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direction of groundwater flow in the shallowest aquifer is generally to the southeast (Cambria, 2007). 2.4 TOPOGRAPHY AND SURFACE WATER The elevation of the Site is approximately 10 feet above mean sea level. The Site is generally flat. Mormon Slough flows generally toward the west and passes within approximately 3,000 feet north of the Site before draining into the Stockton Deep Water Channel and San Joaquin River. Walker Slough flows generally toward the west and passes within approximately 7,000 feet south of the Site before draining into the San Joaquin River. 2.5 UST HISTORY Colombo/Toscana owned and operated two 4,000-gallon gasoline UST systems for fleet refueling at the Site. The USTs (located west of and adjacent to the warehouse building) and the fuel dispenser(located inside the building) were removed for permanent closure in February 1994 (Figure 3). No record is available to confirm whether the associated UST system piping was removed during the closure activities. During the UST removal, the San Joaquin Health District (SJHD) inspector noted three %2-inch diameter holes on the bottom of the southern UST (SJHD, 1994). Following removal, four soil samples were collected from the excavation floor at approximately 13 feet BGS, and one soil sample was collected from the area of the former fuel dispenser at approximately 3 feet BGS. The samples were submitted and analyzed for total petroleum hydrocarbons in the gasoline range (TPH-g), benzene, toluene, ethylbenzene, and xylenes (BTEX), ethylene dibromide (EDB), and total lead. TPH-g was detected in the two soil samples collected from the western end of the excavation at concentrations up to 6,300 milligrams-per-kilogram (mg/kg). TPH-g was not detected in the other soil samples (Secor, 1996). Benzene was detected in one soil sample collected below the eastern end of the southern UST at a concentration of 0.0086 mg/kg. EDB was detected in the two soil samples collected from the western end of the excavation at concentrations up to 0.130 mg/kg. 2.5.1 Summary of Environmental Investigations Environmental investigations were performed at the Site between February 1996 and December 1997. Historical soil analytical data are presented in Tables 1 and 2. Analytical data for grab groundwater samples collected during the investigations are presented in Table 3. Historical sampling locations are presented on Figure 3. The results of these environmental investigations are presented below. February 1996 Subsurface Investigation In February 1996, Secor International Incorporated (Secor) performed a subsurface investigation. Four soil borings were drilled (MW-1, VE-1, SB-1, and SB-2) to total depths 4