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of the ground-water aquifer, it is possible that any remaining surface contaminants may be transported to the first saturated zone of the aquifer. Clay soils, like those found on this Site, tend to inhibit downward movement of nitrate due to adsorption of the nitrate ions to the soil. 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. A mobile home park is located adjacent to the south of the Site. This land use is typically associated with substantial wastewater discharge. 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, "average recharge rate of rainfall" was utilized. 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. The closest CIMIS stations to the Site are Holt (station 248) and Linden (station 262). Data for the Holt station were available for the past nine years; based on the calculation shown, the estimated rate of recharge from percolating waters for the Holt station is determined to be 3.99 inches (Plate 15). A statistical error of 54 percent is associated with this value. Data for the Linden station were available for the past five years; based on the calculation shown, the estimated rate of recharge from percolating waters for the Linden station is determined to be 8.75 inches (Plate 16). A statistical error of 23 percent is associated with this value. The estimated rates of recharge from the two stations were then averaged, for an estimated rate for the Site of 6.37 inches. LOGE 2620 Page 9