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6.0 CONCLUSIONS AND RECOMMENDATIONS Based on the data from the visual survey and the limited GPR and EM geophysical surveys, no former UST excavations and/or in-place USTs were identified in the survey areas. However, the results of the GPR and EM surveys cannot definitively confirm or rule out the presence of USTs in the project area. Unidentified magnetic anomalies were observed to the east of the service station building consistent with possible underground utility lines. The concrete pad surrounding the pump island contained rebar, which interfered with GPR and electromagnetic readings in that area. TPHd was detected in soil samples from the hand-auger boring and seven of the eight direct-push borings, at concentrations ranging from 17 mg/kg to 8,600 mg/kg. TPHd was not reported in boring DP8, west of the station, but the overall vertical and lateral extent of contamination has not been defined. When drilling Boring DP2, the boring nearest the fuel pump, strong hydrocarbon odors were noted in the samples. Based on the sample results and field observations, TPHd contamination is greatest in the vicinity of the fuel dispenser. The 0.3 in sample from boring DP2 was reported to contain 3,600 mg/kg TPHd, as well as 3,800 mg/kg at 2 in. In the other four borings drilled around the fuel island (DPI, DP3, DP4 and DP7) TPHd concentrations in excess of 1,000 mg/kg were only reported from the samples collected at or below 2.0 in. This is interpreted to be due to lateral migration along preferential pathways stemming from a source in the area of the fuel dispenser. The highest concentration of TPHd was reported in sample DP3-2 from north of the fuel pump, indicating a possible preferential migration pathway in that direction. TPHd was also reported in boring HA1 at the intake for the AST fill pipe and in boring DPS, which was advanced where the AST fill pipe enters the fuel AST. The highest concentration of TPHmo was reported in sample DP2-2 from boring DP2, the boring nearest the fuel pump. The soil samples did not contain metals in excess of their respective TTLC or STLC values. Based on a comparison with levels reported in Background Concentrations of Trace and Major Elements in California (1996) by G. R. Bradford, A. C. Chang, A. L. Page, D. Bakhtar, J. A. Frampton, and H. Wright, the metals concentrations reported are consistent with naturally occurring background concentrations for San Joaquin County soils. Based on the soil impacts discovered in the areas of the fuel dispenser, fill pipe, and AST, further environmental investigation at the Site is warranted. Additional investigation should be performed to delineate the horizontal and vertical extent of the TPHd soil contamination. The installation of three groundwater monitoring wells is recommended to determine if groundwater under the Site has been impacted and to determine the direction of groundwater flow. USTs, septic systems and/or water wells encountered at the Site during subsequent site demolition and/or grading operations should be removed in accordance with SJCDEH requirements. Project No S8475-06-70 -10- July 9,2003