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of the ground-water aquifer, it is possible that any remaining surface contaminants may <br />be transported to the first saturated zone of the aquifer. <br />Because first ground water is estimated at 85 to 90 feet below ground surface, it is <br />anticipated that significant nitrate reduction will take place as the wastewater percolates <br />through the vadose zone. <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 />The Site is located closest to the CIMIS station at Staten Island (station 242). Data for <br />the Staten Island station were available for the past five years; based on the calculation <br />shown, the estimated rate of recharge from percolating waters for the Staten Island <br />station is determined to be 9.42 inches (Plate 12). A statistical error of 74 percent is <br />associated with this value, largely due to low rainfall in 2020 compared with the other <br />years. <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 20-59 Page 10