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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 and proposed development on the Site may cause a <br /> buildup of 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 regional recharge from <br /> irrigation water or surface water sources. <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. The soil factors discussed in the Hantzsche and Finnemore paper <br /> may not reflect the true nitrate reduction experienced as the effluent travels down <br /> through the vadose zone. <br /> • According to the San Joaquin County map reviewed, several wells in the area <br /> have been tested for nitrate; none are exhibiting nitrate levels above 10 mg/L-N. <br /> Nitrate was detected in the on-site domestic well at a concentration of 6.2 mg/L- <br /> N. The test results may indicate that residential development in the area has not <br /> adversely impacted water quality. <br /> Based on the factors discussed above, it is likely that the actual nitrate impact to the <br /> ground water will be less than predicted. Nevertheless, it is anticipated that the San <br /> Joaquin County Environmental Health Department may require nitrate mitigation for the <br /> new septic system. <br /> LOGE 1925 Page 12 <br />