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I..00 In K L E I NFELDER the standard criteria of 150 gallons per residential unit per day, this corresponds to approximately 24 units on the 12.2-acre facility. 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 studies and investigations performed by our firm and others, San Joaquin County Sewage Standards, communications with Mr. Mike Huggins with the 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. N�=AWNw0-D)+IN- R AW+R Where: N, = 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) = 2.0 (based on an estimated water usage of 3,586 gal./day divided by 150 gal./day to obtain an equivalent number of homes,divided by 12.2 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) = 5 mg/1 (measurement at spray bar was only.3 mg/l which means that waste stream contains very little restroom flow) D = Percent dentrification of leachfield effluent=0.35 percent(0.1 to 0.35 percent typical per Hantzsche and Finnemore([1992]Note that measured total N next to existing line was only .11 mg/I indicating that the near-surface clay soils were very effective in converting nitrate.) R = Annual deep percolation of precipitation (inches) = 10.8 inches (representing 80 percent of average annual rainfall of 13.5 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) Our calculation is as follows: N� = 2(2)(5)(1 —.35)+.5(10.8) = 13 +5.4 = 1.2 mg/1 as N 2(2)+ 10.8 4+10.8 Typically, the value for Nw is assumed to be higher. Very seldom, however, is a septic tank opened and a water sample obtained for actual chemical testing. At Pollardville,the combination 20-0268-01/STO2R886 December 5,2002 ©2002 Kleinfelder,Inc. Page 4 of 5