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Lee Higgins -3- • 21 September 2011 990 Beechnut Avenue, Tracy • As indicated in the Report of findings, the objective of the remedial activity to remove soil containing elevated PAI-Is and associated nearby crude oil affected soil was completed. • The objective of the remediation was accomplished according to the updated SLRA, and the Site use is suitable for commercial/industrial purposes. According to AMEC's Screening Level Risk Assessment findings: • An area of the Site in the northeast corner at soil boring GMX-13 where ethylbenzene at 0.06 mg/kg was detected at 12 feet bgs, was not addressed by the recent remediation, and presents a potential risk of vapor intrusion. Further assessment or remediation is needed, or engineering controls should be considered if commercial/industrial buildings are built in proximity of GMX-13. • A second area near the northwest corner at boring location GMX-02 was also not addressed by the recent soil removal. TPHc was reported in a soil sample from a depth of 10 feet bgs at a concentration which increased the level of risk for a potential future onsite resident. Further assessment or remediation should be considered if soil at that depth is disturbed during future redevelopment activities. During a recent project meeting, Chevron representatives indicated that a re-evaluation is currently being addressed regarding the two areas discussed, including re-testing and/or subsequent limited soil remediation. Central Valley Water Board staff finds that: • The targeted TPH/PAH affected soil was excavated and properly disposed of offsite. • Once re-evaluation of the two areas discussed above is completed, a workplan is needed describing how the issue of the residual TPHc chemicals, including potential vapor intrusion issues regardless of the likely future Site use, will be resolved to address/update the overall potential risk for the Site. By 1 February 2012, please provide a workplan addressing the residual TPH issues outlined above. If you have any questions or comments, please contact Dean Hubbard at (559) 445- 5179 or by email at dhubbardCa)_waterboards.ca.gov. SHELTON R. GRAY C. DEAN HUBBARD Senior Engineering Geologist Engineering Geologist P.G. No. 6357 C c: Michael Infurna, San Joaquin County EHD, Stockton Gary Foote, AMEC, Oakland