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r M. Scott Mansholt Chevron 3 March 2010 Former Tracy Pump Station CURRENT INVESTIGATION The purpose of the current Investigation was to advance one onsite soil boring and collect a water sample to evaluate the vertical extent of crude oil affected groundwater. A sample was collected and submitted for total petroleum hydrocarbon (TPH) analysis. Analytical results were compared to environmental screening levels' (ESLs) and Water Quality Objective (WQO) values for delineation purposes. According to the Report: • Soil boring (SB)-19 was drilled to a depth of 55 feet below ground surface (bgs). A groundwater sample was collected at a depth of 50 feet bgs and submitted for analysis. • Analysis for TPH as diesel (TPHd) was non-detect (ND) and benzene, toluene, ethylbenzene, and xylenes (BTEX) were ND at respective method detection limits (MDLs). Polynuclear aromatic hydrocarbons (PAHs) were ND, and/or detected at low concentrations not exceeding respective WQOs or ESL values with one exception. The detection of benzo(a)pyrene at a concentration of 0.026 micrograms per liter (pg/L) exceeds the WQO of 0.0029 pg/L and the ESL value of 0.014 pg/L. • SAIC contends that with the absence of crude oil related constituents in the groundwater sample, the singular occurrence of the low concentration of benzo(a)pyrene reported is anomalous. • The lateral and vertical extent of affected soil and groundwater have been delineated onsite, upgradient, and crossgradient of the Site. However, the lateral and vertical extent of affected soil and groundwater has not been determined downgradient on the adjacent offsite property. • Since the onsite conditions have been delineated, SAIC is requesting to move forward with Site closure by completing an environmental risk screening evaluation. • Due to frequent delays in obtaining access to the offsite property, SAIC proposes to conduct future investigations separately as the Tracy Pump Station Offsite project. Based on our review, Central Valley Water staff has the following comments: • The lateral and vertical extent of affected soil and groundwater on the Site has been delineated and additional characterization is not needed. 1. San Francisco Bay Regional Water Quality Control Board, 2008, Screening for Environmental Concerns at Sites with Contaminated Soil and Groundwater(Interim Final May 2008). 2. Central Valley Regional Water Quality Control Board, 2007, Water Quality Control Plan (Basin Plan) for the Sacramento River Basin and San Joaquin River Basin, 4'h ed., October.