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I Sources of Nitrate <br /> l <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 estimate eR percolation of rain (recharge)-for the Manteca, <br /> California area is estimated to b 3.08 inches per year. <br /> Table 3. Estimate of Deep Percolation of Rainfall for Manteca, CA. <br /> Average Rain- Average Potential Annual Potential Deep <br /> Month Fall (inches) Evapotranspiration (inches) Percolation of Rain <br /> (inches) <br /> January 2.45 0.9 1.55 <br /> February 1.60 1.73 None <br /> March 1.53 3.38 None <br /> April 0.99 5.04 None <br /> May 0.18 6.45 None <br /> June 0.07 7.54 None <br /> July 0.10 8.02 None <br /> August 0.15 7.11 None <br /> September 0.14 5.19 None <br /> October 0.63 3.33 None <br /> November 1.96 1.60 0.36 <br /> December 2.03 0.86 1..1 <br /> Totals 11.83 51.15 3.08 <br /> Notes: CIMIS evapotranspiration information at wwwcimis.water.ca.gov/cimis/for station 70(Manteca, CA). Rainfall <br /> average from station 045303(Manteca,CA)at www..wrcc.dri.edu,Closest available stations to Site were selected. <br /> LOGE101 f Page 9 <br />