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KLEINFELDER <br /> used the Hantzsche mass balance equation (source: Predicting Ground-Water Nitrate-Nitrogen <br /> Impacts, Hantzsche and Finnemore (1992)), which is presented below with an explanation for <br /> each factor and the value used in our study. The selection of parameters was based on previous <br /> studies and investigations performed by our firm and others, San Joaquin County Sewage <br /> Standards, communications with Mr. Mike Huggins with the SJCPHS/EHD, and information <br /> provided in a report dated March 19, 1997 prepared by the Questa Engineering Corporation and <br /> authored by Mr. Hantzsche for a development in the Stockton area. <br /> Ne =AWNw (1-D) + R <br /> AW+R <br /> Where: <br /> N, = Average calculated nitrate-nitrogen in groundwater resulting from domestic sources <br /> and precipitation—mg/l, as N <br /> A = Number of dwelling units per acre on septic tanks (unit/acre) = 1.246 (estimated <br /> based on an estimated water usage of 2990 gal./day, a typical water use for 299 <br /> people at a church facility at 10 gallons/seat per the SJCPHS/EHD Sewage <br /> tan azdS divided by 150 gal./day to obtain an equivalent number of homes, divided <br /> by 16.0 acres) <br /> W = Annual wastewater loading per dwelling unit per acre (inches) =2.0 inches (per year <br /> per dwelling unit assuming a flow of 150 gal./day/dwelling unit) <br /> NW, = Nitrate concentration of nitrified leachfield effluent (mg/1) = 70 mg/1 typical <br /> (communication with Mr. Mike Huggins with SHCPHS/EHD) <br /> D = Percent dentrification of leachfield effluent = 0.25 percent (0.1 to 0.35 percent <br /> typical per Hantzsche and Finnemore ([1992]). <br /> R = Annual deep percolation of precipitation (inches) = 11.9 inches (representing 85 <br /> percent of average annual rainfall of 14 inches in project area. Remaining 15 <br /> percent of rainfall is assumed to drain off-site into natural or manmade drainages) <br /> Nb = Background nitrate nitrogen concentration of rainfall recharge at the water table = <br /> 0.5 mg/l (per Technical Memorandum, Hydrologic and Soil Investigation for the <br /> Chico Urban Area, page 6, Dames and Moore, April 1996) <br /> Our calculation is as follows: <br /> N, = 1.246(2)(70)(1 —0.25) +0.5(11.9) = 130.83 + 5.95 (:9.51mg/lasN <br /> 1.246(2)+11.9 2.492 +11.9 <br /> 17357.GO1/ST02R327 August 8,2002 <br /> 0 2002 Kleinfelder,Inc. Page 4 of 5 <br />