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Q Limited Phase 11 Subsurface Investigation Report 902-908 East Scotts Avenue Stockton,California a ntea g ro u p Antea Group Project No. UPR82572A grading when the site was developed in the 1800s. PAHs at concentrations indicative of a release were reported at boring B10,coinciding with other contaminants of concern detected in that sampling location. • The testing results reported three metals(arsenic, chromium, and vanadium) at concentrations exceeding EPA's Region 9 RSLs for an industrial setting. The concentrations of both chromium and vanadium are actually less than published background concentrations in California soils. Only one concentration of arsenic (B20 at 1.0-2.5 feet bgs) and barium (also B20 at 2.0-2.5 feet bgs) exceeded the RWQCB direct exposure SSL for trench or construction worker exposure scenario. Antea Group also reviewed the metal data to determine site-specific background trends and determine any anomalously high concentrations relative to the rest of"background" metals concentration in shallow soils at the site. The shallowest samples collected in B16, B17, B20, and B7 all had three or more concentrations of metals that are significantly greater than the sample set and may be indicative of a release. Soil samples in each of those locations also showed PAHs above the laboratory reporting limit, as well as petroleum constituents. • Laboratory results indicate impacts of petroleum hydrocarbons, including exceedances of the ESLs by GRO (in borings B3 and B7), DRO (B2, B7, B10, B16, B17, and B20), and MORO (B7). The MORO concentration of 17,000 mg/kg in B7 exceeds the Direct Exposure SSL for trench worker scenario. Based on the results of this investigation,Antea Group concludes that soils across much of the site are impacted by low levels of contaminants, including metals, polynuclear aromatic compounds (PAHs), and petroleum hydrocarbons (GRO, DRO, MORO). These widespread low levels are may be a background condition of soils due to soils used during initial grading activities during site development in the 1800s, or are widespread minor impacts due to the long-time industrial usage of the property, which has included use or storage of common polluting substances such as coal and oils. Elevated contaminant concentrations indicate several specific areas of environmental concern: • Borings B10 and B7, in the east-central portion of the site. The highest PID readings and concentrations of contaminants of concern, including a trace level of PCBs,were reported in soils collected from these locations. • Borings B3 and B20, beneath the vacant building at 906 E Scotts Avenue (near a floor drain and oil/water separator). Trace levels of VOCs and an elevated concentration of GRO were reported in boring B3. The sample from B20 exhibited elevated DRO, MORO, and metals, including exceedances of trench worker exposure criteria for both arsenic and barium. • Borings B16 and B17, located beneath a building near the southwestern corner of the site, have DRO exceedances,with B17 containing several metal concentrations greater than the site's background levels. • Boring B2 — near the site's pad-mounted electrical transformer, indicates a possible release of oils to the ground surface. PCBs were not detected in B2 soils. 10 www.anteagroup.com