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Soil Suitability/ Nitrate Loading Study Irerracon Souza Property Tracy, CA February 28, 2020 Terracon Project No. NA207011 The maximum daily flow rate for the existing residence is 560 gpd and the proposed residence is 420 gpd for a combined total of 980 gpd. 1.4 Groundwater Information 1.4.1 Groundwater Depth and Gradient Groundwater was not encountered within our borings which were drilled between 3 and 10.0 feet below ground surface (bgs). According to the California Department of Water Resources, Groundwater Information Center Interactive Map, in 2018, depth to groundwater was reported between approximately 110 and 120 feet bgs in the Spring and between approximately 120 and 130 feet in the Fall. Based on a review of the San Joaquin County Flood Control and Water Conservation District Groundwater Report, Lines of Equal Depth to Groundwater Spring and Fall 2015 to 2016, depth to groundwater was reported between approximately70 to 80 feet. Based on a review of the sources, depth to groundwater is anticipated to be greater than 80 feet bgs. The groundwater flow direction and the depth to shallow, unconfined groundwater, if present, would likely vary depending upon seasonal variations in rainfall and other hydrogeological features. Without the benefit of on-site groundwater monitoring wells surveyed to a datum, groundwater depth and flow direction beneath the site cannot be directly ascertained. 1.4.2 Potential Groundwater Contamination Issues Potential groundwater contamination can occur from a number of sources including historical petroleum hydrocarbon use, agricultural activities, dairies, septic systems, and storm water infiltration. As per EHD requirements nitrate as N and 1,2-dibromo-3-chloropropane(DBCP) have been included as part of the SSS discussion. Identifying potential groundwater contamination other than nitrates and DBCP is beyond the scope of work for this report. The presence of nitrates is not uncommon in shallow groundwater aquifers in San Joaquin County and other parts of the Central Valley. Nitrate in groundwater occurs as a result of the application of fertilizers, livestock waste, and untreated septic tank waste. Nitrate is mobile and often accumulates in the shallow groundwater zones. In the early 1900s, natural levels of nitrate in groundwater were measured in forty-three (43)wells throughout the Sacramento Valley by Kirk Bryan (1923). It was thought that groundwater at that time was close to "natural" conditions. Based on the work by Bryan, it is estimated that under "natural" conditions, groundwater concentration containing nitrate is no more than about 13.5 milligrams per liter(mg/L) nitrate (NO3) or (3 mg/L-N). Areas having 24.75 mg/L-NO3 (5.5 mg/L- N) or more, are those in which nitrate concentrations may be increasing (Hull, 1984). Responsive ■ Resourceful ■ Reliable 7