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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 west Tracy, <br /> California area is estimated to be 1.67 inches per year. <br /> Table 3. Estimate of Deep Percolation of Rainfall for West Tracy, CA. <br /> Average Rain- Average Potential Annual Potential Deep <br /> Month Fall (inches) Evapotranspiration (inches) Percolation of Rain <br /> (inches) <br /> • January 2.54 1.33 1.21 <br /> February 2.13 2.19 None <br /> March 1.57 3.91 None <br /> April 0.83 5.53 None <br /> May 0.40 7.79 None <br /> June 0.13 8.89 None <br /> July 0.03 8.98 None <br /> August 0.06 7.96 None <br /> September 0.23 5.97 None <br /> October 0.65 3.96 None <br /> November 1.56 2.05 None <br /> December 1.91 1.45 0.46 <br /> Totals 12.04 60.01 1.67 <br /> Notes: CIMIS evapotranspiration information at wwwcimis.water.ca.gov/cimis/for station 167 Tracy,CA. Rainfall <br /> average from station 049001 (Tracy Pumping Pit.,CA),2/1/1955-6/9/2016, at www.wrec.dri.edu. Closest available <br /> stations to Site were selected. <br /> • LOGE 1623 Page 8 <br />