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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 />Clay soils, like those found on this Site, 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 <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 Staten Island station. Data from the Staten <br />Island station were available for 2016 through 2020; based on the calculation shown, <br />the estimated rate of recharge from percolating waters for the Staten Island station is <br />determined to be 9.42 inches (Plate 16). A statistical error of 74 percent is associated <br />with this value. <br />Qualitv 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, <br />stainless steel bowl, then decanted into a plastic container and placed on ice for <br />LOGE 2153 Page 10 <br />