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--- _- ----- -- a' ;`-- �� KtElNFELnER <br /> File No. 20-2983-03 <br /> October 26, 1990 <br /> f .r <br /> D is the percent denitrification of leach field <br /> effluent - o <br /> r is annual deep percolation of precipitation - inches <br /> Nb is the background nitrate concentration of the deep <br /> percolating precipitation - mg/l <br /> Number of Dwelling Units Per Acre on Septic Tanks <br /> For the purposes of this study we have used a value of A of 1 unit <br /> per acre which is planned for the Mancusco property. We note that <br /> it the housing density within the study area currently varies from <br /> [ approximately 1/2 acre lots to several acres. + <br /> Annual Wastewater Loading Per Dwelling Per Acre <br /> L In the Chico area study, the CRWQCB used a value of 2 inches per <br /> R . year per dwelling for W as the annual wastewater loading. This <br /> figure was based on the assumption that each new home would use an <br /> average of 150 gallons per day. <br /> Nitrate Concentration of Leach Field Effluent <br /> a <br /> This figure was the most difficult to estimate since published <br /> values ranged from approximately 15 to 400 mg/l. The lowest value <br />! San Joaquin County Environmental Health would allow without actual <br /> field measurements was 150 mg/l. Because this value became <br /> critical in determining No, arrangements were made to sample the <br /> i. septic tanks at 5 locations within the study area. These locations <br /> are shown on the Plot Plan, Plate T and were sampled on October 15 <br /> and 16, 1990. The samples were turned over to FGL Analytical <br /> Chemists in Stockton on the same day of sampling and the results <br /> are attached. Surprisingly, the nitrate concentration in the 5 <br /> septic tanks generally proved to be less than 1 mg/l which is less <br /> FA than the nitrate concentration of the water supply. As explained <br /> F - <br /> Copyright 1991 Kleinfelder, Inc. 4 <br />