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BP #172 (Thrifty) - 4 - 9 March 2017 7647 Pacific Avenue Stockton, San Joaquin County A total purgeable petroleum hydrocarbons (TPPH) concentration of 1,000 mg/kg was reported in MW-14 at 30 ft bgs in 2011. Additionally, while soil gas samples collected in 2012 were below the LCTP VI commercial thresholds for Scenario 4 where no bio-attenuation zone exists, three of the five samples were collected from shallower than 5 ft bgs. According to the Department of Toxic Substances Control (DTSC) guidance document Active Soil Gas Investigations --Advisory dated July 2015, "soil gas samples collected at less than 5 ft bgs may be subject to barometric pressure effects and prone to breakthrough of ambient air through the soil column." Samples SV-1 and SV-3 are therefore void as they were collected from a depth of 2 ft bgs. As these sampling locations are closest to the Site building, and therefore data from these samples is most critical to evaluating the VI risk, additional soil gas sampling is needed in order to properly evaluate the VI risk. In order to confirm the VI risk at the Site, an additional round of soil gas sampling should be performed approximately 6 months after remediation has been completed. 5. The Site meets LTCP Direct Contact and Outdoor Air Exposure criteria. Hydrocarbon concentrations in the top 10 feet of soil are below the LTCP criteria, as detailed in Table 3 below. Table 3 — LTCP Direct Contact and Outdoor Air Exposure Criteria and Associated Site Data LTCP Thresholds Residential Commercial/Industrial Utility Site Maximums Chemical Worker Oto5ftbgs 5to10ft Oto5ftbgs 5to10ft OtolOftbgs OtaSft 5to10ft (mg/kg) m 9k (mg/kg) bgs(mg/kg) (mg/kg) bgs bgs Benzene 1.9 2.8 8.2 12 14 <0.02 0.006 Eth (benzene 21 32 89 134 314 0.020 <0.010 Naphthalene 9.7 1 9.7 45 1 45 1 219 1 Unknown Unknown PAH 0.063 NA 0.68 NA 4.5 Unknown Unknown 6. In order to properly assess the nature of the release, waste oil tank samples should be analyzed for total petroleum hydrocarbons as gasoline (TPHg), TPH as diesel (TPHd), total oil and grease (TOG), full-scan volatile organic compounds (VOCs) and semi-VOCs (SVOCs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and Title 22 metals.- According to the November 1995 Tank Removal Report, the sample collected from the former waste oil tank basin was analyzed only for total purgeable petroleum hydrocarbons (TPPH), TPHd, TOG, and benzene, toluene, ethylbenzene, and xylenes (BTEX). In the Work Plan due 19 May 2017, please include a proposal for the collection of shallow soil in the vicinity of the former waste oil tank, with analysis to include: TPHg, VOCs, SVOCs, PAHs, PCBs, and Title 22 Metals. Please also include a proposal for the collection of a shallow soil sample outside of the hydrocarbon impacted area in order to establish naturally occurring background metals concentrations for comparison. 7. Recent Groundwater Monitoring Reports (GMRs) submitted have include figures depicting the distribution of dissolve-phase concentrations in groundwater via chemical