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Expected On-Site Maximum Septic Tank Usage Maximum expected usage on the Site would be from the existing residences and potential new residence. 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 (Plates 5 and 6). No contours are indicated for the Thornton area; the nearest ground-water contours are at ten feet below sea level. The ground-water gradient and flow direction beneath the Site could not be determined. Given that the ground elevation of the Site is approximately 10 feet above mean sea level, extrapolation would suggest a depth to water of 10 to 20 feet below ground surface in the area. San Joaquin County experienced its highest recent ground-water levels in the spring of 1983 and 1999. Review of ground-water maps for these dates (Plates 7 and 8) reveals that depth to water would have been approximately 10 feet in spring of 1999; the Thornton area was not mapped in 1983. 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. 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), only one well within a half-mile radius of the subject Site has been tested for nitrate; no nitrate was detected. According to the DBCP map (Plate 10), one well within a half-mile radius of the Site was tested for DBCP; no DBCP was detected. The Maximum LOGE 1926a Page 3