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• 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 83 to 93 feet. San Joaquin County experienced its highest recent ground-water levels in 1983 and 1999; according to the maps reviewed, depth to water would have been approximately 78 feet in 1983 and 72 feet in 1999. Even assuming a conservative depth to water of 72 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 v 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. • The vicinity of the Site does not appear to be experiencing significant nitrate loading, despite considerable residential development. Nitrate was detected in the water sample collected from the on-site well at a concentration of 6.5 mg/L-N, well below the MCL. According to the San Joaquin County map reviewed, 11 wells within a half-mile radius of the subject Site have been tested for nitrate. Nitrate was detected in eight of these wells at concentrations between 0.1 and 5.0 mg/L-N, in two of the wells at a concentration between 5.1 and 10 mg/L-N, and in only one well at a concentration over 10 mg/L-N. It is the professional opinion of Live Oak that, based on the factors discussed above, effluent from a septic system on the subject Site is unlikely to contribute substantially to a build-up of nitrate in the ground water. LOGE 1920 Page 12