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The details of the nitrate loading calculation are included on Plate 13. The results of the <br /> calculation are presented in the following table. <br /> Table 4. Result of Nitrate Loading Calculations <br /> Variable Value Units Description <br /> Nc 13.0 mg/L-N Long-term average concentration of percolating effluent <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 13.0 mg/L-N. The result of the nitrate loading <br /> estimate exceeds the maximum drinking water standard. <br /> Discussion of Nitrate Loading Results <br /> Total Nitrate Impact <br /> Based on the method and assumptions described, the result of the nitrate loading <br /> estimate indicates that the proposed development on the Site may cause a buildup of <br /> nitrates in the aquifer above 10 mg/L-N. <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 recharge from irrigation <br /> water or surface water sources. <br /> • Based on the clayey soil type present on the Site, it is likely that adsorption of <br /> nitrate ions to clay will occur as percolating effluent travels downward through the <br /> vadose zone. The soil factors included in the equation may not reflect the full <br /> extent of nitrate reduction experienced. <br /> • According to the San Joaquin County Environmental Health Department's map <br /> reviewed, none of the five wells tested within a half-mile radius of the Site have <br /> exceeded the MCL for nitrate, despite the existing residential development in the <br /> area. <br /> LOGE 20-42 Page 12 <br />