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Sources of Nitrate <br /> Septic systems and dairies have been found to be the most significant sources of nitrate <br /> in ground water. Orchards that require fertilization in sandy soils are also a significant <br /> source of nitrate contamination in shallow or sandy aquifers in San 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 based on a 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 5.62 inches per year. <br /> Table 3. Estimate of Deep Percolation of Rainfall for Stockton, CA. <br /> Average Rain- Average Potential Annual 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 1.55 1.18 <br /> March 2.19 3.28 None <br /> April 1.30 5.17 None <br /> May 0.46 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 0.22 5.11 None <br /> October 0.79 3.29 None <br /> November 1.76 1.54 0.22 <br /> December 2.71 0.76 195 <br /> Totals 15.37 50.3 5.62 <br /> 7 <br /> Notes: CIMIS evapotranspiration information at wwwcimis.water.ca.gov/cimis/for station 166 Loch, C-A-,Rainfall C3 2\ <br /> average from station 048560 (Stockton Fire Station 4, CA) at www.wrce.dri.edu. Closest available stations to Site <br /> were selected. <br /> LOGE 1515 Page 9 <br />