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03/08/2006 13:33 FAX ?039/041 <br /> KLEINFELDER <br /> A = Number of dwelling units per acres on septic tanks (unittacre) = 1.0 <br /> (estimated based on 15 lots, assuming 2 homes per lot (30 homes total), <br /> divided by 30 acres) <br /> W = Annual wastewater loading per dwelling unit per acre (inches) = 4.0 inches <br /> (based on 300 gpd/residence) <br /> NW = Nitrate concentration of nitrified leach field effluent (mg/1) = 35 mg/I typical <br /> (Hantzsche and Finnemore (1992)) <br /> D = Percent dentrification of leach field effluent = 0.25 percent (0.1 :o 0.25 <br /> percent typical per Hantzsche and Finnemore (1992). 0.25 selected given <br /> the large depth to groundwater and the presence of irlterbeddsd low <br /> permeable clay layers.) <br /> r = Annual deep percolation of precipitation (inches) = 9.8 inches (representing <br /> 70 percent of the average annual rainfall of 14 inches in project area. <br /> Remaining 30 percent of rainfall is assumed to drain off-site into natural or <br /> manmade drainages) <br /> Nb - Background nitrate concentration of the deep percolating precipitation - mg/I <br /> = 0.5 mg/I (per Technical Memorandum, Hydrologic and Soil Investigation for <br /> the Chico Urban Area, page 6, Dames and Moore, April 1996) <br /> Our calculation is as follows: <br /> Nc = 1.0 (2) (35) (1 -0.25)+ 0.5 (9.8) = 105 +4.9 = 7.96 mg/I as ti <br /> 1.0 (4) + 9.8 4 + 9.8 <br /> we have also used the Hantzsche mass balance equation (source: Predicting <br /> Groundwater Nitrate-Nitrogen Impacts, Hantzsche and Finnemore (1992)), which is <br /> presented below. <br /> NU = I(Nw)(1-D) + R(Nb) <br /> (I+R) <br /> Where: <br /> NC = Average calculated nitrate-nitrogen in groundwater resulting from leach field <br /> source and precipitation - mg/l, as N. <br /> 23187.G02/STOL777 Manu 6.2006 <br /> copyright 2006 Kletnfefder•tnc. Fage 2 of 4 <br />