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LOGE 1907: Bavaro SS/NLS Addendum 3 Page 8 <br /> March 15, 2019 <br /> Results of Nitrate Loading Calculations <br /> For this Site, there is a significant variation between the results of the two methods, 7.4 <br /> mg/L-N by the evapotranspiration reduction method and 3.9 mg/L-N by the reduced <br /> rainfall method. <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 3.9 to 7.4 mg/L-N. The result of the nitrate <br /> loading estimate is well below the maximum drinking water standard. <br /> Uncertainty <br /> For either method of calculating ground-water recharge, and thus nitrate loading, the <br /> calculation should be understood to include a significant amount of uncertainty. For the <br /> evapotranspiration reduction method, the standard deviation of the values for deep <br /> percolation of recharge waters is found to be 1.2 in. The recharge rate can be <br /> expressed as 3.64 in +/- 1.75 in, which results in a recharge rate of 1.89 to 5.39 in. <br /> Uncertainty exists in the other variables as well, including the waste discharge rate, <br /> nitrate concentration of septic effluent, and soil denitrification factor. Nevertheless, <br /> when applied consistently, the Hantzsche and Finnemore equation provides a useful <br /> screening tool to identify situations where mitigation may be advisable to prevent nitrate <br /> impacts. <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 existing development on the Site should not cause a buildup <br /> of nitrates in the aquifer above 10 mg/L-N. Because of the satisfactory result, no nitrate <br /> mitigation measures are recommended. <br />