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Mass Transport Soil Properties The percolation test has revealed that the surface soils are moderately permeable and will allow some infiltration of water. The longer the effluent remains near the surface, the more biologic treatment may occur. If permeable soils exist to the depth of the ground- water aquifer, it is possible that any remaining surface contaminants may be transported to the first saturated zone of the aquifer. Clayey soils, like those found on the Site, are known to restrict downward movement of water, and may provide nitrogen reduction through adhesion to the soil particles. Sources of Nitrate Dairies, orchards that require fertilization in sandy soils, and septic systems have been found to be the most significant sources of nitrate in ground water. Numerous orchards and septic systems exist in the area surrounding the Site. Percolating Recharge Waters One of the most determinant factors in the Hantzsche and Finnemore equation is the rate of recharge from percolating waters, which mix with the downward-percolating effluent generated by on-site septic systems. In the original Hantzsche and Finnemore paper, only "average recharge rate of rainfall" was considered. Based on San Joaquin County Environmental Health Department policy (personal communication, March 18, 2019), the recharge input for the Hantzsche and Finnemore equation should be derived from average monthly precipitation of rainfall and evapotranspiration rates for the area; the data should be obtained from the California Irrigation Management Information System (CIMIS), preferably from stations located within San Joaquin County. Recharge is calculated by first determining whether the average monthly precipitation exceeds average monthly potential evapotranspiration. If so, then the difference is the percolating recharge water into the aquifer. Runoff and stream infiltration drainage are not factored into the calculation. This approach likely under-estimates recharge to the aquifer and, consequently, over-estimates nitrate loading. For the project Site, the local percolation and evapotranspiration rates are presented in Plate 11. The Site is located closest to the CIMIS Ripon station (249). Data for the Ripon station were available for 2017 through 2019; based on the calculation shown, the estimated rate of recharge from percolating waters for the Ripon station is determined to be 3.00 inches. A statistical error of 34 percent is associated with this value. LOGE 20-19 Page 10