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<br />LOGE 2126 Page 9 <br /> <br />Table 3. Assumptions for Nitrate Loading Calculation <br />Variable Value Units Description <br />Q 400 gpd Effluent flow rate <br />Nw 35 mg/L-N Effluent stream concentration <br />A 1.31 acres Site area <br />Nb 0.17 mg/L-N Concentration of rain <br />d 0.25 constant Denitrification factor <br />R 3.23 inches per year Recharge rate of rainfall <br />W 4.1 inches per year Uniform waste water loading (calculated) <br /> <br />The details of the nitrate loading calculation are included in Plate 11. The result of the <br />calculation is presented in the following table. <br />Table 4. Result of Nitrate Loading Calculation <br />Variable Value Units Description <br />Nc 14.8 mg/L-N Long-term average concentration of percolating effluent <br /> <br />The US EPA recommended MCL for nitrate in drinking water is 10 mg/L-N. In a worst- <br />case situation, the maximum buildup of nitrates in the aquifer from the use of septic <br />systems on the Site is predicted to be 14.8 mg/L-N. The result of the nitrate loading <br />estimate exceeds the maximum drinking water standard. <br />There are three mitigating factors that should be considered, however, when evaluating <br />whether or not this Site is likely to impact ground water with nitrate: <br />• The Hantzsche and Finnemore equation is a conservative method for <br />determining potential impacts, and actual nitrate loading experienced on the Site <br />over time may be less than predicted. The requirement by San Joaquin County <br />Environmental Health Department that the calculation use rainfall and <br />evapotranspiration data to determine ground-water recharge is particularly <br />conservative, as it does not include consideration of regional recharge from <br />irrigation water or surface water sources.