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Live Oak inspected the on-site soil near the proposed new residential area on July 23, 2020. The surface and near-surface soil was found to be sandy clay. Mass Transport Soil Properties The soil type will allow limited infiltration of water through the surface soil. The longer the effluent remains near the surface, the more biologic treatment may occur. In a situation where permeable soils exist to the depth of the aquifer, it is possible that any remaining surface contaminants may be transported to the first saturated zone of the aquifer. First ground water is predicted at 85 to 95 feet below ground surface for this Site; consequently, significant nitrate reduction would be anticipated as the septic effluent percolates downward. Clay soils, like those found on the Site, also tend to inhibit downward movement of nitrate due to adsorption of the nitrate ions to the soil. Groundwater Analysis Depth and Gradient Live Oak reviewed ground-water elevation information available from the San Joaquin County Flood Control and Water Conservation District to estimate the ground-water levels near the Site. Data from the spring and fall of 2016 were the most recent available from this source (Plates 6 and 7). According to an analysis of these maps, the ground-water elevation in the area ranges from 30 to 37 feet below mean sea level, depending on the season; the ground-water flow is to the northeast at a rate of approximately eight feet per mile. Given that the ground elevation of the Site is approximately 55 to 58 feet above sea level, based on the County ground water maps the depth to ground water below the Site is estimated to range from 85 to 95 feet below ground surface. Potential Ground Water Contamination Issues The Nitrate Loading Study is not intended to be an investigation into ground-water contamination sources, and no such investigation was conducted. Many sources can contribute to ground water contamination, including leaking underground storage tanks, agricultural activities, dairies and cattle ranches, septic systems, and storm water infiltration. Agricultural activities and the use of septic systems in the area are known ground-water contamination sources with the potential to impact the Site. Two common ground-water contaminants in San Joaquin County are nitrate and dibromochloropropane (DBCP). Live Oak reviewed the San Joaquin County Environmental Health Department's maps of Nitrate — Land Use Data and DBCP— Land LOGE 20-32 Page 3