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CLEARWATER G R Q U P I N C • Enut—menW Services 4.0 CONCLUSIONS AND RECOMMENDATIONS 4.1 Conclusions Extent of Hydrocarbons in Soil At the request of the San Joaquin County EHD, borings were advanced to evaluate the vertical extent of hydrocarbons in soil below 30 feet bgs Soil samples collected at approximately 30 feet bgs (SB-1, -3, and -4), 35 feet bgs (SB-2 and -5), and 36 feet bgs (SB-6) contained no TPHg, TPHd, or BTEX concentrations above the laboratory reporting limit Analytical results indicate that samples collected in borings to the west (SB-3) and northwest (SB-4) of the UST pit contained no TPHg, TPHd, or BTEX concentrations above the laboratory reporting limit Non-detect to low concentrations of TPHg, TPHd, and BTEX were reported to the southwest (SB-6) of the UST pit Moderate TPH-g and low TPH-d and BTEX concentrations were reported in borings immediately south (SB-1) and southeast (SB- 2) of the UST pit These soil samples were collected below the groundwater table in the saturated zone Extent of Dissolved_H,,Hydrocarbons Analytical results from groundwater samples collected from the three monitoring wells indicate non-detect to very low concentrations of TPHg, TPHd, and BTEX were reported in the assessed upgradient well (MW-2) and the cross-gradient well (MW-3) Elevated concentrations of TPHg and BTEX were reported in the downgradient well (MW-1) No concentrations of TPHo were reported in any of the soil or groundwater samples analyzed Results of analyses from soil and groundwater samples collected during this investigation indicate that a petroleum release has occurred, however, due to the low concentrations detected in the source area, a low hydraulic gradient, and the absence of any identified sensitive receptor in the vicinity, no apparent hazard to human health or the environment is evident and any benefit from active remediation may not be cost effective • 6