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LOGE 2211 Page 12 within the margin of error of the method, which is highly dependent on off-site rainfall monitoring. Discussion of Nitrate Loading Results Total Nitrate Impact Based on the method and assumptions described, the result of the nitrate loading estimate indicates that the proposed development on the Site has the potential to cause a buildup of nitrates in the aquifer at a level roughly equivalent to the maximum drinking water standard of 10 mg/L-N. There are several mitigating factors that should be considered, however, when evaluating the degree to which the Site is likely to impact ground water with nitrate: • The Hantzsche and Finnemore equation is a conservative method for determining potential impacts, and actual nitrate loading experienced on the Site over time may be less than predicted. The requirement by San Joaquin County Environmental Health Department that the calculation use rainfall and evapotranspiration data to determine ground-water recharge is particularly conservative, as it does not include consideration of recharge from irrigation water or surface water sources. • Depth to ground water beneath the Site is estimated to be 76 to 83 feet. The vadose zone of the new septic system will be at least 51 feet, and significant nitrate attenuation would be anticipated over the course of this span. • Based on the map reviewed, nitrate exceedance in well water does not appear to be a problem in the area. • Based on the clay soil type present on the Site, it is likely that adsorption of nitrate ions to clay will occur as percolating effluent travels downward through the vadose zone. In their original paper, Hantzsche and Finnemore considered developments with relatively shallow groundwater; as a result, the soil factors included in the equation may not reflect the true nitrate reduction experienced as the effluent travels down through a larger vadose zone. Taking these factors into account, the actual nitrate loading experienced on the Site over time will likely less than predicted.