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5 May 30,2018 Page 5 of 7 Reference: Data Gap Assessment Report, Former Chase Chevrolet, 424 North Van Buren Street, Stockton, California approximately five ft bgs to the maximum depth explored (20 ft bgs). Groundwater was encountered within or just above well-graded sand at depths ranging from 13 to 15 ft bgs. Screening Levels for Soil, Groundwater and Soil Vapor - The Work Plan was developed to close data gaps identified from comparison of Site characteristics to the SWRCB LTCP. Therefore, to demonstrate closure of these gaps, results from laboratory analysis of soil, groundwater and soil vapor were compared to media-specific criteria for commercial/industrial sites, as defined in the LTCP. Soil and Groundwater Analytical Results - Soil and groundwater analytical data are summarized in Table 1. GRO, BTEX, MTBE and naphthalene were not detected above laboratory reporting limits (LRLs) in any soil or groundwater sample submitted for analysis. Additionally, LRLs were well below established screening levels for benzene, ethylbenzene, and naphthalene for direct contact and outdoor air exposure, as defined in the LTCP. Screening levels for toluene, xylenes, and MTBE have not been established for soil under the LTCP. Soil Vapor Analytical Results - Soil vapor analytical results are summarized in Table 1. Concentrations of benzene (ranging from 5.4 to 6.5 micrograms per cubic meter [pg/m3]), toluene (ranging from 39 to 50 pg/m3), and xylenes (ranging from 13 to 20 pg/m3 ) were detected in soil vapor samples collected from the three vapor probes (SV-1 through SV-3). Reported concentrations of benzene were well below established screening levels for petroleum vapor intrusion to indoor air, as defined in the LTCP. Additionally, LRLs for ethylbenzene and naphthalene were well below their corresponding established LTCP screening levels. Screening levels for GRO, toluene, xylenes, and MTBE have not been established for soil gas under the LTCP. Atmospheric gases methane (CH4), and helium were not detected above LRLs in any soil vapor sample. Carbon dioxide (CO2) was detected in all three vapor probes in concentrations ranging from 0.21 to 0.27 percent. CONCLUSIONS Site assessment activities described in this report have addressed data gaps previously identified as being impediments to regulatory case closure. Data collected during this assessment confirm that since 2004, concentrations of dissolved-phase petroleum hydrocarbon have decreased to below detectable levels. Concentrations of petroleum hydrocarbons in soil do not represent a potential health threat via direct exposure, and concentrations of aromatic hydrocarbons (benzene, toluene, and xylenes) in soil gas are orders of magnitude below vapor intrusion screening criteria. Because there is no residual plume of dissolved-phase petroleum hydrocarbons associated with the Site, Stantec respectfully requests the Site be granted regulatory case closure without an updated sensitive receptor survey. Soil vapor probes will be abandoned and removed when Site closure is approved. Design with community in mind 4