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Geosyntec'' consultants Soil sample and chemical test data from a soil boring adjacent to the previous highest area of detections (soil borings 605B02,' which had detections of TPHg, TPHd, and ethylbenzene at concentrations of 250, 83, and 4.2 mg/kg, respectively, from 16 feet bgs [ERS, 2009] and SL60502,2 which had detections of TPHg and TPHd at 100 and 290 mg/kg,respectively, from approximately 16 feet bgs [ERS, 2009]; Figure 3) are required to fill the data gap (RWQCB, 2017 and 2018a). TPHg and TPHd in boring 605B02 were not detected and detected at a concentration of 3.1 mg/kg, respectively, at 7.5 feet bgs (ERS, 2009), but the potential presence of naphthalene in the soil from 0 to 5 feet bgs could not be evaluated because the chemical was not analyzed in previous investigations (RWQCB, 2017). Naphthalene will only be analyzed to fill the data gap. 1.2.3 UST Site 817B Building 817B was an open-air, former base fueling station, housed two fuel dispenser pump islands and a vehicle wash rack, and was supplied by four USTs that reportedly contained gasoline and kerosene,installed adjacent to the building.All tanks,pumps, and associated piping were removed prior to 1997, and the building was demolished in 2007. Since the tank removal,three soil investigations and a groundwater monitoring event have been conducted to characterize the extent of residual contamination in the area (ERS, 2008b). Per the RWQCB's analysis, the site meets general and media-specific criteria for closure under the LTCP program, apart from benzene, which exceeded the LTCP media-specific criteria(RWQCB, 2018a). Samples collected from five soil borings adjacent to the previous highest area of detection (soil borings 817-D2, 817-D3, 817-D4, 817-D5 and 817-D7; Figure 4) are required to fill the data gap (RWQCB, 2017, 2018a, and 2018b). The concentrations of benzene ranged from<0.17 mg/kg (Boring 817-D3) to 22 mg/kg (Boring 817-D5) for samples collected at 4 feet bgs (ERS, 2008b), exceeding the LTCP media-specific criteria. Benzene will be analyzed to confirm if concentration levels are representative of current conditions and to assess if UST 817B meets the criteria for No Further Action(NFA)under LTCP. TPHg and TPHd will also be analyzed to address LTCP media-specific criteria for petroleum vapor intrusion to indoor air(RWQCB, 2018a and 2018b). 'Boring location also referred to as B2 by ERS(2009)and B-2 by RWQCB(2017). 2 Boring location also referred to as 60502 by ERS(2009)and RWQCB(2017). 20190122- FINAL UST Data Gap Work Plan 3 22.01.2019