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ASSOCI ATE S I N C . ' 3. Petroleum hydrocarbon-affected soils are present primarily the vadose zone at approximately 10 to 15 feet bgs. The highest concentrations of TPHg and benzene are present in soil under the fill end of the gasoline UST. The petroleum hydrocarbons appear to attenuate rapidly with depth as indicated greatest by soil sample ET-SB4-20, ' collected from S134 at 20 feet bgs, which contained only trace levels of toluene (0.0071 mg/kg), xylenes (0.021 mg/kg), and TPHg (0.13mglkg). Rapid vertical attenuation of hydrocarbons is also evidenced by soil sample ET-SB1-30.0, collected at 30 feet bgs, ' which contained only trace levels of toluene (0.064 mg/kg), and xylenes (0.012 mg/kg). 4. Of the ten soil samples analyzed to date, only one sample (ET-SB 1-15.0) was reported to contain benzene above the laboratory method detection limit (MDL). The reported benzene concentration of in sample ET-SB 1-15.0 is 0.90 mg/kg. 1 5. Soil samples collected in July 1997 were analyzed for MTBE by EPA Method 8020. MTBE was not detected in the soil samples above the laboratory MDLs. 6. In April 1999, at the request of PHS/EHD, ATC completed a receptor survey for the subject property. ATC reviewed PHS/EHD groundwater well construction logs, Department of Water Resources (DWR) groundwater well construction logs, and conducted a site walk in the vicinity of the site to identify any groundwater wells located within a 2,000-foot radius of the site. This survey revealed fourteen wells located within approximately 2,000 feet of the site. The closest of these wells is located approximately 800 feet upgradient of the project site. 6.0 EVALUATION OF LOW RISK CRITERIA 6.1 Low Risk Soils-Only Case Evaluation Using the criteria listed in CRWQCB's No Further Action (NFA) requirements, as outlined by ' CRWQCB (Appendix B of the Tri-Regional Recommendations), conditions at the subject site were evaluated to determine if NFA as a "low risk, soils only site" is appropriate for this site. ' Criterion 1: The leak has been stopped and the sources, including free product have been removed or remedied. In April 1997, two 1,000-gallon regular gasoline USTs and associated piping, and fuel dispenser were removed by SEMCO. ' w:1943041reponslc1osure.doe 5