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LOGE 1847: Jhamat SS/NLS Addendum 2 Page 2 <br /> March 18, 2019 <br /> based on the calculation shown, the estimated rate of recharge from percolating waters <br /> for the Staten Island station is determined to be 12.60 inches (Plate 2). A statistical <br /> error of 49% is associated with this value. The two stations are then averaged, for a <br /> regional deep percolation value of 8.16 in. <br /> For this calculation, a denitrification factor of 35 percent was selected for the Site <br /> because of the clayey soils present in the area; you indicated that the Environmental <br /> Health Department has evidence of approximately 30 feet of clay strata within the <br /> vadose zone underlying the Site based on well drilling logs from nearby properties. <br /> The following table presents a summary of the assumptions for, and results of, the <br /> nitrate loading calculation for the Site when recharge is derived by the <br /> evapotranspiration reduction method with CIMIS data. A modified version of this <br /> method is currently being developed by the San Joaquin County Environmental Health <br /> Department for use in future studies. Details of the calculation are presented in Plate 3. <br /> Table 1. Inputs and Results for Nitrate Loading Calculation, <br /> Recharge Derived from Evapotranspiration Reduction Method <br /> Variable Value Units Description <br /> Q 700 gpd Effluent flow rate <br /> Nw 35 mg/L-N Effluent stream concentration <br /> A 1.49 acres Site area <br /> Nb 1.00 mg/L-N Concentration of rain <br /> d 0.35 constant Denitrification factor <br /> R 8.16 inches per year Recharge rate of rainfall <br /> W 6.3 inches per year Uniform waste water loading (calculated) <br /> Nc 10.5 mg1L-N Long-term average concentration of percolating <br /> effluent <br /> For this Site, the long-term average concentration of percolating effluent is found to be <br /> 10.5 mg/L-N when calculated as shown. This value exceeds the US EPA <br /> recommended MCL for nitrate in drinking water of 10 mg/L-N. <br /> There are several mitigating factors that should be considered, however, when <br /> evaluating whether or not this Site is likely to impact ground water with nitrate: <br /> • First, the map of Nitrate — Land Use Data (2019) prepared by San Joaquin <br /> County Environmental Health Department indicates that, within a one-half mile <br />