SITE INFORMATION AND CORRESPONDENCE

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M. Scott Mansholt -2 - 10 November 2009 Chevron Banta Road - UPRR, Tracy Consequently, Central Valley Water Board staff directed Chevron to conduct an additional investigation to determine the extent of crude oil affected soil and/or groundwater. In November 2008, SAIC drilled additional borings to collect soil and groundwater samples for analysis of total petroleum hydrocarbons as crude oil (TPHc), BTEX, and polynuclear aromatic hydrocarbons (PAHs). Visually affected soil was not observed and the results of analyses did not exceed respective environmental screening levels for soil and/or were ND for the petroleum hydrocarbon compounds listed above. Groundwater samples were analyzed for TPH as diesel (TPHd), BTEX, and PAHs. Water samples were also submitted for general minerals analysis for water quality evaluation. The analytical results for TPHd were ND for two samples and 55 micrograms per liter (ug/L) for the third, which is less than the screening level of 100 pg/L considered protective of human health. Additionally, the TPHd concentrations reported are below 100 ug/L, which is the Water Quality Objective (WQO) for the taste and odor threshold for diesel. 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. Based on the investigation findings presented in SAIC's December 2008 report, Central Valley Water Board staff notified Chevron in March 2009 that affected soil and groundwater were delineated, additional characterization was not needed, and an environmental risk evaluation could be submitted. According to SAIC's September 2009 ERE documentation: • Concentrations of the petroleum hydrocarbon compounds considered to be chemicals of potential concern (COPCs) detected did not exceed respective environmental screening levels and thus do not pose a threat to potential future onsite residents, construction/trench maintenance workers, or ecological receptors. • A conservative approach based on a residential scenario was utilized in the ERE, but the most likely future Site use will be for construction/trench maintenance activities within the highway right-of-way and/or the railroad tracks. Residential and/or commercial exposure scenarios are not applicable. • The analytical results for total dissolved solids (TDS) exceeded the California Department of Public Health Recommended Secondary Maximum Contaminant Level value for drinking water. Additionally, several other constituents exceeded drinking water standards as well as some agricultural beneficial use criteria. Considering the undesirable nature of onsite groundwater and readily available municipal water supply, shallow groundwater at the Site is unlikely to be used for drinking water supply. 1 - Marshack, Jon B., 2008, California Environmental Protection Agency, A Compilation of Water Quality Goals, July.