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Memorandum Date: July, 2014 From: Bruce J. Friedhoff To: Sangeeta Lewis RE: Forward,Inc. Compost Facility Stormwater Improvements PROJECT UNDERSTANDING Item H.8.H of Forward's recently adopted Waste Discharge Requirements(WDRs)R5-2014-0006 requires the submittal of a report by February 1,2015 that demonstrates that the compost area meets or exceeds the relevant facility specifications. The purpose of this memorandum is to document the surface water design for the Compost Facility run-on and run-off controls for the following requirements: 1. Compost Facility shall implement storm water BMPs so that run-off water does not adversely affect the beneficial uses of any downstream water body; 2. The Discharger shall monitor leachate and water in the retention basin as required by MRP R5-2014-0006 3. The retention basin shall be equipped with a synthetic liner, shall maintain a minimum two feet of freeboard and shall be designed and operated to minimize the downward percolation of constituents; 4. The Compost and Compost storage pads shall be designed,constructed and maintained to prevent to the greatest extent possible,ponding, infiltration, inundation, erosion, slope failure, and washout; 5. The pad or pads shall have a minimum one percent slope; 6. The Discharger shall maintain an effective run-on control system and for the composting area a run-off control system designed to withstand the maximum peak flow from a 25-year, 10- minute storm;and 7. The retention basin shall be designed to accommodate all runoff and direct precipitation from a 25-year, 24-hour storm and maintain two feet of freeboard. WATER BUDGET Monthly and annual precipitation data was downloaded from the California Department of Water Resources,Flood&Safety,Climate Data,Precipitation,Monthly Historical Data, for Stockton AP,July 2014 Web Site.Monthly runoff from rainfall was computed using the SCS runoff equation and a Curve Number of 88. Monthly evaporation data was down loaded from the Western Regional Climate Center, July 2014. The monthly composed water demand was assumed to be 18.7 acres times the monthly evaporation depth.The required monthly volume of storage for process water storage was computed by subtracting the monthly runoff by the process water demand(but not less than zero).The difference between demand and supply is assumed to be supplied by other sources.The maximum monthly storage volume is 10.1 Acre Feet and occurs in January.