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. i h� KLEINFELDER <br /> File No. 20-2921-0 i <br /> March 25, 1992 <br /> Nc = AW x Nw (1-D) + (Nb) <br /> AW + r <br /> Where: NC is the nitrate concentration in <br /> groundwater resulting from domestic <br /> sources and precipitation - mg/1 <br /> A is the number of dwelling units per acre <br /> on septic tanks - unit/acre <br /> W is the annual wastewater loading per <br /> dwelling per acre - inches <br /> ' on of nitrified <br /> Nw 1.s the nitrate concentrate <br /> leach field effluent - mg/l <br /> D is the percent denitrification of leach <br /> field effluent - % <br /> r is annual deep percolation of <br /> precipitation -- inches <br /> Nb is the background nitrate concentration of <br /> the deep percolating precipitation - mg/l <br /> Number of Dwelling Units Per Acre on Septic Tanks <br /> For the purpose of this study we have used a value of A of 1 <br /> unit per acre which is planned for the Morada Meadows <br /> subdivision. We note that the housing density within the <br /> I' study area currently consists of only a few residences <br /> k throughout the area. <br /> i <br /> Annual Wastewater Loading Per Dwelling Per Acre <br /> In the Chico area study, the CRWQCB used a value of 2 inches <br /> per year per dwelling for W as the annual wastewater loading. <br /> This figure was based on the assumption that each new home <br /> wo ld u _ <br /> se an average' of 150 galll s per day. <br /> Nitrate Concentration of Leach Field Effluent <br /> This figure has been the most difficult to estimate since <br /> published values range from approximately 15 to 400 mg/1. <br /> Because this value is critical in determining Nc, for <br /> previous nitrate loading studies performed by our firm we <br /> sampled numerous septic tanks. Without exception, the <br /> samples produced test results indicating nitrate <br /> concentrations of less than 1 mg/l. As explained in a letter <br /> dated October 24, 1990, prepared by John Quinn, laboratory <br /> director for FGL Environmental, nitrate is being destroyed <br /> Copyright 1992 KLeinfelder, Inc. Page 5 of 9 <br />