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soils exist to the depth of the ground water aquifer, it is possible that any remaining <br /> surface contaminants may be transported to the first saturated zone of the aquifer. <br /> 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 /> Percolating Recharge Waters <br /> Background <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). Recharge is calculated by first <br /> determining whether the average monthly precipitation exceeds average monthly <br /> potential evapotranspiration. If so, then the difference is the percolating recharge water <br /> into the aquifer. Runoff and stream infiltration drainage are not factored into the <br /> calculation. This approach likely under-estimates recharge to the aquifer and, <br /> consequently, over-estimates nitrate loading. <br /> For the project Site, the local precipitation and evapotranspiration rates are presented in <br /> Plate 14. The closest San Joaquin County CIMIS station to the Site is Ripon (station <br /> 249). Data for the Ripon station were available for the past three years, based on the <br /> calculation shown, the estimated rate of recharge from percolating waters for the Ripon <br /> station is determined to be 3.00 inches. A statistical error of 34 percent is associated <br /> with this value. <br /> Quality of Rainwater <br /> Hantzsche and Finnemore listed 1 mg/L-N as the nitrate concentration of rainwater for <br /> their original calculation; in the past, Live Oak has also utilized this value for the nitrate <br /> loading calculation. <br /> LOGE 1947 Page 10 <br />