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k KL FINFELDER <br /> r <br /> A = Number of dwelling units per acre on septic tanks (unit/acre) = 0.214 (estimated <br /> based on an estimated water usage of 150 gal./day, a typical water usage fora single <br /> family residence per the SJC PHS/EHD Sewage Standards divided by 150 gal./day <br /> to obtain an equivalent number of homes, divided by 4.68 acres) <br /> W = Annual wastewater loading per dwelling unit per acre (inches) =2.0 inches (per year <br /> li per dwelling unit assuming a flow of 150 gal./day/dwelling unit) <br /> N, = Nitrate concentration of nitrified leachf eld effluent (mg/1) = 35 mg/1 typical <br /> (Hantzsche and Finnemore (1992)) <br /> D = Percent dentrif cation 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) = 1.9 inches (representing 20 <br /> percent of average annual rainfall of 9.5 inches in project area. Remaining 80 <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 /> N, = 0.214(2)(35)(l.—0.25 +0.5(1.9) = 11.2 + 095 = 5.23 mg/1 as N <br /> 0.2142)+1.9 0.43 +1.9 <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. Due to the shallow depth at which groundwater was encountered,�we�,understand-that-a <br /> mounded-type septic system will be required by SJC PHS/EHD: <br /> LIMITATIONS <br /> The conclusions of this report are based on the information provided regarding the existing and <br /> proposed development and on the site conditions. It was assumed that the percolation test results <br /> are representative of the subsurface conditions in the general area. <br /> 16797.G01/ST02R 170 July 1,2002 <br /> ©2002 Kleinfelder,Inc. Page 3 of 4 <br />