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Drainage Report—Revision 1 <br /> Boeing Everett—Rail Spur Parking Lot September 26,2013 <br /> preceded by detention facilities. For those water quality facilities preceded by detention facilities, <br /> the design storm is the full 2-year discharge from the detention facility. The 2-year flow rates for <br /> each basin, along with the associated water quality flow rate are shown in TABLE 2 below. <br /> TABLE 2 StormShed Water Quality Treatment Flow Rates <br /> PGIS Area 2 Year Flow *WQ Flow <br /> Basin (acres) Rate(cfs) Rate(cfs) <br /> North 1.85 0.6454 0.4131 <br /> South 0.28 ; 0.0975 0.0624 <br /> *The north and south basin are required to treat 64%of the 2-year, <br /> 24-hour storm. <br /> Runoff from the north basin will flow to a Contech Stormfilter Peak Diversion Vault. The 8'x11' <br /> vault holds(17) 27"tall Stormfilter cartridges. The size of the facility was based on the treatment <br /> capacity of the cartridges. The 27"tall cartridges were selected because they can treat the highest <br /> flow rate per cartridge, resulting in the smallest system with the lowest installed cost. The south <br /> sub-basin flow will be treated through the use of a 4-cartridge Contech Steel Catch Basin with <br /> 18"tall cartridges requiring 2.3' of hydraulic drop through the structure. <br /> TABLE 3 below shows the sub-basin, the selected cartridge type and associated allowable flow <br /> rate, the design flow and the resultant number of cartridges required. <br /> TABLE 3 Water Quality Facilities Sizing Summary <br /> Allowable ' <br /> Flow <br /> Cartridge Rate/Cartridge Design Flow #of <br /> Basin Type (gpm) (gpm) Cartridges Facility Type <br /> 8'x11' Peak Diversion <br /> StormFilter Vault (17 <br /> North 27"Tall 11.25 185.39 17 cartridges) <br /> Catch Basin - Cartridge <br /> South 18" Tall 7.50 28.01 4.00 Unit <br /> 5.4 Proposed Facilities Summary <br /> Proposed drainage facilities include catch basins and water quality facilities. Runoff from the <br /> north subbasin will enter catch basins on the north side of the proposed pavement area before <br /> conveyance to an 8'x11' StormFilter Vault and discharge to Japanese Gulch. Runoff from the <br /> central subbasin will enter catch basins (fitted with spill control) within the proposed pavement <br /> area before conveyance to an existing water quality swale. Runoff from the central subbasin will <br /> flow through three swales before reaching an existing detention pond to the west of Perimeter <br /> DCG, Inc. Page 7 of 11 <br />