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depth of the ground-water aquifer, it is possible that any remaining surface <br /> contaminants may be transported to the first saturated zone of the aquifer. <br /> First ground water is predicted at 75 to 85 feet below ground surface for this Site; <br /> consequently, significant nitrate reduction would be anticipated as the septic effluent <br /> percolates downward. <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. <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, "average recharge rate of rainfall" was utilized. <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 percolation and evapotranspiration rates are presented in <br /> Plate 15. The closest CIMIS station to the Site is Manteca (station 70). Data for the <br /> Manteca station were available for the past five years; based on the calculation shown, <br /> the estimated rate of recharge from percolating waters for the Manteca station is <br /> determined to be 3.64 inches. A statistical error of 48 percent is associated with this <br /> 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 1945 Page 9 <br />