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Mass Transport Soil Properties <br /> The percolation test has revealed that the surface soils are moderately permeable and <br /> will allow some infiltration of water. The longer the effluent remains near the surface, the <br /> more biologic treatment may occur. If permeable soils exist to the depth of the ground- <br /> water aquifer, it is possible that any remaining surface contaminants may be transported <br /> to the first saturated zone of the aquifer. <br /> Clayey 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 /> 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, only "average recharge rate of rainfall" was considered. <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), preferably from stations located <br /> within San Joaquin County. Recharge is calculated by first determining whether the <br /> average monthly precipitation exceeds average monthly potential evapotranspiration. If <br /> so, then the difference is the percolating recharge water into the aquifer. Runoff and <br /> stream infiltration drainage are not factored into the calculation. This approach likely <br /> under-estimates recharge to the aquifer and, consequently, over-estimates nitrate <br /> loading. <br /> The project Site is located relatively far from any CIMIS stations (10.7 miles to the <br /> closest station) but somewhat closer (8.6 miles) to a station monitored by the Western <br /> Regional Climate Center (WRCC). As a result, two scenarios have been run for the <br /> Site, the first using strictly CIMIS data, and the second using a combination of CIMIS <br /> and WRCC data. <br /> LOGE 20-44 Page 8 <br />