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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 116 to 146 feet. The <br />vadose zone of the new septic system will be at least 91 feet, and significant <br />nitrate attenuation would be anticipated over the course of this span. <br />• The nitrate level in the on-site well was found to be only 1.4 mg/L-N, despite the <br />existing house and substantial residential development in the area. Based on the <br />map reviewed, nitrate levels in nearby wells do not exceed the MCL. <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 substantially less than predicted. <br />Additionally, Live Oak and Mr. Matthews met with Mr. Shih, Program Coordinator for <br />Land Use at the San Joaquin County Environmental Health Department on April 25, <br />2022. At this time, Mr. Shih indicated that the use of an oversized (2,000 -gallon) septic <br />tank at the second unit dwelling would be sufficient to mitigate nitrate impacts at the Site <br />due to an anticipated 30 percent nitrate reduction in the effluent from the larger tank. <br />LOGE 2226 Page 13 <br />