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Soil Suitability/ Nitrate Loading Study Irerracon Manteca Farm Improvement Manteca, California October 29, 2019 Terracon Project No. NA197073 1.4 Groundwater Information 1.4.1 Groundwater Depth and Gradient Groundwater was not encountered within our borings which were advanced between 3.5 and 10.0 feet below grade surface (bgs). Based on a review of a Geotechnical Engineering Investigation Proposed Delta Farm Improvements dated April 26, 2019 prepared by Krazan &Associates Inc. (Krazan) Project No. 072-19013, groundwater was encountered at approximately 34.5 feet bgs. According to the California Department of Water Resources, Groundwater Information Center Interactive Map Spring and Fall 2018 depth to groundwater was reported between approximately 30 and 40 feet bgs. Groundwater appeared to flow in a northeasterly direction. 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). 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 the State Water Resources Control Board online map, there were no nitrate impacted wells identified within 2,000 feet of the site. Based on the historical information, the Responsive■ Resourceful ■ Reliable 8