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Soil Suitability / Nitrate Loading Study Buddhist Temple Proposed Dormitory • Stockton, California July 11,2019 • Terracon Project No. NA177056 lierracon Refer to Section 2.3.4.1 for further discussion. 1.4 Groundwater Information 1.4.1 Groundwater Depth and Gradient Groundwater was not encountered in our percolation test borings (B1 and B2) excavated to a depth of 3.5 feet below grade surface (bgs). According to the California Department of Water Resources, Groundwater Information Center Interactive Map, depth to groundwater lies between approximately 20 and 40 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. 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). DBCP (dibromochloropropane) is a nematocide and soil fumigant for vegetables and grapes. It is thought to cause health problems consisting of kidney damage, liver damage, and cancer. The use of DBCP was discontinued in 1979. Based on a review of 2006 NOA SSNLS report, the site has a history of elevated nitrate levels in groundwater. Refer to Section 1.1 for further discussion. Responsive • Resourceful • Reliable 9