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two additional soil gas points (A1-SG2 and Al-SG3) were installed and sampled in an effort to delineate the PCE impacts. Al-SG3 was placed approximately 10 feet upgradient of Al-SGI (relative to groundwater flow direction), and Al-SG2 was placed approximately 10 feet downgradient of Al-SGI. Results from these additional soil gas points showed PCE concentrations of 250 ug/m3 (Al-SG2) and 93.0 ug/m3 (A1-SG3), and that PCE concentrations rapidly decrease in a relatively short distance away from Al-SGI. The source of PCE is not known, but PCE is not associated with MGP residuals or gasoline. Groundwater AOI Groundwater impacts at the Site are limited to AOI 4, located in the northwestern portion of the Site (Grid A3 in Figure 14) where a former gasoline UST was located. This gasoline UST has been removed and residual TPH impacts in groundwater associated with this area were above the Suggested No Adverse Response Level/Taste and Odor Threshold of 100 ug/L during the RI. However, follow-up samples collected during the SSI, showed only two detections (MTBE at 1.1 and 1.2 ug/L) in the samples collected from well TW-5 (TW-5 and Dup-1). Based on these results impacts in groundwater have been delineated. Additionally, based on results of the long term groundwater monitoring conducted at the Site after the gasoline UST was removed, the impacts in groundwater have not migrated off-site. As such, the gasoline UST case was closed per Regional Water Quality Control Board concurrence letter dated January 2, 1997 and by the SJCDEH in a letter dated January 15, 1997. Groundwater in this area has been identified as an AOI but it is anticipated that no remedial efforts will be required to manage impacted groundwater. If future groundwater remedial efforts are required, it is anticipated that they will be limited to monitored natural attenuation. Health Risk Assessment A health risk assessment (HRA) for the Site will be submitted in conjunction with the Removal Action Workplan (RAW). The details of the HRA will be discussed in an HRA scoping meeting between DTSC's Human and Ecological Risk Department (HERD), PG&E, Parsons and Iris Environmental, the health risk assessor for the Site. A technical memorandum that documents the requirements identified for the HRA in the scoping meeting will be submitted to HERD for review and approval. Thereafter, the HRA will be initiated and incorporated into a streamlined HRA/FS/RAW document, to be submitted to DTSC for their review and approval. The results of the HRA will be used to identify those areas of the Site to be targeted for remediation, and to define the ultimate level of remediation that would be required to restore the Site to conditions that would be protective of all potential future land uses to the extent practicable and feasible, given the potential limitations associated with structures and the operating facility. As the overall remedial action objective is to remediate to a point that the Site would have no land-use restrictions and could be used for residential purposes, the focus of this HRA will be to characterize risks to future hypothetical residents and develop appropriate health- based target cleanup goals that would be protective of future on-site residential populations. In the unlikely event that the remediation is not effective in restoring the Site to a condition that is suitable for future on-site activities, a range of commercial cleanup goals can be used to evaluate the types of institutional controls, if any, that may appropriate for the long-term management of the Site. PARSONS 6 FINAL RI REPORT-FORMER TRACY MGP APRIL 2010