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as gasoline (TPH-g). Concentrations of lead and arsenic in wells OW-1 through OW-6 were below laboratory reporting limits, with the exception of OW-5 where lead was detected at a concentration of 0.05 milligrams per liter(mg/L) in February 1988 (PG&E, 1989). During the well installation program, it was noted that a layer of black odorous material was encountered near the surface that was suspected to be residue from the former MGP. However, no samples of these materials were submitted to the laboratory for analysis. The locations of these wells along with the historically detected COPCs in groundwater are provided in Figure 8. Analytical results for the soil and groundwater samples collected as part of this investigation are provided in Tables 2 through 5 (soil) and Tables 7 through 10 (groundwater), respectively. It should be noted that the gasoline UST case was closed by the Regional Water Quality Control Board and the San Joaquin County in January 1997. 2.5.4.3 Long Term Groundwater Monitoring for UST Wells Groundwater samples were collected from the OW wells on a quarterly or semi-annual basis between January 1988 and November 1995. Results from the sampling of these wells showed minor detections of the constituents of concern for the gasoline UST (i.e., TPH-g, BTEX and lead) in well OW-2. Well OW-2 was located approximately 10 feet from, and immediately downgradient of, the former gasoline UST. The constituents of concern detected in OW-2 along with the range of results are as follows: • TPH-g—concentrations ranged from 0.009 to 14 mg/L; • Benzene - concentrations ranged from 0.00072 to 1.54 mg/L; • Toluene - concentrations ranged from 0.00084 to 0.64 mg/L; • Ethylbenzene - concentrations ranged from 0.00065 to 0.095 mg/L; • Xylenes - concentrations ranged from 0.00035 to 3.0 mg/L; and • Lead—not detected in any of the samples analyzed. Additionally, sporadic detections of TPH-g, toluene and xylenes were observed in wells OW-3 and OW-6. Results for the COPCs detected in groundwater during previous investigations and this long term groundwater monitoring program are the Site are provided in Figure 8. Based on the results from the groundwater sampling events conducted at the Site and because the impacted soil and product was removed, the case was closed per Regional Water Quality Control Board concurrence letter dated January 2, 1997. In addition, the San Joaquin County Department of Environmental Health (SJCDEH) closed the case in January 1997. In the closure letter, the SJCDEH stated that no additional monitoring was needed and that the wells must be destroyed in order for the Site to be issued a "Remedial Action Completion Certification". As part of the closure, the six wells (OW-1 through OW-6) installed to monitor groundwater impacts associated with the gasoline UST were abandoned. 2.5.4.4 Site Investigation at the Tracy MGP Site Sampling activities were conducted as part of the SI at the Tracy MGP Site in October of 1988. This sampling indicated that potential impacts related to the former MGP operations and releases from the gasoline UST exist at the Site. The predominant contaminants identified at the Site PARSONS 17 FINAL RI REPORT-FORMER TRACY MGP APRIL 2010