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lierracon Soil Suitability / Nitrate Loading Study Morada Produce — Ag Processing Building a Stockton, California May 14, 2021 Terracon Project No. NA217014 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 and septic systems 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 Ms. Kristi Friis provided drinking water sampling reports prepared by FGL dated July 8, 2019 and June 26, 2020. Based on a review of the reports, FGL collected a groundwater sample from Well #2 on June 10, 2019 and June 9, 2020. 1.4.4 Groundwater Sample Analysis The 2019 and 2020 FGL groundwater samples were analyzed for nitrate as nitrogen and reported at 5.4 and 5.6 mg/L, below the Maximum Contaminant Level (MCL) of 10 mg/L-N. DBCP was reported below laboratory detection limits of 0.2 micrograms per liter (pg/L) in both samples. The water samples were additionally analyzed for metals. Refer to Appendix G for additional information. 9