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Soil impacts identified in AOI 4 showed elevated B(a)P equivalent concentrations in RI Boring A3-2 to a depth of 1 foot bgs. Thereafter, all samples were below 0.9 mg/kg for B(a)P equivalents. Borings TB-1, TB-8 and TB-32 showed no detectable concentrations of PAHs. TPH concentrations in this AOI varied. The highest TPH-g concentration in the RI/SSI samples was observed in Boring A3-2 at 10 feet bgs was 200 mg/kg. However, a TPH-g concentration of 840 mg/kg was observed in the soil boring for well OW-2 at a depth of 8-8.5 feet bgs. The highest concentrations of TPH-d and TPH-mo in this AOI were observed in Boring A3-2 at a depth of 1 foot bgs at concentrations of 130 and 1,000 mg/kg, respectively. The only detection of TPH observed in the borings used for lateral delineation (i.e. TB-1, TB-8 and TB-32) was a detection of TPH-g (20.0 mg/kg) at 7.5-8 feet bgs in Boring TB-32. Based on this information, soil impacts in this AOI have been delineated. Soil gas samples collected from A3-SG1 showed elevated VOC concentrations for chemical typically encountered with leaking USTs (i.e., BTEX, trimethylbenzenes, etc.). Based on the RI data for soil gas samples, an additional 5 soil gas points (A3-SG2 through A3-SG6) were installed to laterally delineate impacts identified in A3-SGI. Results from the additional soil gas points showed concentrations several orders of magnitude below those observed in A3-SG1 and below residential CHHSLs in shallow soil gas. Additionally, these concentrations are not elevated relative to the other soil gas points at the Site. Based on these results, soil gas impacts in this AOI have been delineated. As previously stated, RI Boring A3-2 was converted into groundwater monitoring well TW-5. Results from the groundwater samples collected from TW-5 during the RI showed concentrations of TPH greater than the Suggested No Adverse Response Level/Taste and Odor Threshold of 100 ug/L for TPH as diesel. In addition, low levels of VOCs were detected in groundwater samples collected from TW-5. Based on these results, the DTSC requested that additional samples be collected from this well during the SSI to determine if the results are reproducible. Results from the SSI sampling showed no detections of PAHs and/or TPH in groundwater. Additionally, only one VOC (MTBE) was detected in groundwater during the SSI, relative to the five VOCs (1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, n-butylbenzene, m,p- xylenes and o-xylenes) detected during the RI. Based on these data points, impacts in groundwater have been delineated. 4.4.5 AOI 5 The fifth AOI at the Site is associated with soil gas at the Al-SG1 location. The soil gas sample collected from this location during the RI had an elevated detection of PCE. The detected concentration (1,500 ug/m3) was above the commercial CHHSL for PCE in shallow soil gas of 603 ug/m3. Based on this detection, additional soil gas points (Al-SG2 and Al-SG3) were installed at the Site. Soil Gas Boring Al-SG2 was installed approximately 10 feet downgradient (relative to groundwater flow direction) and A 1-SG3 was installed approximately 10 feet upgradient of the Al-SG1 location. Results from these samples showed concentrations of PCE at 250 and 93.0 ug/m3, respectively, and that PCE concentrations rapidly decrease in a relatively short distance away from Al-SG1. As such, Al-SG2 and Al-SG3 delineate soil gas impacts identified in Al-SGI. The PCE source is not known. PARSONS 40 FINAL RI REPORT-FORMER TRACY MGP APRIL 2010