SITE INFORMATION AND CORRESPONDENCE

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Lee Higgins - 2 - 5 August 2010 Chevron Banta Road-UPRR '- The United States Environmental Protection Agency, Suggested No Adverse Response Levels, 1980, describes 100 pg/L as the taste and odor groundwater objective threshold for diesel. (500 mg/L) for drinking water. Additionally, several other constituents exceeded drinking water standards as well as some agricultural beneficial use criteria. Considering the nature of onsite groundwater quality and readily available municipal water supply, shallow groundwater at the Site is unlikely to be used as a drinking water supply. The California Natural Diversity Database (2009) maintained by California Department of Fish and Game, was reviewed by SAIC for threatened, endangered, or sensitive species in the vicinity. None have been observed within one mile of the Site. The environmental screening levels and/or the WQO constituent concentrations are used to assist in defining the extent of affected soil and groundwater, not to assess health, ecological risk, or to establish cleanup levels. The Environmental Risk Evaluation (dated September 2009) findings indicate that exposure to petroleum hydrocarbons chemical of potential concern present do not exceed respective environmental screening levels. The levels do not pose a threat to future commercial/trench maintenance workers or to potential ecological receptors at the Site. In a 10 November 2009 letter to Chevron, Central Valley Regional Water Quality Control Board (Central Valley Water Board) staff concurred that soil and groundwater had been adequately delineated and that a request for an NFAR determination be submitted. SAIC's recent report provided documentation to support an NFAR closure for the Site in accordance with California Regional Water Quality Control Board Central Valley Region's 16 April 2004 update to Appendix A of the Tri-Regional Board Staff Recommendations for Preliminary Investigation and Evaluation of Underground Tank Sites - No Further Action Requests, following Section 6.4 - NFAR Criteria for Cases Above Background Groundwater Conditions. SAIC previously assessed available alternative cleanup technologies and various remedial alternatives for residual crude oil in soil and groundwater at OVP/TAOC projects. The assessment summarized how the residual weathered crude oil is highly viscous and relatively immobile. The crude oil is generally found within low permeability silty clay soil, and Site conditions limit most forms of remediation such as pumping and extraction and/or excavation. SAIC determined that low permeability soil generally limits the migration of the degraded crude oil in the subsurface. SAIC summarized that affected soil/groundwater has been delineated and natural attenuation will reduce the concentrations of petroleum hydrocarbons. Based on the alternative cleanup technological assessment and consistent with State Water Resources Control Board Resolution No. 92-049, SAIC concluded there is no feasible cost effective means, or easily implemented process to effectively remove the petroleum hydrocarbons identified on the Site. Future use of Site groundwater is not anticipated due to low yield, poor quality, and the availability of alternative water supplies.