SITE INFORMATION AND CORRESPONDENCE

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Lee Higgins -2 - 2 December 2010 Former Vernalis Pump Station Vernalis, San Joaquin and Stanislaus Counties agricultural properties. Under regulatory oversight by Central Valley Water Board staff, numerous soil and groundwater investigations were conducted on the Vernalis Offsite (downgradient) properties. The investigations determined that the offsite conditions had been adequately addressed regarding the lateral extent of crude oil affected soil and groundwater. Central Valley Water Board staff notified Chevron in an 8 June 2010 letter that the Vernalis Offsite case could be closed and a No Further Action Required determination was provided. According to SAIC's Screening Evaluation documentation: • Chemicals of potential concern (COPCs) are analytes detected in at least one soil sample between 0 and 10 feet below ground surface (bgs). Low levels of toluene, ethylbenzene, and xylenes, and certain PAHs are considered COPCs and were evaluated quantitatively for the Screening Evaluation. Benzene and the PAHs acenaphthylene and anthracene were not detected in any soil samples and are not considered COPCs. Sixty-seven soil samples from 33 borings were collected and evaluated for the Screening Evaluation. • Site characterization data describes the exposure point concentrations (EPCs) that were used to calculate the upper confidence limit (UCL) for the mean soil concentration of each COPC. If a high number of non-detect (ND) results occur, it may not be possible to calculate a UCL. The United States Environmental Protection Agency (US EPA) recommends that if this condition occurs, to use the sample median as the EPC. • Potential residential exposure to chemicals in onsite soils were estimated for oral, dermal, and inhalation routes following algorithms in the California Department of Toxic Substances Control (DTSC) Preliminary Endangerment Assessment (PEA) Guidance Manual. The algorithms incorporate health protective default exposure parameters promulgated by DTSC and US EPA that represent reasonable maximum exposure for health hazards and health risks. Cancer risks and non-cancer health hazards were estimated using PEA Guidance Manual equations. • 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. A cancer risk equal to or below this threshold is considered to be insignificant. For non-cancer hazard indices, a hazard index of 1 or less is considered an acceptable health hazard level; the non- cancer hazard index was determined to be 3E-03. If regulatory criteria are exceeded based on the findings, the Screening Evaluation identifies the chemical and exposure pathways contributing to the elevated risks or hazards. The risks can be more precisely assessed in a site-specific refined health risk assessment, if warranted. • Since soil and groundwater were delineated, and the characterization dataset adequately describes Site conditions, EPCs were calculated as the UCL of the mean soil concentration for each COPC.