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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. Clay soils, like those found on the Site, are known to restrict downward movement of water, and may provide nitrogen reduction through adhesion to the soil particles. 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 determine the ground-water levels near the Site. Data from the spring and fall of 2016 were the most recent available from this source (Plates 7 and 8). According to an analysis of these maps, the ground-water elevation is approximately 60 to 63 feet below mean sea level, depending on the season. The ground-water flow is to the east at a rate of approximately six feet per mile for fall 2016; no rate could be calculated for spring 2016. Given that the ground elevation of the Site is approximately 45 feet above sea level, based on the County ground water maps the depth to ground water below the Site is estimated to range from 105 to 108 feet. San Joaquin County experienced its highest recent ground-water levels in 1983 and 1999. Maps of spring ground-water levels were reviewed for this study (San Joaquin County Flood Control and Water Conservation District, 1983 and 1999); the maps show that depth to water beneath the Site was approximately 75 to 77 feet (Plates 9 and 10). 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 Use Data dated February 20, 2019 (Plates 11 and 12). According to the nitrate map, eight wells within a one-mile radius of the subject Site have been tested for nitrate; it was detected in seven wells at concentrations between 0.1 and 5.0 mg/L-N, and was not detected in the last well. Six well within a one-mile radius of the Site were tested for LOGE 1916 Page 3