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Geosynte& consultants 1. INTRODUCTION Geosyntec Consultants, Inc. (Geosyntec) has prepared this Final Investigation Work Plan— UST 817E (Work Plan) on behalf of the Port of Stockton regarding the former underground storage tank(UST) 817B located at Rough and Ready Island(RRI), Port of Stockton (Figure 1). This Work Plan presents a field investigation to further characterize petroleum constituents in soil, groundwater, and soil vapor within the former UST 817B and surrounding area (the Site). The purpose of this work is to further refine site information to facilitate comparison to general and media-specific criteria in the State Water Resources Control Board's Low-Threat Underground Storage Tank Case Closure Policy(LTCP; State Water Resources Control Board, 2012). This information will be used to evaluate whether the Site poses a low threat to human health and the environment and is suitable for closure under the LTCP or should be assessed under an alternate regulatory framework. This work will be completed under the July 30, 2003, Consent Agreement, which the Port entered into with the State of California, California Department of Toxic Substances Control (DTSC), and the Central Valley Regional Water Quality Control Board(CVRWQCB) for RRI. DTSC is the lead regulatory agency and the CVRWQCB is the supporting agency for environmental work at RRI, except with respect to petroleum USTs and petroleum contaminated sites, for which the CVRWQCB is the lead regulatory agency and DTSC is the supporting agency. UST 817B is a petroleum UST site; therefore, the CVRWQCB is the lead regulatory agency. This Work Plan was originally submitted to DTSC and CVRWQCB on September 27, 2024. The Port of Stockton received comments on the Work Plan from DTSC on November 13, 2024, and a letter from CVRWQCB on November 8, 2024 indicating CVRWQCB's concurrence with the draft Work Plan. This final Work Plan has been revised based on DTSC's comments. A table with responses to comments is included as Appendix A. 1.1 UST 817B Background Building 817B was a former open-air fueling station that housed two fuel dispenser pump islands and a vehicle wash rack. Fuel was stored in four USTs (Figure 2). These USTs reportedly contained gasoline and kerosene. The tanks, pumps, and associated piping were reportedly removed prior to 1997, and Building 817B was demolished in 2007. The UST removals were documented in the Underground Storage Tank UST 817E-2, Tank Removal Summary Report (PRC Environmental Management, Inc. [PRC] 1993) and the UST Closure Report(Smith Technology Corporation 1996)prepared on behalf of the U.S. Department of the Navy (Navy). UST 81713-2 was removed first in 1992 and was noted to have extensive surface corrosion; soil samples collected indicated elevated levels of benzene, toluene, ethylbenzene, and xylenes (collectively referred to as BTEX) and total petroleum hydrocarbons (TPH) as gasoline (TPH-g) were present in soil. Subsequently, the remaining documented tanks, UST 817B-1 and UST 81713-3, were removed in 1996. During this removal, an additional unknown tank("Tank 3") was found and removed(Smith Technology Corporation 1996). Investigation Work Plan—UST 817B 1 December 2024