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Because ground water is so deep in the area (85 to 95 feet bgs), there is potential for <br /> significant nitrate attenuation before the effluent reaches ground water. Clay-containing <br /> soils, like those observed on the Site, also tend to inhibit downward movement of nitrate <br /> due to adsorption of the nitrate ions to the soil. <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 rate <br /> of recharge from percolating waters, which mix with the downward-percolating effluent <br /> generated by on-site septic systems. In the original Hantzsche and Finnemore paper, <br /> "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 Staten Island station. Data from the Staten Island <br /> station were available for 2016 through 2021 ; based on the calculation shown, the <br /> estimated rate of recharge from percolating waters for the Staten Island station is <br /> determined to be 8.41 inches (Plate 13). A statistical error of 80 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 /> To determine a more accurate local value, Live Oak has collected rainwater during <br /> several recent storm events in Lodi. Each sample was collected in a clean, dry, stainless <br /> steel bowl, then decanted into a plastic container and placed on ice for transport. The <br /> samples were analyzed for nitrate by FGL Environmental of Stockton. The results of the <br /> rainwater sampling are as follows: <br /> LOGE 2245 Page 9 <br />