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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 nitrate in the aquifer from the use of septic <br /> systems on the Site is predicted to be 12.6 mg/L-N. <br /> Discussion of Nitrate Loading Results <br /> Total Nitrate Impact <br /> Based on the methods and assumptions described, the result of the nitrate loading <br /> estimate indicates that the proposed development on the Site has the potential to cause <br /> a buildup of nitrate in the aquifer over the MCL of 10 mg/L-N. <br /> There are several additional factors that should be considered, however, when <br /> evaluating the degree of nitrate impact to be anticipated as a result of the proposed <br /> construction: <br /> • The Hantzsche and Finnemore equation is a conservative method for <br /> determining potential impacts. 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 /> • Depth to ground water beneath the Site is estimated to be approximately 55 to 60 <br /> feet. Consequently, the vadose zone of the new septic system will be at least 30 <br /> feet, and significant nitrate attenuation may take place over the course of this <br /> span. <br /> • Based on the clay 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. In their original paper, Hantzsche and Finnemore considered <br /> developments with relatively shallow ground water; as a result, the soil factors <br /> included in the equation may not reflect the true nitrate reduction experienced as <br /> the effluent travels down through a larger vadose zone. <br /> • Based on analysis of the water sample collected, nitrate already exceeds the <br /> MCL in the on-site domestic well. The adjacent mobile home park could have <br /> contributed to elevated nitrate levels in the area. <br /> LOGE 2620 Page 13 <br />