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water aquifer, it is possible that any remaining surface contaminants may be transported <br /> to the first saturated zone of the aquifer. <br /> Clayey soils, like those found on the Site, are known to restrict downward movement of <br /> water, and may provide nitrogen reduction through adhesion to the soil particles. <br /> Sources of Nitrate <br /> Dairies, orchards that require fertilization in sandy soils, and septic systems have been <br /> found to be the most significant sources of nitrate in ground water. Numerous orchards <br /> exist in the area surrounding the Site. <br /> Percolating Recharge Waters <br /> One of the most determinant factors in the Hantzsche and Finnemore equation is the <br /> rate of recharge from percolating waters, which mix with the downward-percolating <br /> effluent generated by on-site septic systems. In the original Hantzsche and Finnemore <br /> paper, only "average recharge rate of rainfall" was considered. <br /> Based on San Joaquin County Environmental Health Department policy (personal <br /> communication, March 18, 2019), the recharge input for the Hantzsche and Finnemore <br /> equation should be derived from average monthly precipitation of rainfall and <br /> evapotranspiration rates for the area; the data should be obtained from the California <br /> Irrigation Management Information System (CIMIS), preferably from stations located <br /> within San Joaquin County. Recharge is calculated by first determining whether the <br /> average monthly precipitation exceeds average monthly potential evapotranspiration. If <br /> so, then the difference is the percolating recharge water into the aquifer. Runoff and <br /> stream infiltration drainage are not factored into the calculation. This approach likely <br /> under-estimates recharge to the aquifer and, consequently, over-estimates nitrate <br /> loading. <br /> For the project Site, the local percolation and evapotranspiration rates are presented in <br /> Plate 12. The Site is located closest to the CIMIS Ripon station (249). Data for the <br /> Ripon station were available for 2017 through 2020; based on the calculation shown, <br /> the estimated rate of recharge from percolating waters for the Ripon station is <br /> determined to be 2.25 inches. A statistical error of 76 percent is associated with this <br /> value, largely due to the lack of rain in 2020 compared with the other years. <br /> LOGE 2106 Page 9 <br />