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September 30,2007 <br /> NOA Project Number: E07146A <br /> /4.0 SOURCES AND IMPACT OF NITRATE TO GROUND WATER <br /> ✓4.1 Current Off-Site Sources of Nitrate <br /> Septic systems, agriculture,and dairies in the area may be the most significant sources of nitrate. <br /> Septic tank use in the vicinity,discussed in Section 3.4 of the SSS,was found to be low. The ground <br /> water sample,discussed in Sections 4.3 through 4.6 of the SSS,was found to have a nitrate <br /> concentration of 7.9 mg/L-NO3. If this sample is typical of groundwater quality,this may indicated <br /> that the ground water aquifer is likely not experiencing nitrate leaching from various sources in the <br /> r� area over the long term. <br /> E ✓4.2 Contribution of Rainfall <br /> An estimate of the quantity and quality of rainfall was required for the nitrate loading analysis. The <br /> estimate of deep percolation of rain is based on the average monthly precipitation of rainfall and <br /> F1evapotranspiration for Lodi,California. An estimate of potential deep percolation of rain water <br /> f recharge into the ground is required for the nitrate loading calculation. <br /> Since the site had rapid percolation rates,we will make the assumption that nearly all rainfall will <br /> infiltrate the ground fairly rapidly. Therefore,we estimate that roughly 80 percent of the rain fall <br /> will enter the ground water as recharge. The 20 percent reduction is to allow for some evaporation <br /> j and transpiration of plants. Runoff is not expected. This method is not appropriate for sites which <br /> do not have relatively high infiltration rates. <br /> F1Based on this method,an estimate for the deep percolation of rain for the site is 14.06 inches. Due <br /> to the soils which allow fairly rapid infiltration, we estimate the deep percolation of rain is based on <br /> 80 percent of the long-term average total rain fall for the Lodi area (http.www.wrcc.dri.edu): <br /> 17.57 inches x 0.8 = 14.06 inches. The nitrate concentration of rainfall was estimated to be 1 <br /> F1mg/L-N (Hantzsche and Finnemore, 1992). <br /> Average potential potrans iration and average rainfall data was obtained from the California <br /> Irrigation Man2#ment Information System (CIMIS).The data from January 1988 to December <br /> 2004 was used fok the <br /> I4.3 Current On-S <br /> F1 .44.3 Current of Nitrate <br /> FI Current on-site sources of nitrate include the current septic system for the residence. <br /> i <br /> Fi. <br /> Fi <br /> 3 <br /> 0 <br /> i �� <br />