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k`■ KLEINFELDER NITRATE LOADING CALCULATIONS Per SJCEHD requirements, the following summarizes our nitrate loading calculations for the proposed leach fields. The drinking water standard for nitrate is 45 milligrams per liter (NO3) and 10 mg/l as Nitrogen (l) 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. Since there is currently no deed restriction limiting the number of homes on each lot to one, we have calculated the average nitrate (NJ in groundwater based on two homes per lot as required by Mr. Huggins with SJCEHD. The selection of other parameters was based on previous studies by our firm, a report dated March 19, 1997 prepared by the Questa Engineering Corporation and authored by Mr. Hantzsche for a development in the Stockton area, and communications with Mr. Huggins. N.= AWN�(1-D) + (Nbr AW+r Where: Nc = Average calculated nitrate in groundwater resulting from domestic sources and precipitation—mg/l, as N A = Number of dwelling units per acres on septic tanks (unit/acre) = 1.00 (estimated based on 30 homes divided by 30 acres) W = Annual wastewater loading per dwelling unit per acre (inches) = 2.0 inches (based on — 7 150 gpd/residence) e NH, = Nitrate concentration of nitrified leachfield effluent (mg/1) = 35 mg/1 typical (per Mike Huggins) D = Percent denitrification of leachfield effluent = 0.25 percent (0.1 to 0.35 percent typical per Hantzsche and Finnemore (1992). 0.25 selected given the large depth to groundwater and the presence of interbedded low permeable clay layers.) �3 2� r = Annual deep percolation of precipitation (inches) = 9.8 inches (representing 70 percent of the average annual rainfall of 14 inches in project area. Remaining 30 percent of rainfall is assumed to drain off-site into natural or manmade drainages) Nb = Background nitrate concentration of the deep percolating precipitation — mg/1 = 0.5 mg/l (per Technical Memorandum, Hydrologic and Soil Investigation for the Chico Urban Area, page 6, Dames and Moore, April 1996) Our calculations are as follows: C3�\ Ne = 1(2.0)(35)(1—.25)+0.5(9.8) = 52.5 + 4.9 = 4.9 mg/1 as N J 1(2.0) + 9.8 2.0 + 9.8 23197.G01/ST03R289 February 14,2003 0 2003 Kleinfelder,Inc. Page 4 of 5