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BUILDING 16 FORMER USTS GROUND WATER INVESTIGATION WORK PLAN PORT WEST COMPLEX, ROUGH AND READY ISLAND,PORT OF STOCKTON 2.2 DESCRIPTION OF BUILDING 16 SITE The Building 16 Site consists of approximately 0.5 acres covered with asphalt, an empty building, and grass landscaped areas. The topography of the Site is flat, averaging approximately 3 feet above mean sea level. The San Joaquin River is approximately 1,000 feet south of the Site. The Site was originally developed as a gasoline service station in 1963 and operated until 1997. Based on the dates of operation, the gasoline stored and dispensed at the Site likely included the additives lead and MTBE. Three USTS were present at the Site in the locations shown on Figure 4. The following summarizes the three former USTS: UST ID Contents Capacity Material Installed Removed 16-1 gasoline 5,000 gal single wall steel 1963 1997 16-2 gasoline 5,000 gal single wall steel 1963 1997 16-3 gasoline 10,000 gal single wall fiberglass 1975 1997 Building 16 has not been used since 1997 and is abandoned. The Port's redevelopment plans include re-alignment of the entrance road over a portion of the Site. 2.3 HYDROGEOLOGIC SETTING Previous investigations at the Site have advanced ten borings and installed four monitor wells. Five borings (133, B4, B6, B7, B10) and the four monitor wells (MW-1 through MW-4) extend to approximately 10 feet bgs. Four borings (B1, B2, B5, B8, B9) were advanced to approximately 19 feet bgs. The following conceptual model of the hydrogeologic setting has been developed based on the boring logs, excavation records, and depth to ground water. 2.3.1 Local Geology Based on the geologic logs obtained from the soil borings and monitor wells installed at the Site, three geologic cross-sections were constructed at the location shown on Figure 4. Cross- sections A-A', B-B', and C-C' are depicted on Figures 5, 6, and 7, respectively. The boring logs and cross-sections reveal the geologic materials beneath the Site dominated by sandy fill in the upper 4 feet to 5 feet. In addition, sandy fill material is present in the UST excavation area to approximately 11 feet bgs. Because this shallow sandy fill extends beyond Environmental Risk Services,Corp.