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Sources of Nitrate <br /> Septic systems and dairies in the area have been found to be the most significant <br /> s ate in ground water. Orchards that require fertilization in sandy soils are <br /> 2 2) also a significant source of nitrate contamination in shallow or sandy aquifers in San <br /> Joaquin County. <br /> Contribution of Rainfall <br /> An estimate of the quantity and quality of rainfall was required for the nitrate loading <br /> analysis. An estimate of the deep percolation of rain was baseda calculation using <br /> average monthly precipitation of rainfall and evapotranspiration rates for the area. The <br /> calculation first determines whether the average monthly precipitation exceeds average <br /> monthly potential evapotranspiration. If so, then the difference is potential deep <br /> percolation. This method does not consider runoff. Based on the calculation shown in <br /> the following table, the estimated deep percolation of rain (recharge) for the Stockton, <br /> California area is estimated to be 5.98 inches. <br /> Table 3. Estimate of Deep Percolation of Rainfall for North Stockton, CA. <br /> Average Rain- Average Potential Potential Deep <br /> Month Fall (inches) Evapotranspiration (inches) Percolation of Rain <br /> (inches) <br /> January 3.06 0.79 2.27 <br /> February 2.73 1.18 1.55 <br /> March 2.20 3.28 None <br /> April 1.28 5.17 None <br /> May 0.45 6.58 None <br /> June 0.11 7.51 None <br /> July 0.02 7.87 None <br /> August 0.03 6.85 None <br /> September 0.21 5.11 None <br /> October 0.77 3.29 None <br /> November 1.77 1.54 0.23 <br /> December 2.69 0.76 1.93 <br /> Totals 15.33 50.3 5.98 <br /> Notes: CIMIS evapotranspiration information at wwwcimis.water.ca.gov/cimis/for station 166 Lodi. Rainfall average <br /> from station 048560 (Stockton Fire Station#4)at www.wrcc.dri.edu. Closest available stations to Site were selected. <br /> LOGE0914 Page 9 <br />