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"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. In 1989, PG&E prepared a report for the Site Investigation (SI) for the Tracy MGP Site (PG&E, 1989) documenting results of a sampling effort conducted at the Site in October 1988. The SI was conducted in a manner similar to a Preliminary Endangerment Assessment. The SI consisted of the drilling and sampling of 33 soil borings, the installation of five new monitoring wells (TW-1 through TW-4, and TP-1), and the sampling of 10 of the 11 monitoring wells at the Site (six of which were installed to monitor releases from the former gasoline UST). Monitoring well TP-1 was installed for the purposes of measuring the potential vertical groundwater gradient and no environmental samples were collected from this well. Analytical results from the soil sampling during the SI showed detectable levels of PAHs, total petroleum hydrocarbons (TPH) and BTEX in soil. Title 22 Metals were detected throughout the Site; however, a large majority of the sample results appear to be indicative of background conditions. The results from the soil samples showed that MGP related impacts appeared at a maximum depth of approximately four feet below ground surface (bgs). In the northwest corner of the Site in the vicinity of the former gasoline UST, other compounds (BTEX and TPH-g) not necessarily related to MGP operations were encountered. The BTEX impacts in the area near the former gasoline UST were below 1 mg/kg with the exception of one boring (TB-32). Groundwater samples collected during the SI showed limited impacts related to MGP operations. However, groundwater samples collected from well OW-2, in the vicinity of the former gasoline UST, showed impacts from the gasoline UST (i.e., TPH and BTEX). The SI soil sampling locations and corresponding analytical results are presented in Figure 6 and the soil gas sampling results from previous investigations are presented in Figure 7. In addition, the reported groundwater data from the SI and supplemental groundwater sampling events conducted at the Site are provided in Figure 8. Remedial Investigation/Supplemental Site Investigation In 2008, Parsons was retained by PG&E to delineate the lateral and vertical extent of impacted soil, soil gas, and groundwater resulting from historical gas manufacturing operations as well as subsequent operations that may have impacted environmental media at the Site. The range of chemical analyses and the placement of the soil/soil gas/groundwater sampling locations were determined based on findings of previous Site investigations (PG&E, 1986 and 1989). The United States Environmental Protection Agency (USEPA) Data Quality Objectives process was utilized to facilitate the design of the sampling approach (USEPA, 2000). Site Remedial Investigation activities were conducted in two separate phases: Phase 1 was implemented in July/August 2008 as outlined in the Remedial Investigation Workplan (Parsons, 2008); and Phase 2 was conducted in April 2009 to fill data gaps identified during the Phase 1 investigation activities as documented in the Final Technical Memorandum - Supplemental Site Investigation for the Delineation of Data Gaps Identified During the Remedial Investigation (Parsons, 2009). The sampling associated with the Phase 1 and 2 investigations included the advancement and sampling of the following: 15 soil borings; 22 soil-gas probes; the installation of one new monitoring well (TW-5); the collection of grab groundwater sample (E3-2GW); and the development and sampling of five groundwater monitoring wells (TW-1 through TW-5) at PARSONS 3 FINAL RI REPORT-FORMER TRACY MGP APRIL 2010