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2 polycyclic aromatic hydrocarbons (PAHs); total petroleum hydrocarbons (TPH) as gasoline, diesel and motor oil; volatile organic compounds (VOCs); and Title 22 Metals have been identified in environmental media(soil, soil gas and groundwater) at the Site. Subsequently, the RI was conducted by Parsons, on behalf of PG&E and under the oversight of the DTSC, to further delineate impacts identified during previous investigations. The RI was performed in accordance with the Final Remedial Investigation Workplan (Parsons, 2008), and was conducted in July/August 2008. Based on the preliminary findings, Parsons recommends fiu-ther Site characterization to delineate the lateral extent of potential MGP and gasoline UST related contaminants including: PAHs, TPH, and Title 22 Metals in soil; PAHs, TPH and VOCs in groundwater; and VOCs in soil gas. This Final Technical Memorandum summarizes both the findings of the RI and Parsons' proposal for the Supplemental Site Investigation to fill data gaps for the Site. It should be noted that the gasoline UST case was closed per Regional Water Quality Control Board concurrence letter dated January 2, 1997 and by the San Joaquin County Department of Health Services (DHS) in a letter dated January 15, 1997. The closure determination was based on the results of the long term groundwater monitoring and investigations conducted at the Site for the gasoline UST, and the fact that the impacted soil surrounding the UST was excavated during the removal of the UST. 2.0 SITE DESCRIPTION AND BACKGROUND The Site is located at 502 E. Grant Line Road, in Tracy, California. The Site occupies approximately 5.22 acres of property and is bound to the north by the existing PG&E substation which supplies electricity to a majority of the Tracy area; to the south by Hines Field, a vacant lot; to the east by a recently constructed industrial park; and to the west by railroad tracks owned by Southern Pacific (Figures 1 and 2). There are also residential properties located southwest of the Site just beyond the Southern Pacific Railroad right-of-way. The Site is currently owned by PG&E and is used as a Service Center and electrical substation. A review of historical records indicates that, from 1927 until 1930, an oil gas plant operated at the Site. Based on the description of the Site in the PA (PG&E, 1986), the plant equipment was retired in July 1930 and between 1930 and 1932,the plant was decommissioned. Five investigations have been conducted at the Site since 1986. Results from these investigations showed that elevated levels of PAHs, TPH, and some heavy metals and VOCs were present in soil, soil gas and/or groundwater at the Site. Based on the detections of PAHs, TPH,heavy metals and VOCs,the DTSC requested that an additional investigation be conducted at the Site to determine the lateral and vertical extent of MGP related impacts that remain. In July/August 2008, Parsons conducted an RI at the Site to delineate the extent of MGP related impacts. The following sections summarize the geology and hydrogeology of the Site as well as the data gathered during the RI.