SITE INFORMATION AND CORRESPONDENCE

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Michael Oliphant -2 - 11 April 2013 Tracy Byron Road Central Valley Water Board staff notified Chevron in a February 2011 letter that crude oil affected soil and groundwater had been delineated and additional characterization was not needed. The Site was a candidate for closure, and a human health screening evaluation (HHSE) could be prepared. Chevron's consultant submitted the HHSE dated 25 May 2011. According to the 25 May 2011 report, the HHSE was developed in accordance with the Preliminary Endangerment Assessment (PEA) Guidance Manual (California Environmental Protection Agency [Cal EPA] Department of Toxic Substances Control [DTSC], 1999). An incremental lifetime cancer risk of 1 E-06 (i.e., 1 in 1 million), in accordance with the National Contingency Plan, is used as a point of departure for the HHSE. Based on investigative findings, including analytical results, the HHSE estimated that the potential onsite residential land use scenario cancer risk exposure for oral, dermal, and inhalation exposure for Area 1 was 3E-06. This value is slightly above the de minimus level of 1 E-06, but, is within the risk management range of 1 E-06 to 1 E-04. The estimated total potential cancer risk for Area 2 was 9E-07. The non-cancer hazard estimated for the two areas was 0.0004, and 0.005, respectively which are below the hazard index of 1. Area 3 is within a highway/utility corridor easement and is bound to the north and south by sites that were investigated separately and approved for site closure by the San Joaquin County Health Department (1996-1998). Land use in this area will not likely be considered for future residential use and a construction worker scenario was used for the HHSE. The consultant estimated the total potential cancer risk to a hypothetical construction worker from oral, dermal, and inhalation exposure to onsite soils in Area 3 was 4E-07, which is below the de minimus level of 1 E-06. The non-cancer health hazard was 0.04, which is below 1. Thus, the levels of cancer risk for Areas 2 and 3 are below the de minimus level of 1 E-06. These findings indicate an acceptable cancer risk for exposure to onsite soils under those Site condition risk scenarios evaluated. The shallow background water quality at the Site contains naturally occurring high total dissolved solids which exceeds State and Federal standards for some drinking water and agricultural purposes. City of Tracy Municipal code 11.04.160 prohibits use of groundwater within the City sphere for reasons unrelated to the historical crude oil pipelines. SAIC concluded the Site groundwater is not likely to be used as a drinking water source and that alternative municipal water supply sources are available. Therefore, the direct exposure pathway for groundwater was considered incomplete and the HHSE did not quantitatively evaluate that pathway. An ecological screening evaluation indicated that future Site activities are not likely to provide habitat for endangered or threatened species and a threat to sensitive ecological receptors does not appear to exist. SAIC concluded that Site conditions do not pose a health risk to future residents or to sensitive species and therefore no further action is appropriate with respect to onsite soil and groundwater. SAIC's December 2011 Report provided documentation to support Site closure in accordance with Central Valley Water Board'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. Section 6.5 — NFAR for Cases Exceeding Water Quality Objectives should be followed for documenting Site conditions. Previously, SAIC assessed available cleanup technologies and various remedial alternatives for residual crude oil in soil and groundwater at OVP/TAOC projects. The assessment summarized that the residual weathered crude oil is highly viscous, relatively immobile, and primarily occurs within low permeability soil found at the Site. SAIC concluded that affected soil/groundwater has been delineated and in-place management of residual crude oil by natural attenuation is cost effective, feasible, and easily implemented. Concentrations of petroleum hydrocarbons will reduce with time. Based on the alternative cleanup technological assessment and consistent with State Water Resources Control Board Resolution No. 92-049, SAIC concluded there is no known feasible cost effective means, or easily implemented process to effectively remove the petroleum hydrocarbons identified on the Site.