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l n <br /> ✓SOUI'�e3 Of l�litrate <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 /> the also a significant source of nitrate contamination in shallow aquifers in San Joaquin <br /> County. <br /> i <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 a calculation using <br /> average monthly precipitation of rainfall and evapotranspiration rates for Lodi, <br /> California. The calculation first determines whether the average monthly precipitation <br /> exceeds average monthly potential evapotranspiration. If so, then the difference is <br /> potential deep percolation. This method does not consider runoff. Based on the <br /> calculation shown in the following table, the estimated deep percolation of rain <br /> (recharge) for the Lodi, California area is estimated to be 6.57 inches. <br /> Table 4. Estimate of Deep Percolation of Rainfall for Lodi, CA. <br /> Average Rain- Average Potential Potential Deep <br /> Month Fall (inches) Evapotranspiration (inches) Percolation of Rain <br /> (inches) <br /> I January 3.45 0.79 2.66 <br /> February 2.91 1.55 1.36 <br /> March 2.72 3.28 None <br /> April 1-29 5.17 None <br /> May 0.60 6.58 None <br /> June 0.15 7.51 None <br /> July 0.03 7.87 None <br /> August 0.04 6.85 None <br /> September 0.27 5.11 None <br /> October 0.90 3.29 None <br /> November 1.93 1.54 0.39 <br /> December 2.92 0.76 2.16 <br /> Totals 17.20 50.3 6.57 <br /> Notes: CIMiS evapotranspiration information at wwwcimis.water.ca.gov/timid for station 166 Lodi,CA. Rainfall <br /> average from station 045032(Lodi,CA)at www.wrcc.dd.edu. <br /> LOGE0911 Page 9 <br />