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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 115 to 145 feet. San <br /> Joaquin County experienced its highest recent ground-water levels in 1983 and <br /> 1999, but no data is available for the Tracy area during these years. Even <br /> assuming a conservative depth to water of 100 feet, the vadose zone of the new <br /> septic system will be relatively deep, extending from the bottom of the system to <br /> 100 feet below ground surface. Significant nitrate attenuation would be <br /> anticipated over the course of this span. To maximize the vadose zone <br /> attenuation, a shallow septic system is recommended. <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 /> For greater protection of the ground water, it is recommended that only a shallow septic <br /> system utilizing leach lines or a filter bed be installed rather than deep seepage pits. It <br /> is the professional opinion of Live Oak that, based on the factors discussed above, <br /> effluent from a shallow septic system on the subject Site is unlikely to contribute <br /> significantly to a build-up of nitrate in the ground water. If seepage pits are desired to <br /> economize on space, the system should be engineered for nitrate mitigation. <br /> LOGE 1914 Page 12 <br />