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6.1.2 Analytical Results—Soil A total of 83 on-site soil samples and five off-site background soil samples were collected during the RI/SSI. A summary of the analytical results is provided below: • The highest concentration of CPAHs in on-site soil were observed at the B1-1 location, at a depth of 1-foot bgs, where chrysene was detected at a concentration of 15,000 ug/kg. This sample also had the highest B(a)P equivalent concentration (18.746 mg/kg). An additional six samples had elevated B(a)P equivalent concentrations (i.e. >0.9 mg/kg) at concentrations ranging from 0.9059 to 10.414 mg/kg; • The highest concentrations of TPH in on-site soil were observed in Boring E3-1, at a depth of 10-feet bgs, where TPH-mo was detected at 13,000 mg/kg; • Metals concentrations observed on-site were similar to those identified in the background samples collected from the industrial areas surrounding the former Tracy MGP Site. The highest metal concentration in soil was observed in Boring B1-1, at 5- feet bgs, where barium was detected at 1,160 mg/kg. • The highest VOC concentration in soil was observed in the samples collected adjacent to the former gasoline UST. These on-site samples identified naphthalene as the highest VOC detected, with a reported concentration of 8,800 ug/kg. However, soil gas results from this same location showed no detectable concentrations of naphthalene. • Background samples collected as part of the RI/SSI had relatively low concentrations of PAHs and TPH. With the exception of background sample BK-TR-4, metals concentrations were relatively similar in the number of constituents identified and their concentrations. Background sample BK-TR-4 was collected in a non-industrial area (i.e., residential) and results for this sample are slightly lower than the other background sample results. 6.1.3 Analytical Results—Soil Gas Soil gas results for the RI/SSI were elevated at two locations, Al-SG1 and A3-SG1, where additional sampling was conducted for delineation of impacts. At Al-SG1, PCE was detected at elevated concentrations; however, results from delineation borings Al-SG2 and Al-SG3 (installed within 10 feet of Al-SG1) showed that concentrations decrease rapidly in a relatively short distance away from Al-SG1. The second location with elevated soil gas results (A3-SG1) was identified in the area immediately adjacent to the former gasoline UST. Results showed elevated concentrations of gasoline related constituents including the following: BTEX, trimethylbenzenes, and propylbenzenes. The highest detected soil gas VOC concentration observed was 230,000 ug/m3 of 1,2,4-trimethylbenzene. Based on these results, an additional five soil gas points (A3-SG2 through A3-SG6) were installed and results were several orders of magnitude below those detected in A3-SG1, and below residential California Human Health Screening Levels (CHHSLs) in shallow soil gas. PARSONS 46 FINAL RI REPORT-FORMER TRACY MGP APRIL 2010