SITE INFORMATION AND CORRESPONDENCE

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No Further Action Required Determi n - 3 - 8 June 2010 Vernalis Offsite Vernalis, San Joaquin and Stanislaus Counties Two groundwater samples were submitted for analysis of TPHd, TPH as gasoline (TPHg), BTEX, and PAH compounds. Concentrations of TPHd were reported at 560 and 660 pg/L, which exceed the taste and odor Water Quality Objective of 100 pg/L for diesel (Marshack, J.B., California Environmental Protection Agency, A Compilation of Water Quality Goals, 2008, July). The remaining petroleum hydrocarbon compounds were ND and/or did not exceed screening levels. The downgradient extent of TPH affected groundwater was not defined and additional delineation was required. • Subsequently, a workplan was approved and in February 2008, additional soil borings were drilled further east, downgradient of the 2005 boring locations to collect samples for analysis. The purpose was to evaluate the downgradient extent of affected groundwater. With the exception of TPHd concentrations of 160 pg/L and 240 pg/L for two of the offset downgradient borings, petroleum hydrocarbon compounds were ND and/or at respective MDLs or less than screening levels. Affected soil was not observed and soil samples submitted for analysis were ND for TPH constituents. Central Valley Water Board staff concurred that additional characterization was not needed. • In November 2008, SAIC submitted a summary report for destruction of the two Site monitoring wells destroyed at the request of the property owner. • SAIC provided a No Further Action Required Request Report (NFAR) for Site closure on 14 August 2009. • On 3 March 2010, Central Valley Water Board staff provided notification to the owner(s) of properties overlying and/or within 200 feet of the approximate boundary of affected soil/groundwater defined at the Site. The notification stated that the Central Valley Water Board was considering a No Further Action determination for the Site and requested comments be submitted within 20 to 30 days. No comments were received. Extent defined: Yes Estimated Residual Petroleum Mass: Unknown. Petroleum occurs in groundwater primarily as degraded crude oil at/near the former Site monitoring wells. Visually affected soil was not observed; analysis of soil samples collected from the maximum depth drilled were ND for TPH compounds. Threat to Groundwater: The OVP pipelines were removed from service more than 35 years ago. The lateral downgradient extent of crude oil affected groundwater has been defined on the Site at approximately 300 feet east of the historical pipelines and former Vernalis pump station facility. Seven water supply wells used for domestic, industrial, irrigation, or public purposes are located within a 2,000-foot radius of the Site; six are located at least 800 feet up/crossgradient of the Site and list minimum sanitary surface seals of at least 50 feet. Surface seal information for the seventh well is unknown. It is unlikely that new groundwater wells will be installed on the Site considering the property is used for agricultural purposes; there are no plans that suggest Site use will change in the future. Threat to Human Health: Chevron's consultant, SAIC considered conservative environmental screening levels based on a residential setting scenario. Based on the applicable environmental screening levels, the Site may be suitable for residential use.