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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 73 to 78 feet. The <br /> vadose zone of the new septic system will be at least 48 feet, and significant <br /> nitrate attenuation would be anticipated over the course of this span. <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 /> • Based on testing data from nearby wells, it appears that nitrate levels in the <br /> vicinity of the Site do not exceed 10 mg/L. Nitrate contamination does not <br /> appear to be a problem in the area despite substantial residential development. <br /> Based on the factors above, the actual nitrate impact to ground water beneath the Site <br /> may be considerably less than predicted, and it is the opinion of Live Oak that an <br /> engineered nitrate-mitigating septic system is not warranted in this location. <br /> LOGE 2118 Page 13 <br />