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Abdelwahed :Facility, Ultramar Site No. 13792 May 9, 2013 Stockton, California _ NFAR Request and Well Destruction Work Plan • soil gas sample SG -3 contained 18% oxygen and 1.7% carbon dioxide; no concentrations of TPHd, TPHg, BTEX, MTBE, DCA or EDB were detected in sample SG -3; • soil gas sample SG -3 DUP collected in the Summa canister and analyzed by ATL contained ._a concentration of 980 µg/m3 TPHg; 34 Pg/m3 toluene; 9.2 pg/m3 ethylbenzene; and 59 µg/m3 xylenes; no concentrations of benzene, MTBE, DCA or EDB were .detected in sample SG -3 (DUP); analytical results of the SG -3 DUP sample confirm the analytical results of sample SG -3 • soil gas sample SG -4 contained 250 gg/m3 toluene, 190 pg/m3 ethylbenzene, 1190 pg/m3 xylenes, 17% oxygen and 1.3% carbon dioxide; no concentrations of TPHd, TPHg, benzene, MTBE, DCA or EDB were detected. in sample SG -4; • no observable loss of vacuum was detected during the 2 -minute shut-in test performed on SG -3 setup; • no leak detection compound concentrations were detected in TEG or ATL soil gas samples; and • quality assurance/quality control data indicate no sampling method or analytical problems. Soil Gas Investigation Conclusions Analytical results of soil gas samples were compared to the shallow soil gas screening levels presented in Table E-2, Shallow Soil Gas Screening Levels for Evaluation of Potential Vapor Intrusion Concerns in Screening For Environmental Concerns At Sites With Contaminated Soil and Groundwater -Interim Final published by the San Francisco Bay RWQCB (revised May 2008) and in Table 2 California Human Health Screening Levels (CHHSLs) for Indoor Air and Soil Gas in Use of California Human Health Screening Levels in Evaluation of Contaminated Properties (January 2005). The soil gas screening levels were developed to screen sites for potential human health concerns and represent concentrations that Cal EPA considers to be below thresholds of concern for risks to human health. The specific environmental protection goal addressed by the environmental screening levels (ESLs) is to protect human health against vapor intrusion into buildings resulting from impacted soil or groundwater. The presence of an analyte in soil gas at concentrations below the corresponding ESLs can be assumed to not pose a significant, long-term (chronic) threat to human health and the environment. Both commercial/industrial (commercial) and residential land -use ESLs and CHHSLs for the analytes are given in the Table 3 for comparison to soil gas analytical results. The screening levels for commercial land use are considered appropriate for this site because the site is not immediately adjacent to residential parcels, the highest soil gas analyte concentrations were detected in the eastern portion of the site away from the residential area west of the site lietween which soil gas analytical results indicate no detectable hydrocarbon concentrations, the land is zoned commercial and is used as an automotive repair shop, and the current zoning is not expected to change in the reasonably foreseeable future. No TPHg, BTEX compounds, MTBE, DCA or EDB were detected above the commercial screening levels. The only analyte detected above any residential screening level was TPHg in 1792 NFAR rpt.doc Project No. 1792.26 6 HORIZON ENVIRONMENTAL INC.