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L., <br />1 <br />I <br />1 <br />I <br />1 <br />1 <br />I <br />I <br />1 <br />to <br />11 <br />1 <br />H <br />Page 10 of 29 <br />IV. Analysis and Design of Required Runoff Control <br />Runoff Control: <br />Runoff control is not required for this site because it is a redevelopment project. <br />Water Quality: <br />Water quality mitigation is required for this project. Water quality mitigation will be <br />achieved by the use of a storm filter canister system (Stormfilter°J by Contech Stormwater <br />Solutions, Portland OR). Pretreatment is required with this water quality option. The <br />pretreatment option selected for use with the Stormfilter�o vault is the Aqua -Swirls' by <br />AquaShield, Chattanooga, TN. A (low splitterer will take the pretreatment and water <br />quality facilities offline, hydraulically, when the water quality design storm is exceeded. <br />The Western Washington Hydrology Model, version 2 (WWHM2) continuous modeling <br />program provided by the D.O.G. was used to determine the targeted water quality flow <br />rate for the Stormfilter, the Aqua -swirl and the flow splitter. The total paved and grass <br />areas conveyed from the site were measured. The areas are: <br />DEVELOPED CONDITIONS* <br />Total Area = 4.04 AC <br />GROUND COVER <br />AREA (acre) <br />Till-GraEs (Landscaping) <br />2.24 <br />Impervious <br />1.80 <br />* u.92 AU of clean building rooftops not conveyed for WQ <br />Using the W WMH2 program with the areas above, the developed runoff from the site <br />will be: <br />Flow Frequency <br />Return Periods for Developed Mitigated <br />Return Period <br />Flow(cfs) <br />2 year <br />0.650203 <br />5 year <br />0.935714 <br />10 year <br />1.145537 <br />125 year <br />1.434644 <br />year <br />1.667723 <br />1150 <br />100 year <br />1.916248 <br />