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U KLEINFELDER r (NO3) and 10 mg/1 as Nitrogen (N) in groundwater. In our evaluation of nitrate loading,we have used the Hantzsche mass balance equation (source: Predicting Ground-Water Nitrate-Nitrogen Impacts, Hantzsche and Finnemore (1992)), which is presented below with an explanation for each factor and the value used in our study. The selection of parameters was based on previous y studies and investigations performed by our firm and others, San Joaquin County Sewage Standards, communications with Mr. Mike Huggins at SJCPHS/EHD, and information provided in a report dated March 19, 1997 prepared by the Questa Engineering Corporation and authored ` by Mr. Hantzsche for a development in the Stockton area. Ne=AWNw_ (1-D) +(Nb) R ` AW+R Where: �- Ne = Average calculated nitrate-nitrogen in groundwater resulting from domestic sources and precipitation—mg/l, as N A = Number of dwelling units per acre on septic tanks (unit/acre) = 0.418 (estimated based on an estimated water usage of 1700 gal./day, a typical water usage for 50 employees at 30 gal/employee plus 20 visitors at 10 gal./visitor (per the SJC PHS/EHD Sewage Standards) divided by 150 gal./day to obtain an equivalent number of homes, divided by 27.12 acres) W = Annual wastewater loading per dwelling unit per acre(inches) =2.0 inches (per year per dwelling unit assuming a flow of 150 gal./day/dwelling unit) Nw = Nitrate concentration of nitrified leachfield effluent (mg/1) = 70 mg/l typical (based on communication with Mr. Mike Huggins with SJCPH/EHD) ` D = Percent dentrification of leachfield effluent = 0.25 percent (0.1 to 0.35 percent typical per Hantzsche and Finnemore ([1992]). R = Annual deep percolation of precipitation (inches) = 9.6 inches (representing 80 percent of average annual rainfall of 12 inches in project area. Remaining 20 percent of rainfall is assumed to drain off-site into natural or manmade drainages) Nb = Background nitrate nitrogen concentration of rainfall recharge at the water table = 0.5 mg/1 (per Technical Memorandum, Hydrologic and Soil Investigation for the Chico Urban Area,page 6, Dames and Moore, April 1996) I Our calculation is as follows: Ne = 0.418(2)(70)(1 —0.25)+0.5(9.6) = 43.9+4.8 = 4.7 mg/l as N L 0.418(2)+9.6 0.836 +9.6 L 13257.G01/ST02R023 September 18,2002 ©2002 Kleinfelder,Inc. Page 3 of 4