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Sources of Nitrate <br /> Septic systems and dairies in the area have been found to be the most significant <br /> sources of nitrate in ground water. Orchards that require fertilization in sandy soils are <br /> 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 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 Escalon, <br /> California area is estimated to be 3.10 inches per year. <br /> Table 3. Estimate of Deep Percolation of Rainfall for Escalon, CA. <br /> Average Rain- Average Potential Annual Potential Deep <br /> Month Fall (inches) Evapotranspiration (inches) Percolation of Rain <br /> (inches) <br /> January 2.46 0.90 1.56 <br /> February 2.08 1.73 0.35 <br /> March 1.93 3.38 None <br /> April 1.02 5.04 None <br /> May 0.46 6.45 None <br /> June 0.13 7.54 None <br /> July 0.02 8.02 None <br /> August 0.04 7.11 None <br /> September 0.17 5.19 None <br /> October 0.63 3.33 None <br /> November 1.24 1.60 None <br /> December 2.05 0.86 1.19 <br /> Totals 12.22 51.15 3.10 <br /> Notes: CIMIS evapotranspiration information at wwwcimis.water.ca.gov/cimis/for station 70 (Manteca, CA). Rainfall <br /> average from station 045738(Modesto,CA)at www.wrec.dri.edu. Closest stations with recent data were selected. <br /> LOGE 1123 Page 8 <br />