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Expected On-Site Maximum Septic Tank Usage Maximum expected usage on the Site would be from the existing and proposed residences. 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 spring and fall of 2016 were the most recent available from this source. According to an analysis of these maps (Plates 5 and 6), ground water elevation is approximately 25 to 35 feet below mean sea level; ground water flows down to the east-northeast at a rate of approximately eight to 13 feet per mile. Given that the ground elevation of the Site is approximately 55 feet above mean sea level, the depth to water below the Site is estimated to be approximately 80 to 90 feet. San Joaquin County experienced its highest recent ground-water levels in 1983 and 1999. Review of ground-water maps for spring of these years (Plates 7 and 8) reveals that depth to water would have been approximately 65 to 75 feet. Potential Ground Water Contamination'1 uss es 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. 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. According to the nitrate map (Plate 9), 11 wells within a half-mile radius of the subject Site have been tested for nitrate. Nitrate was detected in seven of these wells at concentrations between 0.1 and 5.0 mg/L-N, and in three at concentrations between 5.1 and 10 mg/L-N. No nitrate was detected in the final well. According to the DBCP map (Plate 10), seven wells within a half-mile radius of the . Site have been tested for DBCP; it was detected in one of the wells at a concentration between 0.01 and 0.2 ag/L; no DBCP was detected in the other six wells. The LOGE 1931 Page 3