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• Well Installation and Site Investigation Report ARCO Facility No.5469 Stockton,California Page 2 owner east of the ARCO Station have been unsuccessful. Stratus will continue to pursue access to this property. SITE DESCRIPTION The site is located in a mixed commercial and residential neighborhood on the cast side of Wilson Way, approximately 200 feet north of Highway 4, in Stockton, California. Gasoline is dispensed from three 10,000-gallon underground storage tanks (USTs) and two dispenser islands located in the southwest corner of the property. The location of site facilities are shown on Figure 2. Motor vehicle fuels have also been released to the subsurface from the properties immediately north (Knowles property, 102 Wilson Way) and west (former Top Filling Station, 101 Wilson Way) of the ARCO site. SITE BACKGROUND In February 1999, The IT Group (IT) observed the removal and replacement of product lines and associated dispensers. Samples collected in the vicinity of the dispenser islands indicated the presence of total petroleum hydrocarbons as gasoline (TPHG) at concentrations up to 7.32 milligrams per kilogram (mg/kg), benzene at a concentration of m tert-but 1 alcohol TBA at 44 mg/kg, and meth l-tert butyl ether MTBE 0.187 mg/kg, y (TBA) g g� Y Y (MTBE) up to 5.16 mg/kg (IT, 2000). Based on the analytical results, limited excavation of hydrocarbon impacted soil was performed in the vicinity of the north end of the two dispenser islands. Approximately four cubic yards of impacted soil was excavated from the north end of the western dispenser island. Due to subsurface utilities and native hardpan soils (encountered at approximately three feet below ground surface [bgs]), only overlying pea-gravel was hand excavated from the north end of the eastern dispenser island. Approximately 60 cubic yards of soil and pea-gravel were excavated and removed from the site (IT, February 2000). Between June 5, and June 8, 2000, Delta oversaw Woodward Drilling Company of Rio Vista, California, drill and install six groundwater monitoring wells (MW-1 through MW-6). The wells were constructed of 4-inch diameter, 0.020-inch factory-slotted PVC casing from a depth of approximately 33 to 53 feet bgs. The site was subsequently placed on a quarterly monitoring program. In response to the PHS/EHD request for additional assessment to evaluate lateral and vertical impact of petroleum hydrocarbons to soil and groundwater, Delta oversaw Woodward Drilling Company install four additional monitoring wells (MW-7 through MW-10) on May 30, and May 31, 2001. The wells were constructed using 4-inch diameter, 0.020-inch factory slotted PVC casing installed to a depth of approximately 33 to 53 feet bgs (MW-7 & MW-8), and approximately 59 to 74 feet bgs (MW-9 and P:1Bp-Arco For URS154691Reports15469report2D03.doe