3003 W CASINO RD BLDG 40-YD 2019-11-27

Drainage Report—Revision 1 Boeing Everett—Rail Spur Parking Lot September 26,2013 3.1.2 Minimum Requirement#2:Preservation of Natural Drainage Systems The project preserves natural drainage patterns and allows controlled discharges from the north and south subbasins to occur at the natural location to Japanese Gulch to the west of the Boeing campus. Flow control for the new impervious surfaces will be accomplished by use of an existing stormwater detention pond, as shown in the project plans and further detailed in Section 5. 3.1.3 Minimum Requirement#3:Source Control of Pollution Appropriate source control BMPs were selected from Volume IV, Chapter IV-4 of the Stormwater Manual and are discussed in detail in the PSQC Plan. Source control BMPs have been proposed to the maximum extent practicable. 3.1.4 Minimum Requirement#4:Runoff Treatment BMPs Spill-control type oil water separators are required to prevent entry of petroleum-based products into the storm drain system. The project proposes to treat runoff from the central subbasin through the use of an existing 230 feet long and 8 feet wide water quality swale. Runoff from the north subbasin will be treated using an 8'x11' StormFilter vault along the west edge of the proposed pavement area. Runoff from the south basin will be treated in a 4-cartridge StormFilter catch basin. Treatment facilities have been sized to capture more than 90 percent of the annual runoff, per the requirement in Volume I, Chapter 1-2, Section I-2.8 of the Stormwater Manual. Design of the runoff treatment facilities is described in Section 5. 3.1.5 Minimum Requirement#5:Streambank Erosion Control Additional streambank erosion control facilities are not required for this project since runoff from the new and replaced impervious surface will be routed to an existing detention pond to the west of Perimeter Road. See Section 5 for more details on the streambank erosion control exemption. 3.1.6 Minimum Requirement#6: Wetlands Per Volume I, Chapter I-2, Section I-2.10, the wetland requirements do not apply to the project because it does not discharge directly or indirectly through a conveyance system into a wetland. 3.1.7 Minimum Requirement#7: Water Quality Sensitive Areas The project is exempt from Minimum Requirement#7 as the site does not discharge to any water quality sensitive areas. 3.1.8 Minimum Requirement#8: Off-Site Analysis and Mitigation An off-site analysis consistent with Volume I, Chapter I-2, Section I-2.12 of the Stormwater Manual was performed. See Section 4 for a summary of the off-site analysis. 3.1.9 Minimum Requirement#9:Basin Planning There is no known basin plan that would alter and modify the requirements for flow control and water quality treatment from their current design. DCG, Inc. Page 4 of 11