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A Aur California Regional Water Quality Control Board 15365 January 30, 2003 Page 3 Concentrations in the 10-foot soil sample collected at location ST/HA-2 were higher than the 4-foot sample, suggesting that a historical release may have occurred in the area. Hart Crowser understands that a Corrective Action Plan is currently being prepared by the STTC to address groundwater impacts in the terminal lease area. AST No. 1503: Four borings consisting of three geoprobe borings to 25 feet(ST/SB-7 through ST/SB-9) and one hand-augered boring to 10 feet below grade (ST/HA-3,) were advanced near AST No. 1503. New fill was observed to depths between 2 and 4 feet, and separate phase product was not encountered. This suggests the excavation conducted near the tank successfully removed diesel from the recent release. Diesel concentrations were low and decreased with depth in the soil samples collected from this area. However, elevated concentrations of diesel were detected in the grab groundwater samples collected from the borings. PROPOSED ASSESSMENT APPROACH Results of the initial assessment of the fuel releases at the site indicate the extent of separate phase product near AST No. 3302 was not defined. Additional assessment will be conducted adjacent to this tank to better define the extent of mobile separate phase product. Groundwater was encountered at approximately 4 feet below grade during the previous investigation. Facility workers at the site report the depth to groundwater is currently about 2 feet below grade. Therefore, we propose to install a series of six lines of shallow(2 to 3 feet deep) test pits moving radially away from the tank to define the lateral extent of the separate phase product in the shallow soil. Figure 2 shows the locations of the proposed test pits relative to the previous boring installations. Separate phase product was not detected near AST Nos. 3301 and 1503, although elevated concentrations of petroleum hydrocarbons were detected in groundwater. Three downgradient monitoring wells (PS/P-10, PS/P-11, and PS/P-12) will be sampled for chemical analysis to assess whether the recent releases have impacted downgradient groundwater. Wells PS/P-10, PS/P-11, and PS/P-12 are not monitored as a part of the terminal lease area sampling program. We understand that PS/P-11 and PS/P-12 have historically contained separate phase gasoline product, and these wells will be gauged for the presence of product prior to sample collection. Results from the groundwater monitoring activities will be compared to historical results obtained from these wells to evaluate whether significant changes in water quality or product thickness has occurred. In addition, a regional remedial action plan is currently being developed by the STTC to address groundwater impacts from past operations at the terminal lease area, including the ST Services facility.