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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 should not cause a buildup of nitrates in the aquifer above 10 mg/L-N. In fact, the actual nitrate loading will most likely be less than calculated. Three mitigating factors should be considered when evaluating nitrate impacts from this Site- • 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 87 to 95 feet. San Joaquin County experienced its highest recent ground-water levels in 1983 and 1999; during spring of those years, depth to water was 65 to 70 feet below ground surface. Even assuming a conservative depth to water of 65 feet, the vadose zone of the new septic system will be relatively deep, and significant nitrate attenuation would be anticipated over the course of this span. • 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. LOGE 1919 Page 12