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a <br /> Goldfinch Brothers <br /> Drainage Study <br /> August 27,2008 <br /> 3. DEVELOPED CONDITIONS <br /> The proposed development will provide for a future building addition onto the existing <br /> on the adjacent Goldfinch property to the west. The building will be an assembly or light <br /> I manufacturing building, which will represent a future expansion of capacity for the <br /> Goldfinch brothers company. The building will be supported by parking, loading docks <br /> and travel lanes. Initially, the parking areas and travel lanes will support the existing <br /> Iproduction operation. <br /> DRAINAGE PROPOSAL <br /> Pervious pavement options for detention and water quality benefits were carefully <br /> I examined by the engineer and rejected by the owner. The development proposal will <br /> include conventional detention in a concrete detention vault for the parking lot runoff. <br /> I The required volume for the future building roof will be included. Water quality will be <br /> provided first by dead storage created in the detention area in excess of the water quality <br /> storm volume. <br /> The runoff from the storage vault will be filtered through storm filter canisters prior to <br /> release into a grassed swale or wetland cell in the buffer area. Roof drains from the future <br /> I building pad will be directed (per City instruction) into the Storage Vault. A Stormwater <br /> overflow from the SEARS detention pond infiltration trench at the NW corner of the site <br /> will be picked up at the property line and by-passed to a level spreader at the edge of the <br /> wetland buffer at the north end of the parking lot development. <br /> Hydrographs for the Project are as follows: <br /> TABLE 1 <br /> PEAK TIME VOLUME <br /> HYD RUNOFF OF OF CONTRIB <br /> NUM RATE PEAK HYDRO AREA • <br /> CFS MIN. CF\ACFT ACRES <br /> I <br /> UNDEVELOPED <br /> 1 0.027 960 1483 CF 1.20 2-YEAR <br /> 2 0.071 550 3342 CF 1.20 10-YEAR <br /> 3 0.163 540 6560 CF 1.20 100-YEAR <br /> I <br /> DEVELOPED <br /> 4 0.331 480 5470 CF 1.20 2-YEAR <br /> 5 0.505 480 8414 CF 1.20 10-YEAR <br /> ie <br /> 6 0.754 480 12677 CF 1.20 100-YEAR <br /> VAULT RELEASE PERFORMANCE <br /> 7 0.015 1470 2148 CF 1.20 2-YEAR <br /> I 8 0.085 980 4715 CF 1.20 10-YEAR <br /> 9 0.156 700 8945 CF 1.20 100-YEAR <br /> I <br /> FULL SITE WATER QUALITY STORMS <br /> 10 0.009 1320 412 CF 1.20 6-Month <br /> 7 0.015 1470 2148 CF 1.20 2-YEAR <br /> ITESC EVENT <br /> 20 0.027 960 1483 CF 1.20 2-YEAR <br /> I <br /> I 5 <br />