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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 /> Clay 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. <br /> A feedlot is adjacent to the north of Site, and 13 other cattle facilities are located within <br /> two miles of the subject 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, "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) stations located within San Joaquin <br /> County. Recharge is calculated by first determining whether the average monthly <br /> precipitation exceeds average monthly potential evapotranspiration. If so, then the <br /> difference is the percolating recharge water into the aquifer. Runoff and stream <br /> infiltration drainage are not factored into the calculation. This approach likely under- <br /> estimates recharge to the aquifer and, consequently, over-estimates nitrate loading. <br /> The closest San Joaquin County CIMIS station to the Site is Manteca (station 70). Data <br /> for the Manteca station were available for the past six years; based on the calculation <br /> shown, the estimated rate of recharge from percolating waters for the Manteca station is <br /> determined to be 3.69 inches (Plate 14). A statistical error of 43 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 20-54 Page 10 <br />