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Mass Transport Soil Properties <br /> The percolation test has revealed that the soils in the test area are moderately <br /> permeable and will allow some infiltration of water. The longer the effluent remains near <br /> the surface, the more biologic treatment may occur. If permeable soils exist to the depth <br /> 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 Manteca station. Data from the Manteca <br /> station were available for 2014 through 2020; based on the calculation shown, the <br /> estimated rate of recharge from percolating waters for the Manteca station is <br /> determined to be 3.23 inches (Plate 12). A statistical error of 58 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 2115 Page 9 <br />