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• 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 recharge from irrigation <br />water or surface water sources. <br />• Depth to ground water beneath the Site is estimated to be 88 to 92 feet. The <br />vadose zone of the new septic system will be at least 63 feet (more for a shallow <br />system), and significant nitrate attenuation would be anticipated over the course <br />of this span. <br />• The nitrate level in the on-site well was found to be only 7.5 mg/L-N, despite the <br />existing house and substantial residential development in the area. <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 groundwater; 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 />Taking these factors into account, the actual nitrate loading experienced on the Site <br />over time may be less than predicted. <br />LOGE 2204 Page 14 <br />