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DRAFT Geosyntec consultants 2. SITE BACKGROUND 2.1 RRI - Historical Use The United States military first established presence on the island after World War L During World War II, the military commissioned RRI as the United States Naval Supply Annex, Stockton. Following the end of the Korean conflict, supply depot activity slowed, and the command changed over time. The Naval Computer and Telecommunications Station San Diego Detachment Stockton managed the depot until July 2002, when Navy operations ceased. Beginning in July 2000, the Navy transferred properties to the Port through the United States Department of Transportation Maritime Administration in three phases. On July 30, 2003 and November 2, 2009, the Port entered into Consent Agreements with the Department of Toxic Substances Control (DTSC) and the CVRWQCB (collectively, the State). The Consent Agreements apply to approximately 560 acres consisting of 37 parcels of land transferred to the Port by the Department of Defense prior to selection of a cleanup remedy. Prior to the transfer of RRI, a Finding of Suitability to Transfer(FOSET) was completed by the Navy(Tetra Tech EM Inc. [Tetra Tech], 2003). According to the FOSET, UST 81713, located in Parcel 182, was transferred with the following closure status: RI report issued in 2001 (TTEI2001a). CVRWQCB concurrence received in letter of March 2002(CVRWQCB 2002b)—no additional RI required; monitored natural attenuation recommended, with more aggressive measures if necessary. No additional information was provided in the FOSET regarding UST 817B. 2.2 UST 817B - Historical Use RRI historically housed USTs that supported various naval activities on the island. The soil and groundwater conditions in the vicinity of the USTs were initially investigated following their removal, and findings were reported to the CVRWQCB in several documents prepared by Tetra Tech on behalf of the Navy, and Environmental Risk Services Corporation(ERS) on behalf of the Port. These documents are referenced in this Report. Building 817B was an open-air, former base fueling station that contained two fuel dispenser pump islands, a vehicle wash rack, and four USTs (USTs 81713-1, 81713-2, 81713-3, and Tank 3) that reportedly contained gasoline and kerosene and were located near the building. The USTs, pumps, and associated piping were removed prior to 1997, and the building was demolished in 2007. Since the UST removal, three soil investigations and multiple groundwater monitoring events have been conducted to characterize the extent of residual contamination in the area. The findings of the previous investigations are summarized in Section 3. 2.2.1 Geology and Hydrogeology RRI is located along the eastern margin of the Sacramento-San Joaquin Delta(Delta) formed by the confluence of several rivers, including the San Joaquin, Sacramento, Mokelumne, Calaveras, and Cosumnes Rivers. RRI consists of 1,459 relatively flat acres that were originally marshy grassland. RRI is located within the legal definition of the Delta, pursuant to California Water Draft Soil and Soil Vapor Investigation 2 August 30,2019