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Soil Suitability /Nitrate Loading Study Irerracon JPM w Lathrop, California May 24, 2022 io Terracon Project No. NA227026 was reported between 12 and 17 feet bgs at two wells located approximately 0.33 miles east of the site. 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 (dibromo chloropropane) 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 the historical information, the past agricultural land use in the area should be considered potential groundwater contamination sources. According to the State Water Resources Control Board website, there were no nitrate impacted wells reported within 2,000 feet of the site. 1.4.3 Water Sample Location A domestic groundwater well is currently located on the eastern portion of the site west of the shop (Exhibit 2). On April 5, 2022 two groundwater samples (GW -1 and GW -2) were collected from the well. Sample GW -1 was collected from a kitchen sink faucet located inside the southern trailer located west of the shop. Sample GW -2 was collected from an exterior faucet located on Responsive ■ Resourceful ■ Reliable 8