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Expected On -Site Maximum Septic Tank Usage Maximum expected usage on the Site would be from the current and future residents of the Site. Septic system design should be based on the San Joaquin County On -Site Wastewater Treatment Systems Standards (2017) or other engineering recommendations. Ground Water Information 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 fall of 2017 and spring of 2018 were the most recent available from this source, covering the area of the Site. According to an analysis of these maps (Plates 5 and 6), ground -water elevation is approximately 20 to 23 feet above mean sea level in the area. Ground water appears to flow generally to the north or northwest in the area at a rate of approximately 11 to 16 feet per mile. Given that the ground elevation of the Site is approximately 108 to 110 feet above mean sea level, the depth to water beneath the Site is estimated to be approximately 85 to 90 feet. Potential Ground Water Contamination Issues The Soil Suitability 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, 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. The Site is located approximately one-third of a mile west of the Tracy Defense Depot, a National Priorities List (Superfund) site that has impacted ground water with a variety of chemicals. Detailed discussion of this facility is beyond the scope of this report. 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 7 and 8). According to the maps, eight wells within a one -mile radius of the subject Site have been tested for nitrate; nitrate was detected in three of these wells at concentrations between 5.1 and 10.0 mg/L-N and in five of these wells at concentrations over 10 mg/L-N. According to the DBCP map, four LOGE 2213 Page 3