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Soil Suitability / Nitrate Loading Study 11065 North Alpine Road I Stockton, California r rerracon June 30, 2026 1 Terracon Project No. NA267068 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, and in good working condition, 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 nitrogen-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 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 is a nematicide 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 historical information, the past agricultural land use in the area should be considered a potential groundwater contamination source. 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 One groundwater well was identified onsite and associated with the current residential property located on the southern side of the property. A detailed site diagram map showing the approximate location of the well is included in Appendix A (Exhibit 2). A groundwater sample was collected from a hose bib attached to the well head. Facilities I Environmental I Geotechnical I Materials 8