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KLEINFELDER <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) = 0.891 (estimated <br /> based on an estimated average water usage of 2,139 gal./day, a typical water usage <br /> for 499 people at a church facility utilized 3 days per week divided by 7 days per <br /> week at 10 gallons/seat per the SJCEHD Sewage Standards, divided by 150 gal./day <br /> to obtain an equivalent number of homes, divided 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/I typical <br /> (communication with Mr. Mike Huggins with SJCEHD) <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/1 (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 /> Ne = 0.891(2)(70)(1 —0.25) +0.5(11.9) = 93.555 + 5.95 = 7.3 mg/1 as N <br /> 0.891(2)+11.9 1.782 +11.9 <br /> CONCLUSIONS <br /> Based on the above evaluation, we conclude that wastewater produced by the proposed leach <br /> field should not have a nitrate as nitrogen(N) concentration at the groundwater level greater than <br /> 10 mg/l. The results of our percolation tests indicate that a conventional septic tank/leach trench <br /> sewage disposal system with seepage pits should adequately serve the proposed development. <br /> The seepage pits should extend to the sandy soils underlying the site that were encountered at a <br /> depth ranging of about 10-%z feet below site grade. <br /> 17357.G01/ST02R730 November 5,2002 <br /> ©2002 Kleinfelder,Inc. Page 2 of 3 <br />