks or spills. ▪ Fueling will be conducted on hard pavement. ▪ Spill prevention measures, such as drip pans, will be used when conducting maintenance and repair of vehicles or equipment. ▪ In order to perform emergency repairs on site, temporary plastic will be placed beneath and, if raining, over the vehicle. ▪ Contaminated surfaces shall be cleaned immediately following any discharge or spill incident. ▪ Process water and slurry resulting from concrete work will be prevented from entering water of the state by implementing Concrete Handling measures, pH neutralization will be utilized if necessary. If applicable, the Contractor shall prepare an SPCC Plan according to the Washington State Department of Transportation (WSDOT) Requirements (see the WSDOT Standard Specifications for Road, Bridge, and Municipal Construction 2018). The following pollutants are anticipated to be present on-site: Table 2 – Pollutants Pollutant (List pollutants and source, if applicable) Gasoline – Fuel for vehicles Hydraulic Oil – Operator’s equipment Installation Schedules: Implemented for the duration of construction Inspection and Maintenance plan: Weekly inspection Responsible Staff: Contractor Will maintenance, fueling, and/or repair of heavy equipment and vehicles occur on-site? Yes No P a g e | 15 Will wheel wash or tire bath system BMPs be used during construction? Yes No Will pH-modifying sources be present on-site? Yes No Table 3 – pH-Modifying Sources None Bulk cement Cement kiln dust Fly ash Other cementitious materials New concrete washing or curing waters Waste streams generated from concrete grinding and sawing Exposed aggregate processes Dewatering concrete vaults Concrete pumping and mixer washout waters Recycled concrete Recycled concrete stockpiles Other (i.e., calcium lignosulfate) [please describe: ] Concrete trucks must not be washed out onto the ground, or into storm drains, open ditches, streets, or streams. Excess concrete must not be dumped on-site, except in designated concrete washout areas with appropriate BMPs installed. Excess concrete must be returned to the plant for recycling if there are no concrete washout areas with appropriate BMPs installed. Will uncontaminated water from water-only based shaft drilling for construction of building, road, and bridge foundations be infiltrated provided the wastewater is managed in a way that prohibits discharge to surface waters? Yes No P a g e | 16 2.1.10 Element 10: Control Dewatering All dewatering water from open cut excavation, tunneling, foundation work, trench, or underground vaults shall be discharged into a controlled conveyance system prior to discharge to a sediment trap or sediment pond. Channels will be stabilized, per Element #8. Clean, non- turbid dewatering water will not be routed through stormwater sediment ponds, and will be discharged to systems tributary to the receiving waters of the State in a manner that does not cause erosion, flooding, or a violation of State water quality standards in the receiving water. Highly turbid dewatering water from soils known or suspected to be contaminated, or from use of construction equipment, will require additional monitoring and treatment as required for the specific pollutants based on the receiving waters into which the discharge is occurring. Such monitoring is the responsibility of the contractor. However, the dewatering of soils known to be free of contamination will trigger BMPs to trap sediment and reduce turbidity. At a minimum, geotextile fabric socks/bags/cells will be used to filter this material. To avoid potential erosion and sediment control issues that may cause a violation(s) of the NPDES Construction Stormwater permit, the Certified Erosion and Sediment Control Lead will promptly initiate the implementation of one or more of the alternative BMPs after the first sign that existing BMPs are ineffective or failing. Table 4 – Dewatering BMPs Infiltration Transport off-site in a vehicle (vacuum truck for legal disposal) Ecology-approved on-site chemical treatment or other suitable treatment technologies Sanitary or combined sewer discharge with local sewer district approval (last resort) Use of sedimentation bag with discharge to ditch or swale (small volumes of localized dewatering) Installation Schedules: As necessary – dewatering is not anticipated Inspection and Maintenance plan: As necessary Responsible Staff: Contractor P a g e | 17 2.1.11 Element 11: Maintain BMPs All temporary and permanent Erosion and Sediment Control (ESC) BMPs shall be maintained and repaired as needed to ensure continued performance of their intended function. Maintenance and repair shall be conducted in accordance with each particular BMP specification (see Volume II of the SWMMWW or Chapter 7 of the SWMMEW). Visual monitoring of all BMPs installed at the site will be conducted at least once every calendar week and within 24 hours of any stormwater or non-stormwater discharge from the site. If the site becomes inactive and is temporarily stabilized, the inspection frequency may be reduced to once every calendar month. All temporary ESC BMPs shall be removed within 30 days after final site stabilization is achieved or after the temporary BMPs are no longer needed. Trapped sediment shall be stabilized on-site or removed. Disturbed soil resulting from removal of either BMPs or vegetation shall be permanently stabilized. Additionally, protection must be provided for all BMPs installed for the permanent control of stormwater from sediment and compaction. BMPs that are to remain in place following completion of construction shall be examined and restored to full operating condition. If sediment enters these BMPs during construction, the sediment shall be removed and the facility shall be returned to conditions specified in the construction documents. P a g e | 18 2.1.12 Element 12: Manage the Project The project will be managed based on the following principles: • Projects will be phased to the maximum extent practicable and seasonal work limitations will be taken into account. • Inspection and monitoring: o Inspection, maintenance and repair of all BMPs will occur as needed to ensure performance of their intended function. o Site inspections and monitoring will be conducted in accordance with Special Condition S4 of the CSWGP. Sampling locations are indicated on the Site Map. Sampling station(s) are located in accordance with applicable requirements of the CSWGP. • Maintain an updated SWPPP. o The SWPPP will be updated, maintained, and implemented in accordance with Special Conditions S3, S4, and S9 of the CSWGP. As site work progresses the SWPPP will be modified routinely to reflect changing site conditions. The SWPPP will be reviewed monthly to ensure the content is current. Table 5 – Management Design the project to fit the existing topography, soils, and drainage patterns Emphasize erosion control rather than sediment control Minimize the extent and duration of the area exposed Keep runoff velocities low Retain sediment on-site Thoroughly monitor site and maintain all ESC measures Schedule major earthwork during the dry season Other (please describe) P a g e | 19 Table 6 – BMP Implementation Schedule Phase of Construction Project Stormwater BMPs Date Wet/Dry Season Phase of Construction Project Stormwater BMPs Date Wet/Dry Season P a g e | 20 [Insert construction activity] [Insert BMP] [MM/DD/YYYY] [Insert Season] P a g e | 21 2.1.13 Element 13: Protect Low Impact Development (LID) BMPs The project will not proposed any LID BMPs for this site. If it becomes necessary, the BMPs listed in Elements 1-12 shall be used to protect LID BMPs. P a g e | 22 3 Pollution Prevention Team Table 7 – Team Information Title Name(s) Phone Number Certified Erosion and Sediment Control Lead (CESCL) TBD TBD Resident Engineer TBD 425-869-2670 Emergency Ecology Contact Rob Walls 425-649-7130 Emergency Permittee/ Owner Contact Mark Clement 206-617-2944 Non-Emergency Owner Contact Mark Clement 206-617-2944 Monitoring Personnel TBD TBD Ecology Regional Office Northwest Regional Office 425-649-7000 P a g e | 23 4 Monitoring and Sampling Requirements Monitoring includes visual inspection, sampling for water quality parameters of concern, and documentation of the inspection and sampling findings in a site log book. A site log book will be maintained for all on-site construction activities and will include: • A record of the implementation of the SWPPP and other permit requirements • Site inspections • Stormwater sampling data The site log book must be maintained on-site within reasonable access to the site and be made available upon request to Ecology or the local jurisdiction. The receiving waterbody, Lake Washington, is impaired for: Bacteria and Total Phosphorus. All stormwater and dewatering discharges from the site are subject to an effluent limit of 8.5 su for pH and/or 25NTU for turbidity. 4.1 Site Inspection Site inspections will be conducted at least once every calendar week and within 24 hours following any discharge from the site. For sites that are temporarily stabilized and inactive, the required frequency is reduced to once per calendar month. The discharge point(s) is located at the existing catch basin structure at the west end of the property. 4.2 Stormwater Quality Sampling 4.2.1 Turbidity Sampling Requirements include calibrated turbidity meter or transparency tube to sample site discharges for compliance with the CSWGP. Sampling will be conducted at all discharge points at least once per calendar week. Method for sampling turbidity: Table 8 – Turbidity Sampling Method Turbidity Meter/Turbidimeter (required for disturbances 5 acres or greater in size) Transparency Tube (option for disturbances less than 1 acre and up to 5 acres in size) The benchmark for turbidity value is 25 nephelometric turbidity units (NTU) and a transparency less than 33 centimeters. If the discharge’s turbidity is 26 to 249 NTU or the transparency is less than 33 cm but equal to or greater than 6 cm, the following steps will be conducted: 1. Review the SWPPP for compliance with Special Condition S9. Make appropriate revisions within 7 days of the date the discharge exceeded the benchmark. P a g e | 24 2. Immediately begin the process to fully implement and maintain appropriate source control and/or treatment BMPs as soon as possible. Address the problems within 10 days of the date the discharge exceeded the benchmark. If installation of necessary treatment BMPs is not feasible within 10 days, Ecology may approve additional time when the Permittee requests an extension within the initial 10-day response period. 3. Document BMP implementation and maintenance in the site log book. If the turbidity exceeds 250 NTU or the transparency is 6 cm or less at any time, the following steps will be conducted: 1. Telephone or submit an electronic report to the applicable Ecology Region’s Environmental Report Tracking System (ERTS) within 24 hours. • Northwest Region (King, Kitsap, Island, San Juan, Skagit, Snohomish, Whatcom): (425) 649-7000 or http://www.ecy.wa.gov/programs/spills/forms/nerts_online/NWRO_nerts_online.html 2. Immediately begin the process to fully implement and maintain appropriate source control and/or treatment BMPs as soon as possible. Address the problems within 10 days of the date the discharge exceeded the benchmark. If installation of necessary treatment BMPs is not feasible within 10 days, Ecology may approve additional time when the Permittee requests an extension within the initial 10-day response period 3. Document BMP implementation and maintenance in the site log book. 4. Continue to sample discharges daily until one of the following is true: • Turbidity is 25 NTU (or lower). • Transparency is 33 cm (or greater). • Compliance with the water quality limit for turbidity is achieved. o 1 - 5 NTU over background turbidity, if background is less than 50 NTU o 1% - 10% over background turbidity, if background is 50 NTU or greater • The discharge stops or is eliminated. P a g e | 25 4.2.2 pH Sampling pH monitoring is required for “Significant concrete work” (i.e., greater than 1000 cubic yards poured concrete over the life of the project). The use of recycled concrete or engineered soils (soil amendments including but not limited to Portland cement-treated base [CTB], cement kiln dust [CKD] or fly ash) also requires pH monitoring. For significant concrete work, pH sampling will start the first day concrete is poured and continue until it is cured, typically three (3) weeks after the last pour. For engineered soils and recycled concrete, pH sampling begins when engineered soils or recycled concrete are first exposed to precipitation and continues until the area is fully stabilized. If the measured pH is 8.5 or greater, the following measures will be taken: 1. Prevent high pH water from entering storm sewer systems or surface water. 2. Adjust or neutralize the high pH water to the range of 6.5 to 8.5 su using appropriate technology such as carbon dioxide (CO2) sparging (liquid or dry ice). 3. Written approval will be obtained from Ecology prior to the use of chemical treatment other than CO2 sparging or dry ice. Method for sampling pH: Table 9 – pH Sampling Method pH meter pH test kit Wide range pH indicator paper P a g e | 26 5 Discharges to 303(d) or Total Maximum Daily Load (TMDL) Waterbodies 5.1 303(d) Listed Waterbodies Is the receiving water 303(d) (Category 5) listed for turbidity, fine sediment, phosphorus, or pH? Yes No List the impairment(s): The receiving waterbody, Lake Washington, is impaired for: Bacteria and Total Phosphorus. All stormwater and dewatering discharges from the site are subject to an effluent limit of 8.5 su for pH and/or 25NTU for turbidity 5.2 TMDL Waterbodies Waste Load Allocation for CWSGP discharges: N/A List and describe BMPs: N/A Discharges to TMDL receiving waterbodies will meet in-stream water quality criteria at the point of discharge. The Construction Stormwater General Permit Proposed New Discharge to an Impaired Water Body form is included in Appendix F. P a g e | 27 6 Reporting and Record Keeping 6.1 Record Keeping 6.1.1 Site Log Book A site log book will be maintained for all on-site construction activities and will include: • A record of the implementation of the SWPPP and other permit requirements • Site inspections • Sample logs 6.1.2 Records Retention Records will be retained during the life of the project and for a minimum of three (3) years following the termination of permit coverage in accordance with Special Condition S5.C of the CSWGP. Permit documentation to be retained on-site: • CSWGP • Permit Coverage Letter • SWPPP • Site Log Book Permit documentation will be provided within 14 days of receipt of a written request from Ecology. A copy of the SWPPP or access to the SWPPP will be provided to the public when requested in writing in accordance with Special Condition S5.G.2.b of the CSWGP. 6.1.3 Updating the SWPPP The SWPPP will be modified if: • Found ineffective in eliminating or significantly minimizing pollutants in stormwater discharges from the site. • There is a change in design, construction, operation, or maintenance at the construction site that has, or could have, a significant effect on the discharge of pollutants to waters of the State. The SWPPP will be modified within seven (7) days if inspection(s) or investigation(s) determine additional or modified BMPs are necessary for compliance. An updated timeline for BMP implementation will be prepared. P a g e | 28 6.2 Reporting 6.2.1 Discharge Monitoring Reports Cumulative soil disturbance is one (1) acre or larger; therefore, Discharge Monitoring Reports (DMRs) will be submitted to Ecology monthly. If there was no discharge during a given monitoring period the DMR will be submitted as required, reporting “No Discharge”. The DMR due date is fifteen (15) days following the end of each calendar month. DMRs will be reported online through Ecology’s WQWebDMR System. 6.2.2 Notification of Noncompliance If any of the terms and conditions of the permit is not met, and the resulting noncompliance may cause a threat to human health or the environment, the following actions will be taken: 1. Ecology will be notified within 24-hours of the failure to comply by calling the applicable Regional office ERTS phone number (Regional office numbers listed below). 2. Immediate action will be taken to prevent the discharge/pollution or otherwise stop or correct the noncompliance. If applicable, sampling and analysis of any noncompliance will be repeated immediately and the results submitted to Ecology within five (5) days of becoming aware of the violation. 3. A detailed written report describing the noncompliance will be submitted to Ecology within five (5) days, unless requested earlier by Ecology. Anytime turbidity sampling indicates turbidity is 250 NTUs or greater, or water transparency is 6 cm or less, the Ecology Regional office will be notified by phone within 24 hours of analysis as required by Special Condition S5.A of the CSWGP. • Northwest Region at (425) 649-7000 for Island, King, Kitsap, San Juan, Skagit, Snohomish, or Whatcom County Include the following information: 1. Your name and / Phone number 2. Permit number 3. City / County of project 4. Sample results 5. Date / Time of call 6. Date / Time of sample 7. Project name In accordance with Special Condition S4.D.5.b of the CSWGP, the Ecology Regional office will be notified if chemical treatment other than CO2 sparging is planned for adjustment of high pH water. P a g e | 29 A. Site Map RENTON SITE SITE PLAN C3 C1 GALVANIZATION NOTE LAND USE PERMIT/SEPA NOT FOR CONSTRUCTION GV Inlet Outlet CONTROL POINT TABLE RENTON SITE SITE PLAN C4 C2 GALVANIZATION NOTE LAND USE PERMIT/SEPA NOT FOR CONSTRUCTION CONTROL POINT TABLE LAND USE PERMIT/SEPA NOT FOR CONSTRUCTION RENTON SITE SITE PLAN C5 C3 GALVANIZATION NOTE P a g e | 30 B. BMP Detail The following BMPs will be implemented for this project: • Plastic or Metal Fence (BMP D.2.1.1.1) (if necessary) • Plastic Covering (BMP D.2.1.2.4) • Temporary and Permanent Seeding (BMP D.2.1.2.6) (if necessary) • Triangular Silt Dike (BMP D.2.1.3.4) • Stabilized Construction Entrance (BMP D.2.1.4.1) (if necessary) • Construction Road/Parking Area Stabilization (BMP D.2.1.4.2) • Wheel Wash (BMP D.2.1.4.3) (if necessary) • Storm Drain Inlet Protection (BMP D.2.1.5.3) • Dust Control (BMP D.2.1.8) SECTION D.2.1 ESC MEASURES protection is warranted. Permanent fencing may also be used if desired by the applicant. Silt fence, in combination with survey flagging, is also an acceptable method of marking critical areas and their buffers. D.2.1.1.1 PLASTIC OR METAL FENCE Code: FE Symbol: 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. D.2.1.2 COVER MEASURES 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. 4/24/2016 2016 Surface Water Design Manual – Appendix D D-12 SECTION D.2.1 ESC MEASURES D.2.1.2.4 PLASTIC COVERING Code: PC Symbol: 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. 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. FIGURE D.2.1.2.D PLASTIC COVERING TIRES, SANDBAGS, OR EQUIVALENT MAY BE USED TO WEIGHT PLASTIC SEAMS BETWEEN SHEETS MUST OVERLAP A MINIMUM OF 12" AND BE WEIGHTED OR TAPED TOE IN SHEETING IN MINIMUM 4"X4" TRENCH PROVIDE ENERGY DISSIPATION AT TOE WHEN NEEDED 10' MAX. 10' MAX. 4/24/2016 2016 Surface Water Design Manual – Appendix D D-20 D.2.1.2 COVER MEASURES 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. D.2.1.2.5 STRAW WATTLES Code: SW Symbol: Purpose Wattles are erosion and sediment control barriers consisting of straw wrapped in biodegradable tubular plastic or similar encasing material. Wattles may reduce the velocity and can spread the flow of rill and sheet runoff, and can capture and retain sediment. Straw wattles are typically 8 to 10 inches in diameter and 25 to 30 feet in length. The wattles are placed in shallow trenches and staked along the contour of disturbed or newly constructed slopes. Conditions of Use 1. Install on disturbed areas that require immediate erosion protection. 2. Use on slopes requiring stabilization until permanent vegetation can be established. 3. Can be used along the perimeter of a project, as a check dam in unlined ditches and around temporary stockpiles 4. Wattles can be staked to the ground using willow cuttings for added revegetation. 5. Rilling can occur beneath and between wattles if not properly entrenched, allowing water to pass below and between wattles Design and Installation Specifications 1. It is critical that wattles are installed perpendicular to the flow direction and parallel to the slope contour. 2. Narrow trenches should be dug across the slope, on contour, to a depth of 3 to 5 inches on clay soils and soils with gradual slopes. On loose soils, steep slopes, and during high rainfall events, the trenches should be dug to a depth of 5 to 7 inches, or ½ to 2/3 of the thickness of the wattle. 3. Start construction of trenches and installing wattles from the base of the slope and work uphill. Excavated material should be spread evenly along the uphill slope and compacted using hand tamping or other method. Construct trenches at contour intervals of 3 to 30 feet apart depending on the steepness of the slope, soil type, and rainfall. The steeper the slope the closer together the trenches should be constructed. 4. Install the wattles snugly into the trenches and abut tightly end to end. Do not overlap the ends. 5. Install stakes at each end of the wattle, and at 4 foot centers along the entire length of the wattle. 6. If required, install pilot holes for the stakes using a straight bar to drive holes through the wattle and into the soil. 7. At a minimum, wooden stakes should be approximately ¾ x ¾ x 24 inches. Willow cuttings or 3/8 inch rebar can also be used for stakes. 2016 Surface Water Design Manual – Appendix D 4/24/2016 D-21 SECTION D.2.1 ESC MEASURES D.2.1.2.6 TEMPORARY AND PERMANENT SEEDING Code: SE Symbol: Purpose Seeding is intended to reduce erosion by stabilizing exposed soils. A well-established vegetative cover is one of the most effective methods of reducing erosion. Conditions of Use 1. Seeding shall be used throughout the project on disturbed areas that have reached final grade or that will remain unworked for more than 30 days. 2. Vegetation-lined channels shall be seeded. Channels that will be vegetated should be installed before major earthwork and hydroseeded or covered with a Bonded Fiber Matrix (BFM). 3. Retention/detention ponds shall be seeded as required. 4. At the County's discretion, seeding without mulch during the dry season is allowed even though it will take more than seven days to develop an effective cover. Mulch is, however, recommended at all times because it protects seeds from heat, moisture loss, and transport due to runoff. 5. At the beginning of the wet season, all disturbed areas shall be reviewed to identify which ones can be seeded in preparation for the winter rains (see Section D.2.4.2). Disturbed areas shall be seeded within one week of the beginning of the wet season. A sketch map of those areas to be seeded and those areas to remain uncovered shall be submitted to the DPER inspector. The DPER inspector may require seeding of additional areas in order to protect surface waters, adjacent properties, or drainage facilities. 6. At final site stabilization, all disturbed areas not otherwise vegetated or stabilized shall be seeded and mulched (see Section D.2.4.5). Design and Installation Specifications 1. The best time to seed is April 1 through June 30, and September 1 through October 15. Areas may be seeded between July 1 and August 31, but irrigation may be required in order to grow adequate cover. Areas may also be seeded during the winter months, but it may take several months to develop a dense groundcover due to cold temperatures. The application and maintenance of mulch is critical for winter seeding. 2. To prevent seed from being washed away, confirm that all required surface water control measures have been installed. 3. The seedbed should be firm but not compacted because soils that are well compacted will not vegetate as quickly or thoroughly. Slopes steeper than 3H:1V shall be surface roughened. Roughening can be accomplished in a variety of ways, but the typical method is track walking, or driving a crawling tractor up and down the slope, leaving cleat imprints parallel to the slope contours. 4. In general, 10-20-20 N-P-K (nitrogen-phosphorus-potassium) fertilizer may be used at a rate of 90 pounds per acre. Slow-release fertilizers are preferred because they are more efficient and have fewer environmental impacts. It is recommended that areas being seeded for final landscaping conduct soil tests to determine the exact type and quantity of fertilizer needed. This will prevent the over- application of fertilizer. Disturbed areas within 200 feet of water bodies and wetlands must use slow- release low-phosphorus fertilizer (typical proportions 3-1-2 N-P-K). 5. The following requirements apply to mulching: a) Mulch is always required for seeding slopes greater than 3H:1V (see Section D.2.1.2.2). 4/24/2016 2016 Surface Water Design Manual – Appendix D D-24 D.2.1.2 COVER MEASURES b) If seeding during the wet season, mulch is required. c) The use of mulch may be required during the dry season at the County's discretion if grass growth is expected to be slow, the soils are highly erodible due to soil type or gradient, there is a water body close to the disturbed area, or significant precipitation (see Section D.2.4.2) is anticipated before the grass will provide effective cover. d) Mulch may be applied on top of the seed or simultaneously by hydroseeding. 6. Hydroseeding is allowed as long as tackifier is included. Hydroseeding with wood fiber mulch is adequate during the dry season. During the wet season, the application rate shall be doubled because the mulch and tackifier used in hydroseeding break down fairly rapidly. It may be necessary in some applications to include straw with the wood fiber, but this can be detrimental to germination. 7. Areas to be permanently landscaped shall use soil amendments. Good quality topsoil shall be tilled into the top six inches to reduce the need for fertilizer and improve the overall soil quality. Most native soils will require the addition of four inches of well-rotted compost to be tilled into the soil to provide a good quality topsoil. Compost used should meet specifications provided in Reference 11-C of the SWDM. 8. The seed mixes listed below include recommended mixes for both temporary and permanent seeding. These mixes, with the exception of the wetland mix, shall be applied at a rate of 120 pounds per acre. This rate may be reduced if soil amendments or slow-release fertilizers are used. Local suppliers should be consulted for their recommendations because the appropriate mix depends on a variety of factors, including exposure, soil type, slope, and expected foot traffic. Alternative seed mixes approved by the County may be used. Table D.2.1.2.B presents the standard mix for those areas where just a temporary vegetative cover is required. TABLE D.2.1.2.B TEMPORARY EROSION CONTROL SEED MIX % Weight % Purity % Germination Chewings or red fescue Festuca rubra var. commutata or Festuca rubra 40 98 90 Annual or perennial rye Lolium multiflorum or Lolium perenne 40 98 90 Redtop or colonial bentgrass Agrostis alba or Agrostis tenuis 10 92 85 White dutch clover Trifolium repens 10 98 90 2016 Surface Water Design Manual – Appendix D 4/24/2016 D-25 SECTION D.2.1 ESC MEASURES Table D.2.1.2.C provides just one recommended possibility for landscaping seed. TABLE D.2.1.2.C LANDSCAPING SEED MIX % Weight % Purity % Germination Perennial rye blend Lolium perenne 70 98 90 Chewings and red fescue blend Festuca rubra var. commutata or Festuca rubra 30 98 90 This turf seed mix in Table D.2.1.2.D is for dry situations where there is no need for much water. The advantage is that this mix requires very little maintenance. TABLE D.2.1.2.D LOW-GROWING TURF SEED MIX % Weight % Purity % Germination Dwarf tall fescue (several varieties) Festuca arundinacea var. 45 98 90 Dwarf perennial rye (Barclay) Lolium perenne var. barclay 30 98 90 Red fescue Festuca rubra 20 98 90 Colonial bentgrass Agrostis tenuis 5 98 90 Table D.2.1.2.E presents a mix recommended for bioswales and other intermittently wet areas. Sod shall generally not be used for bioswales because the seed mix is inappropriate for this application. Sod may be used for lining ditches to prevent erosion, but it will provide little water quality benefit during the wet season. TABLE D.2.1.2.E BIOSWALE SEED MIX* % Weight % Purity % Germination Tall or meadow fescue Festuca arundinacea or Festuca elatior 75-80 98 90 Seaside/Creeping bentgrass Agrostis palustris 10-15 92 85 Redtop bentgrass Agrostis alba or Agrostis gigantea 5-10 90 80 * Modified Briargreen, Inc. Hydroseeding Guide Wetlands Seed Mix 4/24/2016 2016 Surface Water Design Manual – Appendix D D-26 D.2.1.2 COVER MEASURES The seed mix shown in Table D.2.1.2.F is a recommended low-growing, relatively non-invasive seed mix appropriate for very wet areas that are not regulated wetlands (if planting in wetland areas, see Section 6.3.1 of the King County Surface Water Design Manual). Other mixes may be appropriate, depending on the soil type and hydrology of the area. Apply this mixture at a rate of 60 pounds per acre. TABLE D.2.1.2.F WET AREA SEED MIX* % Weight % Purity % Germination Tall or meadow fescue Festuca arundinacea or Festuca elatior 60-70 98 90 Seaside/Creeping bentgrass Agrostis palustris 10-15 98 85 Meadow foxtail Alepocurus pratensis 10-15 90 80 Alsike clover Trifolium hybridum 1-6 98 90 Redtop bentgrass Agrostis alba 1-6 92 85 * Modified Briargreen, Inc. Hydroseeding Guide Wetlands Seed Mix The meadow seed mix in Table D.2.1.2.G is recommended for areas that will be maintained infrequently or not at all and where colonization by native plants is desirable. Likely applications include rural road and utility right-of-way. Seeding should take place in September or very early October in order to obtain adequate establishment prior to the winter months. The appropriateness of clover in the mix may need to be considered as this can be a fairly invasive species. If the soil is amended, the addition of clover may not be necessary. TABLE D.2.1.2.G MEADOW SEED MIX % Weight % Purity % Germination Redtop or Oregon bentgrass Agrostis alba or Agrostis oregonensis 40 92 85 Red fescue Festuca rubra 40 98 90 White dutch clover Trifolium repens 20 98 90 Maintenance Standards for Temporary and Permanent Seeding 1. Any seeded areas that fail to establish at least 80 percent cover within one month shall be reseeded. If reseeding is ineffective, an alternate method, such as sodding or nets/blankets, shall be used. If winter weather prevents adequate grass growth, this time limit may be relaxed at the discretion of the County when critical areas would otherwise be protected. 2016 Surface Water Design Manual – Appendix D 4/24/2016 D-27 SECTION D.2.1 ESC MEASURES 2. After adequate cover is achieved, any areas that experience erosion shall be re-seeded and protected by mulch. If the erosion problem is drainage related, the problem shall be fixed and the eroded area re-seeded and protected by mulch. 3. Seeded areas shall be supplied with adequate moisture, but not watered to the extent that it causes runoff. D.2.1.2.7 SODDING Code: SO Symbol: Purpose The purpose of sodding is to establish permanent turf for immediate erosion protection and to stabilize drainage ways where concentrated overland flow will occur. Conditions of Use Sodding may be used in the following areas: 1. Disturbed areas that require short-term or long-term cover 2. Disturbed areas that require immediate vegetative cover 3. All waterways that require vegetative lining (except biofiltration swales—the seed mix used in most sod is not appropriate for biofiltration swales). Waterways may also be seeded rather than sodded, and protected with a net or blanket (see Section D.2.1.2.3). Design and Installation Specifications Sod shall be free of weeds, of uniform thickness (approximately 1-inch thick), and shall have a dense root mat for mechanical strength. The following steps are recommended for sod installation: 1. Shape and smooth the surface to final grade in accordance with the approved grading plan. 2. Amend four inches (minimum) of well-rotted compost into the top eight inches of the soil if the organic content of the soil is less than ten percent. Compost used shall meet compost specifications per SWDM Reference 11-C. 3. Fertilize according to the supplier's recommendations. Disturbed areas within 200 feet of water bodies and wetlands must use non-phosphorus fertilizer. 4. Work lime and fertilizer 1 to 2 inches into the soil, and smooth the surface. 5. Lay strips of sod beginning at the lowest area to be sodded and perpendicular to the direction of water flow. Wedge strips securely into place. Square the ends of each strip to provide for a close, tight fit. Stagger joints at least 12 inches. Staple on slopes steeper than 3H:1V. 6. Roll the sodded area and irrigate. 7. When sodding is carried out in alternating strips or other patterns, seed the areas between the sod immediately after sodding. Maintenance Standards If the grass is unhealthy, the cause shall be determined and appropriate action taken to reestablish a healthy groundcover. If it is impossible to establish a healthy groundcover due to frequent saturation, instability, or some other cause, the sod shall be removed, the area seeded with an appropriate mix, and protected with a net or blanket. 4/24/2016 2016 Surface Water Design Manual – Appendix D D-28 D.2.1.3 PERIMETER PROTECTION D.2.1.3.3 VEGETATED STRIP Code: VS Symbol: Purpose Vegetated strips reduce the transport of coarse sediment from a construction site by providing a temporary physical barrier to sediment and reducing the runoff velocities of overland flow. Conditions of Use 1. Vegetated strips may be used downslope of all disturbed areas. 2. Vegetated strips are not intended to treat concentrated flows, nor are they intended to treat substantial amounts of overland flow. Any concentrated flows must be conveyed through the drainage system to a sediment trap or pond. The only circumstance in which overland flow may be treated solely by a strip, rather than by a sediment trap or pond, is when the area draining to the strip is small (see "Criteria for Use as Primary Treatment" on page D-33). Design and Installation Specifications 1. The vegetated strip shall consist of a 25-foot minimum width continuous strip of dense vegetation with a permeable topsoil. Grass-covered, landscaped areas are generally not adequate because the volume of sediment overwhelms the grass. Ideally, vegetated strips shall consist of undisturbed native growth with a well-developed soil that allows for infiltration of runoff. 2. The slope within the strip shall not exceed 4H:1V. 3. The uphill boundary of the vegetated strip shall be delineated with clearing limits as specified in Section D.2.1.1 (p. D-11). Maintenance Standards 1. Any areas damaged by erosion or construction activity shall be seeded immediately and protected by mulch. 2. If more than 5 feet of the original vegetated strip width has had vegetation removed or is being eroded, sod must be installed using the standards for installation found in Section D.2.1.2.7. If there are indications that concentrated flows are traveling across the buffer, surface water controls must be installed to reduce the flows entering the buffer, or additional perimeter protection must be installed. D.2.1.3.4 TRIANGULAR SILT DIKE (GEOTEXTILE ENCASED CHECK DAM) Code: TSD Symbol: Purpose Triangular silt dikes (TSDs) may be used as check dams, for perimeter protection, for temporary soil stockpile protection, for drop inlet protection, or as a temporary interceptor dike. Silt dikes, if attached to impervious surfaces with tack or other adhesive agent may also be used as temporary wheel wash areas, or concrete washout collection areas. 2016 Surface Water Design Manual – Appendix D 4/24/2016 D-37 SECTION D.2.1 ESC MEASURES Conditions of Use 1. May be used for temporary check dams in ditches. 2. May be used on soil or pavement with adhesive or staples. 3. TSDs have been used to build temporary sediment ponds, diversion ditches, concrete washout facilities, curbing, water bars, level spreaders, and berms. Design and Installation Specifications 1. TSDs must be made of urethane foam sewn into a woven geosynthetic fabric. 2. TSDs are triangular, 10 inches to 14 inches high in the center, with a 20-inch to 28-inch base. A 2- foot apron extends beyond both sides of the triangle along its standard section of 7 feet. A sleeve at one end allows attachment of additional sections as needed 3. Install TSDs with ends curved up to prevent water from flowing around the ends 4. Attach the TSDs and their fabric flaps to the ground with wire staples. Wire staples must be No. 11 gauge wire or stronger and shall be 200 mm to 300 mm in length. 5. When multiple units are installed, the sleeve of fabric at the end of the unit shall overlap the abutting unit and be stapled. 6. TSDs must be located and installed as soon as construction will allow. 7. TSDs must be placed perpendicular to the flow of water. 8. When used as check dams, the leading edge must be secured with rocks, sandbags, or a small key slot and staples. 9. When used in grass-lined ditches and swales, the TSD check dams and accumulated sediment shall be removed when the grass has matured sufficiently to protect the ditch or swale unless the slope of the swale is greater than 4 percent. The area beneath the TSD check dams shall be seeded and mulched immediately after dam removal. Maintenance Standards 1. Triangular silt dikes shall be monitored for performance and sediment accumulation during and after each runoff producing rainfall event. Sediment shall be removed when it reaches one half the height of the silt dike. 2. Anticipate submergence and deposition above the triangular silt dike and erosion from high flows around the edges of the dike/dam. Immediately repair any damage or any undercutting of the dike/dam. D.2.1.3.5 COMPOST BERMS Code: COBE Symbol: Purpose Compost berms are an option to meet the requirements of perimeter protection. Compost berms may reduce the transport of sediment from a construction site by providing a temporary physical barrier to sediment and reducing the runoff velocities of overland flow. Compost berms trap sediment by filtering water passing through the berm and allowing water to pond, creating a settling area for solids behind the berm. Organic materials in the compost can also reduce concentrations of metals and petroleum hydrocarbons from construction runoff. Due to the increase in phosphorous seen in the effluent data from compost berms, they should be used with some cautions in areas that drain to phosphorus sensitive water 4/24/2016 2016 Surface Water Design Manual – Appendix D D-38 SECTION D.2.1 ESC MEASURES D.2.1.4.1 STABILIZED CONSTRUCTION ENTRANCE Code: CE Symbol: 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) 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. 4/24/2016 2016 Surface Water Design Manual – Appendix D D-42 D.2.1.4 TRAFFIC AREA STABILIZATION 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. FIGURE D.2.1.4.A STABILIZED CONSTRUCTION ENTRANCE •PER KING COUNTY ROAD DESIGN AND CONSTRUCTION STANDARDS (KCRDCS), DRIVEWAYS SHALL BE PAVED TO EDGE OF R-O-W PRIOR TO INSTALLATION OF THE CONSTRUCTION ENTRANCE TO AVOID DAMAGING OF THE ROADWAY. •IT IS RECOMMENDED THAT THE ENTRANCE BE CROWNED SO THAT RUNOFF DRAINS OFF THE PAD. 12" MIN. THICKNESS PROVIDE FULL WIDTH OF INGRESS/EGRESS AREA IF A ROADSIDE DITCH IS PRESENT, INSTALL DRIVEWAY CULVERT PER KCRDCS GEOTEXTILE 4"- 8" QUARRY SPALLS R=25' MIN. 100' M I N . EXISTI N G R O A D 15' MIN. NOTES: 2016 Surface Water Design Manual – Appendix D 4/24/2016 D-43 SECTION D.2.1 ESC MEASURES D.2.1.4.2 CONSTRUCTION ROAD/PARKING AREA STABILIZATION Code: CRS Symbol: Purpose Stabilizing subdivision roads, parking areas and other onsite vehicle transportation routes immediately after grading reduces erosion caused by construction traffic or runoff. Conditions of Use 1. Roads or parking areas shall be stabilized wherever they are constructed, whether permanent or temporary, for use by construction traffic. 2. Fencing (see Section D.2.1.1) shall be installed, if necessary, to limit the access of vehicles to only those roads and parking areas that are stabilized. Design and Installation Specifications 1. A 6-inch depth of 2- to 4-inch crushed rock, gravel base, or crushed surfacing base course shall be applied immediately after grading or utility installation. A 4-inch course of asphalt treated base (ATB) may also be used, or the road/parking area may be paved. It may also be possible to use cement or calcium chloride for soil stabilization. If the area will not be used for permanent roads, parking areas, or structures, a 6-inch depth of hog fuel may also be used, but this is likely to require more maintenance. Whenever possible, construction roads and parking areas shall be placed on a firm, compacted subgrade. Note: If the area will be used for permanent road or parking installation later in the project, the subgrade will be subject to inspection. 2. Temporary road gradients shall not exceed 15 percent. Roadways shall be carefully graded to drain transversely. Drainage ditches shall be provided on each side of the roadway in the case of a crowned section, or on one side in the case of a super-elevated section. Drainage ditches shall be designed in accordance with the standards given in Section D.2.1.6.4 (p. D-64) and directed to a sediment pond or trap. 3. Rather than relying on ditches, it may also be possible to grade the road so that runoff sheet-flows into a heavily vegetated area with a well-developed topsoil. Landscaped areas are not adequate. If this area has at least 50 feet of vegetation, then it is generally preferable to use the vegetation to treat runoff, rather than a sediment pond or trap. The 50 feet shall not include vegetated wetlands. If runoff is allowed to sheet flow through adjacent vegetated areas, it is vital to design the roadways and parking areas so that no concentrated runoff is created. 4. In order to control construction traffic, the County may require that signs be erected on site informing construction personnel that vehicles, other than those performing clearing and grading, are restricted to stabilized areas. 5. If construction roads do not adequately reduce trackout to adjacent property or roadways, a wheel wash system will be required. Maintenance Standards Crushed rock, gravel base, hog fuel, etc. shall be added as required to maintain a stable driving surface and to stabilize any areas that have eroded. 4/24/2016 2016 Surface Water Design Manual – Appendix D D-44 D.2.1.4 TRAFFIC AREA STABILIZATION D.2.1.4.3 WHEEL WASH Code: WW Symbol: Purpose Wheel wash systems reduce the amount of sediment transported onto paved roadways and into surface water systems by construction vehicles. Conditions of Use When a stabilized construction entrance is not preventing sediment from being tracked onto pavement: • Wheel washing is generally an effective erosion and sediment control method and BMP when installed with careful attention to topography. For example, a wheel wash can be detrimental if installed at the top of a slope abutting a right-of-way where the water from the dripping truck wheels and undercarriage can run unimpeded into the street. • Pressure washing combined with an adequately sized and properly surfaced wash pad with direct drainage discharge to a large 10 foot x 10-foot sump can be very effective. Design and Installation Specifications A suggested detail is shown in Figure D.2.1.4.B. 1. A minimum of 6inches of asphalt treated base (ATB) over crushed base material or 8 inches over a good subgrade is recommended to pave the wheel wash area. 2. Use a low clearance truck to test the wheel wash before paving. Either a belly dump or lowboy will work well to test clearance. 3. Keep the water level from 12 to 14 inches deep to avoid damage to truck hubs and filling the truck tongues with water. 4. Midpoint spray nozzles are only needed in very muddy conditions. 5. Wheel wash systems should be designed with a small grade change, 6 to 12 inches for a 10-foot wide pond, to allow sediment to flow to the low side of the pond and to help prevent re-suspension of sediment. 6. A drainpipe with a 2 to 3 foot riser should be installed on the low side of the wheel wash pond to allow for easy cleaning and refilling. Polymers may be used to promote coagulation and flocculation in a closed-loop system. 7. Polyacrylamide (PAM) added to the wheel washwater at a rate of 0.25 – 0.5 pounds per 1,000 gallons of water increases effectiveness and reduces cleanup time. If PAM is already being used for dust or erosion control and is being applied by a water truck, the same truck may be used to change the washwater. Maintenance Standards 1. The wheel wash should start out each day with clean, fresh water. 2. The washwater should be changed a minimum of once per day. On large earthwork jobs where more than 10-20 trucks per hour are expected, the washwater will need to be changed more often. 3. Wheel wash or tire bath wastewater shall be discharged to a separate on-site treatment system, such as a closed-loop recirculation system or land application, or to the sanitary sewer system with proper local sewer district approval or permits. 2016 Surface Water Design Manual – Appendix D 4/24/2016 D-45 SECTION D.2.1 ESC MEASURES FIGURE D.2.1.4.B WHEEL WASH AND PAVED CONSTRUCTION ENTRANCE 2% SLOPE 15'15'20'15'50' 18' 12' 3' 5' BUILD 8'x8' SUMP TO ACCOMODATE CLEANING BY TRACKHOE.SECTION A-A NTS 8'x8' SUMP, SEE NOTE LOCATE INVERT OF TOP PIPE 1' ABOVE BOTTOM OF WHEEL WASH DRAIN PIPE 1:1 SLOPE WATER LEVEL ELEVATION VIEW NTS PLAN VIEW NTS 6" SLEEVE CURB ASPHALT CURB ON THE LOW ROAD SIDE TO DIRECT WATER BACK TO POND 6" ATB CONSTRUCTION ENTRANCE 1-1/2" SCHEDULE 40 FOR SPRAYERS 2% SLOPE MIDPOINT SPRAY NOZZLES, IF NEEDED 3" TRASH PUMP WITH FLOATS ON SUCTION HOSE 2" SCHEDULE 40 6" SLEEVE UNDER ROAD 8'x8' SUMP WITH 5' OF CATCH 6" SEWER PIPE WITH BUTTERFLY VALVES 1:1 SLOPE A A 5:1 SLOPE 5:1 SLOPE 15' ATB APRON TO PROTECT GROUND FROM SPLASHING WATER BALL VALVES NOTE: 4/24/2016 2016 Surface Water Design Manual – Appendix D D-46 D.2.1.5 SEDIMENT RETENTION FIGURE D.2.1.5.D SEDIMENT POND RISER DETAIL 3.5' MIN. 18" MIN. 2X RISER DIA. MIN. CORRUGATED METAL RISER CONCRETE BASE ALTERNATIVELY, METAL STAKES AND WIRE MAY BE USED TO PREVENT FLOTATION DEWATERING ORIFICE, SCHEDULE 40 STEEL STUB MIN. DIAMETER AS PER CALCULATIONS 6" MIN. PROVIDE ADEQUATE STRAPPING POLYETHYLENE CAP PERFORATED DEWATERING DEVICE, SEE NOTE WATERTIGHT COUPLING TACK WELD NOTE: PERFORATED CORRUGATED POLYETHYLENE (CPE) DRAINAGE TUBING, DIAMETER MIN. 2" LARGER THAN DEWATERING ORIFICE. TUBING SHALL COMPLY WITH ASTM F667 AND AASHTO M294. D.2.1.5.3 STORM DRAIN INLET PROTECTION Code: FFP or CBI or CBP Symbol: or or Purpose Storm drain inlets are protected to prevent coarse sediment from entering storm drainage systems. Temporary devices around storm drains assist in improving the quality of water discharged to inlets or catch basins by ponding sediment-laden water. These devices are effective only for relatively small drainage areas. Conditions of Use 1. Protection shall be provided for all storm drain inlets downslope and within 500 feet of a disturbed or construction area, unless the runoff that enters the catch basin will be conveyed to a sediment pond or trap. 2. Inlet protection may be used anywhere at the applicant's discretion to protect the drainage system. This will, however, require more maintenance, and it is highly likely that the drainage system will still require some cleaning. 3. The contributing drainage area must not be larger than one acre. Design and Installation Specifications 1. There are many options for protecting storm drain inlets. Two commonly used options are filter fabric protection and catch basin inserts. Filter fabric protection (see Figure D.2.1.5.E) is filter fabric (geotextile) placed over the grate. This method is generally very ineffective and requires intense maintenance efforts. Catch basin inserts (see Figure D.2.1.5.F) are manufactured devices that nest inside a catch basin. This method also requires a high frequency of maintenance to be effective. Both 2016 Surface Water Design Manual – Appendix D 4/24/2016 D-53 SECTION D.2.1 ESC MEASURES options provide adequate protection, but filter fabric is likely to result in ponding of water above the catch basin, while the insert will not. Thus, filter fabric is only allowed where ponding will not be a traffic concern and where slope erosion will not result if the curb is overtopped by ponded water. Trapping sediment in the catch basins is unlikely to improve the water quality of runoff if it is treated in a pond or trap because the coarse particles that are trapped at the catch basin settle out very quickly in the pond or trap. Catch basin protection normally only improves water quality where there is no treatment facility downstream. In these circumstances, catch basin protection is an important last line of defense. It is not, however, a substitute for preventing erosion. The placement of filter fabric under grates is generally prohibited and the use of filter fabric over grates is strictly limited and discouraged. 2. It is sometimes possible to construct a small sump around the catch basin before final surfacing of the road. This is allowed because it can be a very effective method of sediment control. 3. Block and gravel filters, gravel and wire mesh filter barriers, and bag barriers filled with various filtering media placed around catch basins can be effective when the drainage area is 1 acre or less and flows do not exceed 0.5 cfs. It is necessary to allow for overtopping to prevent flooding. Many manufacturers have various inlet protection filters that are very effective in keeping sediment-laden water from entering the storm drainage system. The following are examples of a few common methods. a) Block and gravel filters (Figure D.2.1.5.G) are a barrier formed around an inlet with standard concrete block and gravel, installed as follows: • Height is 1 to 2 feet above the inlet. • Recess the first row of blocks 2 inches into the ground for stability. • Support subsequent rows by placing a 2x4 through the concrete block opening. • Do not use mortar. • Lay some blocks in the bottom row on their side for dewatering the pooled water. • Place cloth or mesh with ½ inch openings over all block openings. • Place gravel below the top of blocks on slopes of 2:1 or flatter. • An alternate design is a gravel donut. b) Gravel and wire mesh filters consist of a gravel barrier placed over the top of an inlet. This structure generally does not provide overflow. Install as follows: • Cloth or comparable wire mesh with ½ inch openings is placed over inlet. • Coarse aggregate covers the cloth or mesh. • Height/depth of gravel should be 1 foot or more, 18 inches wider than inlet on all sides. c) Curb inlet protection with a wooden weir is a barrier formed around an inlet with a wooden frame and gravel, installed as follows: • Construct a frame and attach wire mesh (½ inch openings) and filter fabric to the frame. • Pile coarse washed aggregate against the wire/fabric. • Place weight on frame anchors. d) Curb and gutter sediment barriers (Figure D.2.1.5.H) consist of sandbags or rock berms (riprap and aggregate) 3 feet high and 3 feet wide in a horseshoe shape, installed as follows: • Bags of either burlap or woven geotextile fabric, filled with a variety of media such as gravel, wood chips, compost or sand stacked tightly allows water to pond and allows sediment to separate from runoff. 4/24/2016 2016 Surface Water Design Manual – Appendix D D-54 D.2.1.5 SEDIMENT RETENTION • Leave a "one bag gap" in the top row of the barrier to provide a spillway for overflow. • Construct a horseshoe shaped berm, faced with coarse aggregate if using riprap, 3 x 3 and at least 2 feet from the inlet. • Construct a horseshoe shaped sedimentation trap on the outside of the berm to sediment trap standards for protecting a culvert inlet. 4. Excavated drop inlet sediment traps are appropriate where relatively heavy flows are expected and overflow capability is needed. If emergency overflow is provided, additional end-of-pipe treatment may be required. Excavated drop inlets consist of an excavated impoundment area around a storm drain. Sediment settles out of the stormwater prior to enter the drain. Install according to the following specifications: a) The impoundment area should have a depth of 1 - 2 feet measured from the crest of the inlet structure. b) Side slopes of the excavated area must be no steeper than 2:1. c) Minimum volume of the excavated area should be 35 cubic yards. d) Install provisions for draining the area to prevent standing water problems. e) Keep the area clear of debris. f) Weep holes may be drilled into the side of the inlet. g) Protect weep holes with wire mesh and washed aggregate. h) Weep holes must be sealed when removing and stabilizing excavated area. i) A temporary dike may be necessary on the down slope side of the structure to prevent bypass flow. Maintenance Standards 1. Any accumulated sediment on or around inlet protection shall be removed immediately. Sediment shall not be removed with water, and all sediment must be disposed of as fill on site or hauled off site. 2. Any sediment in the catch basin insert shall be removed when the sediment has filled one-third of the available storage. The filter media for the insert shall be cleaned or replaced at least monthly. 3. Regular maintenance is critical for all forms of catch basin/inlet protection. Unlike many forms of protection that fail gradually, catch basin protection will fail suddenly and completely if not maintained properly. 2016 Surface Water Design Manual – Appendix D 4/24/2016 D-55 SECTION D.2.1 ESC MEASURES FIGURE D.2.1.5.E FILTER FABRIC PROTECTION FIGURE D.2.1.5.F CATCH BASIN INSERT CATCH BASIN NOTE: ONLY TO BE USED WHERE PONDING OF WATER ABOVE THE CATCH BASIN WILL NOT CAUSE TRAFFIC PROBLEMS AND WHERE OVERFLOW WILL NOT RESULT IN EROSION OF SLOPES. GRATE STANDARD STRENGTH FILTER FABRIC NOTE: THIS DETAIL IS ONLY SCHEMATIC. ANY INSERT IS ALLOWED THAT HAS: •A MIN. 0.5 C.F. OF STORAGE, •THE MEANS TO DEWATER THE STORED SEDIMENT, •AN OVERFLOW, AND •CAN BE EASILY MAINTAINED. OVERFLOW GRATECATCH BASIN POROUS BOTTOM SOLID WALLS FILTER MEDIA FOR DEWATERING 4/24/2016 2016 Surface Water Design Manual – Appendix D D-56 D.2.1.5 SEDIMENT RETENTION FIGURE D.2.1.5.G BLOCK AND GRAVEL CURB INLET PROTECTION 1.USE BLOCK AND GRAVEL TYPE SEDIMENT BARRIER WHEN CURB INLET IS LOCATED IN GENTLY SLOPING SEGMENT, WHERE WATER CAN POND AND ALLOW SEDIMENT TO SEPARATE FROM RUNOFF. 2.BARRIER SHALL ALLOW FOR OVERFLOW FROM SEVERE STORM EVENT. 3.INSPECT BARRIERS AND REMOVE SEDIMENT AFTER EACH STORM EVENT. SEDIMENT AND GRAVEL MUST BE REMOVED FROM THE TRAVELED WAY IMMEDIATELY. 2x4 WOOD STUD OVERFLOW WATER A A PLAN VIEW NTS SECTION A-A NTS BLOCK AND GRAVEL CURB INLET PROTECTION NTS CATCH BASIN COVER CURB INLET CONCRETE BLOCKS CATCH BASIN COVER CURB INLET CATCH BASIN BACK OF SIDEWALK CURB FACE 3/4" DRAIN GRAVEL (20 mm) WIRE SCREEN OR FILTER FABRIC POND HEIGHT WIRE SCREEN OR FILTER FABRIC 2x4 WOOD STUD (100x50 TIMBER STUD) 3/4" DRAIN GRAVEL (20 mm) NOTES: 2016 Surface Water Design Manual – Appendix D 4/24/2016 D-57 SECTION D.2.1 ESC MEASURES FIGURE D.2.1.5.H CURB AND GUTTER BARRIER PROTECTION RUNOFF RUNOFF SPILLWAY 1.PLACE CURB-TYPE SEDIMENT BARRIERS ON GENTLY SLOPING STREET SEGMENTS, WHERE WATER CAN POND AND ALLOW SEDIMENT TO SEPARATE FROM RUNOFF. 2.SANDBAGS OF EITHER BURLAP OR WOVEN GEOTEXTILE FABRIC ARE FILLED WITH GRAVEL, LAYERED AND PACKED TIGHTLY. 3.LEAVE A ONE-SANDBAG GAP IN THE TOP ROW TO PROVIDE A SPILLWAY FOR OVERFLOW. 4.INSPECT BARRIERS AND REMOVE SEDIMENT AFTER EACH STORM EVENT. SEDIMENT AND GRAVEL MUST BE REMOVED FROM THE TRAVELED WAY IMMEDIATELY. GRAVEL FILLED SANDBAGS STACKED TIGHTLY DRAIN GRATE GUTTER CURB FACE CURB INLET SANDBAGS TO OVERLAP ONTO CURB BACK OF SIDEWALK PLAN VIEW NTS CURB AND GUTTER BARRIER NTS NOTES: 4/24/2016 2016 Surface Water Design Manual – Appendix D D-58 D.2.1.8 DUST CONTROL D.2.1.8 DUST CONTROL Preventative measures to minimize the wind transport of soil shall be taken when a traffic hazard may be created or when sediment transported by wind is likely to be deposited in water resources or adjacent properties. Purpose: To prevent wind transport of dust from exposed soil surfaces onto roadways, drainage ways, and surface waters. When to Install: Dust control shall be implemented when exposed soils are dry to the point that wind transport is possible and roadways, drainage ways, or surface waters are likely to be impacted. Dust control measures may consist of chemical, structural, or mechanical methods. Measures to Install: Water is the most common dust control (or palliative) used in the area. When using water for dust control, the exposed soils shall be sprayed until wet, but runoff shall not be generated by spraying. Calcium chloride, Magnesium chloride, Lignin derivatives, Tree Resin Emulsions, and Synthetic Polymer Emulsions may also be used for dust control. Exposed areas shall be re-sprayed as needed. Oil shall not be used for dust control. The following table lists many common dust control measures. Some of the measures are not recommended for use in King County and must have prior approval prior to use from the DPER inspector assigned to specific projects. 2016 Surface Water Design Manual – Appendix D 4/24/2016 D-69 SECTION D.2.1 ESC MEASURES TABLE D.2.1.8.A DUST CONTROL MEASURES METHOD CONSIDERATIONS SITE PREPARATION RECOMMENDED APPLICATION RATE Water -Most commonly used practice -Evaporates quickly -Lasts less than 1 day For all liquid agents: -Blade a small surface -Crown or slope surface to avoid ponding -Compact soils if needed -Uniformly pre-wet at 0.03 – 0.3 gal/sq yd -Apply solution under pressure. Overlap solution 6 – 12 inches -Allow treated area to cure 0 – 4 hours -Compact area after curing -Apply second treatment before first treatment becomes ineffective 0.125 gal/sq yd every 20 to 30 minutes Salts Calcium Chloride (CaCl) -Restricts evaporation -Lasts 6-12 months -Can be corrosive -Less effective in low humidity -Can build up in soils and leach by rain Apply 38% solution at 1.21L/m2 (0.27 gal/yd2) or as loose dry granules per manufacturer Magnesium Chloride (MgCl) -Restricts evaporation -Works at higher temperatures and lower humidity than CaCl -May be more costly than CaCl Apply 26 – 32% solution at 2.3 L/m2 (0.5 gal/yd2) Sodium Chloride (NaCl) -Effective over smaller range of conditions -Less expensive -Can be corrosive -Less effective in low humidity Per Manufacturer Silicates -Generally expensive -Available in small quantities -Require Second application Surfactants -High evaporation rates -Effective for short time periods -Must apply frequently Copolymers -Forms semi-permeable transparent crust -Resists ultraviolet radiation and moisture induced breakdown -Last 1 to 2 years 750 – 940 L/ha (80 – 100 gal/ac) Petroleum Products -Used oil is prohibited as a dust control method -Bind soil particles -May hinder foliage growth -Environmental and aesthetic concerns -Higher cost Use 57 – 63% resins as base. Apply at 750 – 940 L/ha (80-100 gal/ac) Lignin Sulfonate -Paper industry waste product -Acts as dispersing agent -Best in dry climates -Can be slippery -Will decrease Dissolved Oxygen in waterways therefore cannot be used adjacent to surface water systems Loosen surface 25-50 mm (1 – 2 inches) Need 4-8% fines Vegetable Oils -Coat grains of soils, so limited binding ability -May become brittle -Limited availability Per Manufacturer Spray on Adhesives -Available as organic or synthetic -Effective on dry, hard soils -Forms a crust -Can last 3 to 4 years Per Manufacturer 4/24/2016 2016 Surface Water Design Manual – Appendix D D-70 P a g e | 31 C. Correspondence P a g e | 32 D. Site Inspection Form Project Name Permit # Inspection Date Time Name of Certified Erosion Sediment Control Lead (CESCL) or qualified inspector if less than one acre Print Name: Approximate rainfall amount since the last inspection (in inches): Approximate rainfall amount in the last 24 hours (in inches): Current Weather Clear Cloudy Mist Rain Wind Fog A. Type of inspection: Weekly Post Storm Event Other B. Phase of Active Construction (check all that apply): Pre Construction/installation of erosion/sediment controls Clearing/Demo/Grading Infrastructure/storm/roads Concrete pours Vertical Construction/buildings Utilities Offsite improvements Site temporary stabilized Final stabilization C. Questions: 1. Were all areas of construction and discharge points inspected? Yes No 2. Did you observe the presence of suspended sediment, turbidity, discoloration, or oil sheen Yes No 3. Was a water quality sample taken during inspection? (refer to permit conditions S4 & S5) Yes No 4. Was there a turbid discharge 250 NTU or greater, or Transparency 6 cm or less?* Yes No 5. If yes to #4 was it reported to Ecology? Yes No 6. Is pH sampling required? pH range required is 6.5 to 8.5. Yes No If answering yes to a discharge, describe the event. Include when, where, and why it happened; what action was taken, and when. *If answering yes to # 4 record NTU/Transparency with continual sampling daily until turbidity is 25 NTU or less/ transparenc y is 33 cm or greater. Sampling Results: Date: Parameter Method (circle one) Result Other/Note NTU cm pH Turbidity tube, meter, laboratory pH Paper, kit, meter P a g e | 33 D. Check the observed status of all items. Provide “Action Required “details and dates. Element # Inspection BMPs Inspected BMP needs maintenance BMP failed Action required (describe in section F) yes no n/a 1 Clearing Limits Before beginning land disturbing activities are all clearing limits, natural resource areas (streams, wetlands, buffers, trees) protected with barriers or similar BMPs? (high visibility recommended) 2 Construction Access Construction access is stabilized with quarry spalls or equivalent BMP to prevent sediment from being tracked onto roads? Sediment tracked onto the road way was cleaned thoroughly at the end of the day or more frequent as necessary. 3 Control Flow Rates Are flow control measures installed to control stormwater volumes and velocity during construction and do they protect downstream properties and waterways from erosion? If permanent infiltration ponds are used for flow control during construction, are they protected from siltation? 4 Sediment Controls All perimeter sediment controls (e.g. silt fence, wattles, compost socks, berms, etc.) installed, and maintained in accordance with the Stormwater Pollution Prevention Plan (SWPPP). Sediment control BMPs (sediment ponds, traps, filters etc.) have been constructed and functional as the first step of grading. Stormwater runoff from disturbed areas is directed to sediment removal BMP. 5 Stabilize Soils Have exposed un-worked soils been stabilized with effective BMP to prevent erosion and sediment deposition? P a g e | 34 Element # Inspection BMPs Inspected BMP needs maintenance BMP failed Action required (describe in section F) yes no n/a 5 Stabilize Soils Cont. Are stockpiles stabilized from erosion, protected with sediment trapping measures and located away from drain inlet, waterways, and drainage channels? Have soils been stabilized at the end of the shift, before a holiday or weekend if needed based on the weather forecast? 6 Protect Slopes Has stormwater and ground water been diverted away from slopes and disturbed areas with interceptor dikes, pipes and or swales? Is off-site storm water managed separately from stormwater generated on the site? Is excavated material placed on uphill side of trenches consistent with safety and space considerations? Have check dams been placed at regular intervals within constructed channels that are cut down a slope? 7 Drain Inlets Storm drain inlets made operable during construction are protected. Are existing storm drains within the influence of the project protected? 8 Stabilize Channel and Outlets Have all on-site conveyance channels been designed, constructed and stabilized to prevent erosion from expected peak flows? Is stabilization, including armoring material, adequate to prevent erosion of outlets, adjacent stream banks, slopes and downstream conveyance systems? 9 Control Pollutants Are waste materials and demolition debris handled and disposed of to prevent contamination of stormwater? Has cover been provided for all chemicals, liquid products, petroleum products, and other material? Has secondary containment been provided capable of containing 110% of the volume? Were contaminated surfaces cleaned immediately after a spill incident? Were BMPs used to prevent contamination of stormwater by a pH modifying sources? P a g e | 35 Element # Inspection BMPs Inspected BMP needs maintenance BMP failed Action required (describe in section F) yes no n/a 9 Cont. Wheel wash wastewater is handled and disposed of properly. 10 Control Dewatering Concrete washout in designated areas. No washout or excess concrete on the ground. Dewatering has been done to an approved source and in compliance with the SWPPP. Were there any clean non turbid dewatering discharges? 11 Maintain BMP Are all temporary and permanent erosion and sediment control BMPs maintained to perform as intended? 12 Manage the Project Has the project been phased to the maximum degree practicable? Has regular inspection, monitoring and maintenance been performed as required by the permit? Has the SWPPP been updated, implemented and records maintained? 13 Protect LID Is all Bioretention and Rain Garden Facilities protected from sedimentation with appropriate BMPs? Is the Bioretention and Rain Garden protected against over compaction of construction equipment and foot traffic to retain its infiltration capabilities? Permeable pavements are clean and free of sediment and sediment laden- water runoff. Muddy construction equipment has not been on the base material or pavement. Have soiled permeable pavements been cleaned of sediments and pass infiltration test as required by stormwater manual methodology? Heavy equipment has been kept off existing soils under LID facilities to retain infiltration rate. E. Check all areas that have been inspected. All in place BMPs All disturbed soils All concrete wash out area All material storage areas All discharge locations All equipment storage areas All construction entrances/exits P a g e | 36 F. Elements checked “Action Required” (section D) describe corrective action to be taken. List the element number; be specific on location and work needed. Document, initial, and date when the corrective action has been completed and inspected. Element # Description and Location Action Required Completion Date Initials Attach additional page if needed Sign the following certification: “I certify that this report is true, accurate, and complete, to the best of my knowledge and belief” Inspected by: (print) (Signature) Date: Title/Qualification of Inspector: P a g e | 37 E. Construction Stormwater General Permit (CSWGP) P a g e | 38 F. 303(d) List Waterbodies / TMDL Waterbodies Information Listing ID: 12193 Main Listing Information Listing ID: 12193 2014 Category: 5 Waterbody Name: WASHINGTON LAKE 2012 Category: 5 Medium: Water 2008 Category: 5 Parameter: Bacteria 2004 Category: 5 WQI Project: None Assigned On 1998 303(d) List?: Y Designated Use: None Assigned On 1996 303(d) List?: N Assessment Unit Assessment Unit ID: 47122F2A0 Location Identification Counties: King Waterbody ID (WBID): WA-08-9350 Town/Range/Section (Legacy): None Assigned WRIA: 8 - Cedar-Sammamish Waterbody Class: LAK Basis King County unpublished data from station 0828SB show a geometric mean of 220 cfu/100mL with 53% exceeding the percentile criterion during 1998. King County unpublished data from station 0828SB show a geometric mean of 82 cfu/100mL with 35% exceeding the percentile criterion during 1999. King County unpublished data from station 0828SB show a geometric mean of 94 cfu/100mL with 56% exceeding the percentile criterion during 2000. King County unpublished data from station 0828SB show a geometric mean of 31 cfu/100mL with 20% exceeding the percentile criterion during 2001. King County unpublished data from station 0828SB show a geometric mean of 105 cfu/100mL with 50% exceeding the percentile criterion during 2002. Remarks No Remarks Entered EIM No EIM Records Entered Page 1 of 1Print Approved Listing 5/22/2019https://apps.ecology.wa.gov/approvedwqa/ApprovedPrintListing.aspx?LISTING_ID=12193 Listing ID: 52853 Main Listing Information Listing ID: 52853 2014 Category: 5 Waterbody Name: WASHINGTON LAKE 2012 Category: 5 Medium: Water 2008 Category: 5 Parameter: Total Phosphorus 2004 Category: 3 WQI Project: None Assigned On 1998 303(d) List?: N Designated Use: None Assigned On 1996 303(d) List?: N Assessment Unit Assessment Unit ID: 47122H2E6 Location Identification Counties: King Waterbody ID (WBID): None Assigned Town/Range/Section (Legacy): None Assigned WRIA: 8 - Cedar-Sammamish Waterbody Class: LAK Basis Location ID [KCM-0804] -- In 2004 the summer epilimnetic mean concentration of total phosphorus samples did not exceed the action value for this ecoregion (20 ug/L). Location ID [KCM-0804] -- In 2005 the summer epilimnetic mean concentration of total phosphorus samples did not exceed the action value for this ecoregion (20 ug/L). Location ID [KCM-0804] -- In 2006 the summer epilimnetic mean concentration of total phosphorus samples exceeded the action value for this ecoregion (20 ug/L). Remarks No Remarks Entered EIM User Study ID:User Location ID: KClake-1 KCM-0804 KClake-1 KCM-0804 Page 1 of 1Print Approved Listing 5/22/2019https://apps.ecology.wa.gov/approvedwqa/ApprovedPrintListing.aspx?LISTING_ID=52853 P a g e | 39 G. Contaminated Site Information P a g e | 40 H. Engineering Calculations Appendix B WWHM Report WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: Apron E - Flow Rate Site Name: Site Address: City : Report Date: 6/13/2019 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2018/10/10 Version : 4.2.16 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : On-site Basin Bypass: No GroundWater: No Pervious Land Use acre C, Lawn, Flat 1 Pervious Total 1 Impervious Land Use acre ROADS FLAT 8.85 ROOF TOPS FLAT 0.28 Impervious Total 9.13 Basin Total 10.13 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : On-site Basin Bypass: No GroundWater: No Pervious Land Use acre C, Lawn, Flat .89 Pervious Total 0.89 Impervious Land Use acre ROADS FLAT 7.4 ROOF TOPS FLAT 1.84 Impervious Total 9.24 Basin Total 10.13 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ ANALYSIS RESULTS ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:1 Total Impervious Area:9.13 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0.89 Total Impervious Area:9.24 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 3.545198 5 year 4.499727 10 year 5.150686 25 year 5.997548 50 year 6.64738 100 year 7.314334 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 3.580111 5 year 4.541324 10 year 5.196539 25 year 6.04863 50 year 6.702267 100 year 7.37296 ___________________________________________________________________ WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: Boeing Apron E WQ Treatment - North Site Name: Boeing Apron E Site Address: City : Renton Report Date: 6/13/2019 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2017/04/14 Version : 4.2.13 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Flat 3.43 Pervious Total 3.43 Impervious Land Use acre Impervious Total 0 Basin Total 3.43 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre Pervious Total 0 Impervious Land Use acre PARKING FLAT 3.43 Impervious Total 3.43 Basin Total 3.43 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:3.43 Total Impervious Area:0 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0 Total Impervious Area:3.43 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.100845 5 year 0.158381 10 year 0.190987 25 year 0.225531 50 year 0.246907 100 year 0.265088 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 1.307737 5 year 1.651824 10 year 1.885607 25 year 2.188858 50 year 2.420958 100 year 2.658694 ___________________________________________________________________ ___________________________________________________________________ Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0.4218 acre-feet On-line facility target flow: 0.557 cfs. Adjusted for 15 min: 0.557 cfs. Off-line facility target flow: 0.3148 cfs. = 141.3 gpm Adjusted for 15 min: 0.3148 cfs. ___________________________________________________________________ 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. 2005-2019; All Rights Reserved. WWHM2012 PROJECT REPORT ___________________________________________________________________ Project Name: Boeing Apron E WQ Treatment - South Site Name: Boeing Apron E Site Address: City : Renton Report Date: 6/13/2019 Gage : Seatac Data Start : 1948/10/01 Data End : 2009/09/30 Precip Scale: 1.00 Version Date: 2017/04/14 Version : 4.2.13 ___________________________________________________________________ Low Flow Threshold for POC 1 : 50 Percent of the 2 Year ___________________________________________________________________ High Flow Threshold for POC 1: 50 year ___________________________________________________________________ PREDEVELOPED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre C, Forest, Flat 4.33 Pervious Total 4.33 Impervious Land Use acre Impervious Total 0 Basin Total 4.33 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ MITIGATED LAND USE Name : Basin 1 Bypass: No GroundWater: No Pervious Land Use acre Pervious Total 0 Impervious Land Use acre PARKING FLAT 4.33 Impervious Total 4.33 Basin Total 4.33 ___________________________________________________________________ Element Flows To: Surface Interflow Groundwater ___________________________________________________________________ ___________________________________________________________________ ANALYSIS RESULTS Stream Protection Duration ___________________________________________________________________ Predeveloped Landuse Totals for POC #1 Total Pervious Area:4.33 Total Impervious Area:0 ___________________________________________________________________ Mitigated Landuse Totals for POC #1 Total Pervious Area:0 Total Impervious Area:4.33 ___________________________________________________________________ Flow Frequency Return Periods for Predeveloped. POC #1 Return Period Flow(cfs) 2 year 0.127306 5 year 0.199938 10 year 0.241101 25 year 0.284708 50 year 0.311693 100 year 0.334645 Flow Frequency Return Periods for Mitigated. POC #1 Return Period Flow(cfs) 2 year 1.650876 5 year 2.085247 10 year 2.380373 25 year 2.763193 50 year 3.056193 100 year 3.356309 ___________________________________________________________________ ___________________________________________________________________ Water Quality BMP Flow and Volume for POC #1 On-line facility volume: 0.5325 acre-feet On-line facility target flow: 0.7032 cfs. Adjusted for 15 min: 0.7032 cfs. Off-line facility target flow: 0.3975 cfs. = 178.4 gpm Adjusted for 15 min: 0.3975 cfs. ___________________________________________________________________ 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. 2005-2019; All Rights Reserved. Appendix C Water Quality Treatment Standard Detail STANDARD DETAIL STORMWATER BIOFILTRATION SYSTEM MWS-L-8-12-V PLAN VIEW ELEVATION VIEW RIGHT END VIEW LEFT END VIEW GENERAL NOTES INSTALLATION NOTES SITE SPECIFIC DATA STANDARD DETAIL STORMWATER BIOFILTRATION SYSTEM MWS-L-8-16-V PLAN VIEW ELEVATION VIEW RIGHT END VIEW LEFT END VIEW GENERAL NOTES INSTALLATION NOTES SITE SPECIFIC DATA