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2012 TIDEWATER STOCKTON WORK PLAN FOR SEPARATE PHASE HYDROCARBON REMOVAL AT THE WATERFRONT TOWERS PARKING LOT ____________________________________________________________________________ 2 In 1950, the Site and Site Vicinity continued to remain predominantly industrial. Standard Oil ceased operations at the L&M OU by 1950, while Tidewater Associated occupied the entire L&M OU, and Union Oil Company continued to occupy the entire Unocal OU. A lumber storage yard, formerly present on a portion of the Site, was observed as vacant, while Stockton Warehouse Company was the predominant structure remaining. Seaside Oil Company operated a bulk petroleum fuel facility south of the Site from approximately 1947 through 1965. Areas east of the Site were operated by Whol. Liquors & Beer Depot and Star Lumber Yard. Ralston Purina Company, Delta Warehouse Company, California Transportation Company, and Southern Pacific Company were present to the southwest and west (ERI, May 17, 2000). Between 1968 and 1972, expansion of infrastructure occurred in the southern vicinity of the Site. Construction of Highway 4 and Interstate 5 had begun, and the Mormon Channel was redirected through a portion of the former Seaside Oil Company facility. The remaining area formerly occupied by Seaside Oil Company was no longer in existence, and the property became undeveloped. The area continued to remain primarily industrial. Union Oil continued to occupy the Unocal OU and Phillips Petroleum occupied the L&M OU, having purchased it from Texaco in 1966. According to the RDA, the L&M Petroleum site reportedly contained six above- ground storage tanks ranging in capacity from 13,200 gallons to 108,000 gallons, and seven underground storage tanks (USTs) ranging in capacity from 7,500 gallons to 20,000 gallons. Morton Paint Company conducted operations on the southern portion of the Site, which reportedly contained approximately 10 USTs (AGS, October 31, 1989). The San Joaquin Wholesale Grocers and Union Ice & Storage Company were located immediately north of Weber Avenue (ERI, May 17, 2000). In 1977 the principals of L&M Petroleum purchased the bulk storage facility from Tosco, which had purchased the site from Phillips in 1976. In 1980 the RDA took control of the UOU from Unocal. In 1982, the RDA took control of the L&M OU from the principals of L&M Petroleum. At the time, the buildings southwest of the site had been demolished. The western portion of the property was being developed as an apartment complex. The residential area formerly located south of the Site was demolished and left as undeveloped property. The industrial structures on the eastern half of Parcel 2A, and other remaining Site features were removed during 1983, and additional fill materials were reportedly placed in the area by the RDA. The RDA reportedly arranged for the removal of subsurface features including underground storage tanks; however, the RDA has also been unable to provide documentation concerning removal of subsurface features. Buried pipelines and USTs were more recently removed from the L&M OU (on behalf of the L&M Group) in 2004, and the UOU (on behalf of the RDA) in 2008. 1.3 Regional and Local Geology/Hydrogeology Locally, the shallow groundwater bearing zone (A-Zone) primarily extends from the ground surface to depths ranging from approximately 25 feet (ft) below ground surface (bgs) to 40 ft bgs. Subsurface material in the shallow zone predominantly consists of silts, silty sands, and silty gravels from 4 to 10 ft bgs, and then organic clays, clays, high permeability silts, and lenses of silty sands and poorly graded sands to depths ranging from 25 to 40 ft bgs. The shallow zone is generally underlain by low permeability silts and clays (with an occasional, thin, silty sand or poorly graded sand lens) of highly variable thickness. A deeper groundwater bearing zone (B-Zone) is encountered at a depth of approximately 42 ft bgs and extends to approximately