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r. Wastewater Treatment System 1%0,W -+0l' FALL CREEK `�- Engineering Report ENGINEERING,INC. To confirm the treatment efficiency, FCE calculated the expected removal efficiency for the proposed wetland. A first order equation was used to model pollution removal, assuming that the peak wetland influent BOD is 4,000 mg/L (20% of 5,000 mg/L BOD removed in the septic .. tank), t is assumed to be 10 days, and KT is 0.69 d-1. Therefore the effluent BOD concentration is: C, = C e-"" = 4000e-(0.69.10) = 4mg/L . This shows that a 10-day detention time will theoretically produce a BOD reduction of over 99%. 4.5. Stormwater Storage Capacity %W The wetland has been designed with a one foot berm around the entire perimeter. The inlet will be gravity flow from the septic tank. And the effluent will be to a pump basin. The wetland will also have an overflow on the outlet side to an existing stormwater detention area. The wetland will have a freeboard volume of approximately 48,000 gallons and the invert of the overflow will be set 8.0" above the top of the wetland. The existing stormwater detention area will be reshaped to provide and additional 71,000 gallons of storage. The system will provide a total stormwater storage volume of 119,000 gallons. `" To determine whether this freeboard would be adequate to contain rainfall and stormwater runoff %W from the 100-year, 24-hour storm, a simple water balance was performed. According to %W NOAA's Precipitation-Frequency Atlas of California, the depth of water in the 100-Yr 24-hr storm is 3.8 inches. This number was used to calculate the stormwater runoff at the winery %W facility. �- V, = A*d*C, = 56,000sf*3.8in*(lz n)*0.88 = 15,600cf = 116,700gallons. This calculation shows that the 100-year, 24-hour storm (116,700 gallons) would be contained by the stormwater facilities (119,000 gallons). v ,%W %W JESSIE'S GROVE WINERY MAY 2002 �- 19