SITE INFORMATION AND CORRESPONDENCE FILE 3

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performed. Active remedial efforts to mitigate the remaining dissolved contaminants would be relatively expensive, and given the relatively low concentrations of petroleum hydrocarbons and fuel oxygenates, the apparent effective attenuation of these contaminants, and the absence of nearby groundwater sensitive receptors, implementation of active groundwater remediation does not appear appropriate. Stratus acknowledges that site specific soil gas data has not been collected. However, it is our opinion that since this property is operated as an active service station (Tesoro), the primary health exposure risks at the site result from active fueling operations, and not from soil gas contaminants that may be present in the shallow subsurface. The site is covered with an asphalt and concrete driving surface, which prevent direct skin contact and exposure to subsurface soils. The asphalt and concrete are not impervious to upward migration of petroleum hydrocarbon laden soil vapors, however these driving surfaces should strongly retard vapor exposure risk from the subsurface. In addition, petroleum hydrocarbon impacted soils were generally detected near the site's USTs and fuel dispensers, which are/were located a significant distance away from the convenience store building, where contaminants could potentially become concentrated in indoor air. Low levels of contaminants may be present in groundwater beneath the site's convenience store building, however these concentrations are expected to be very low given the available data set and, in our opinion, not likely to present a substantial vapor intrusion health risk. In addition, the convenience store has a modern HVAC climate control system, which exerts a positive pressure against inward air migration into the building, and should thus further reduce vapor intrusion risk. Given the reasons cited above,Stratus is recommending against completion of a soil gas survey at the site. It is our opinion that consideration for closure of this site's environmental case may warrant consideration. We acknowledge that concentrations of select petroleum hydrocarbons and fuel oxygenates in groundwater are currently above state-established water quality objectives, however these contaminant levels appear to be attenuating towards water quality objectives without active remedial efforts. Closing the environmental case based on projections of contaminant levels in groundwater towards water quality objectives, given the historical data set, may be justified. Stratus does not recommend that a FS/CAP report be prepared, which would be the first step towards managing the environmental project towards active remediation. The time and expense of implementing a full-scale remedial project does not appear warranted given the contaminant levels beneath the site and current information available regarding exposure risks to potential sensitive receptors. ATTACHMENTS: • Table 1 Groundwater Elevation and Analytical Summary • Table 2 Groundwater Analytical Results for Oxygenates • Table 3 Drilling and Well Construction Summary • Figure 1 Site Location Map • Figure 2 Groundwater Elevation Contour Map, Upper Water Bearing Zone (Second Quarter 2010) • Figure 3 Groundwater Elevation Contour Map, Lower Water Bearing Zone (Second Quarter 2010) • Figure 4 Groundwater Analytical Summary, Upper Water Bearing Zone (Second Quarter 2010) • Figure 5 Groundwater Analytical Summary, Lower Water Bearing Zone (Second Quarter 2010) • Appendix A Field Data Sheets • Appendix B Sampling and Analyses Procedures • Appendix C Laboratory Analytical Reports and Chain-of-Custody Documentation • Appendix D GeoTracker Electronic Submittal Information • Appendix E Dissolved GRO and MTBE Mass Computation Sheets and Associated Figures K UJSA GasolineW835\Quanmiy\2010\USA_835 2Q10.DOC STRATUS L