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Mr.Nuel Henderson, SJCEHD November 4,2005 Well Installation Work Plan ARCO Station 5469,Stockton,California Page 2 the property and an underground storage tank (UST) complex situated in the west central portion of the property. The configuration of the facility is shown on Figure 2. Properties in the vicinity of the site are primarily developed for commercial use. Motor vehicle fuels were also released to the subsurface at the Knowles-Roek property, situated immediately north of the site at 102 South Wilson Way, and at the former Top Filling Station, situated immediately northwest of the site at 101 South Wilson Way. SJCEHD is also directing environmental oversight cases relating to underground fuel releases at both of these properties. Figure 3 illustrates the location and general configuration of the Knowles-Roek property and the former Top Filling Station property. 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), benzene, methyl-tert butyl ether (MTBE), and tertiary butyl alcohol (TBA) at maximum concentrations of 9.18 milligrams per kilogram (mg/kg), 0.187 mg/kg, 11.1 mg/kg, and 44 mg/kg, respectively (IT, February 2000). IT directed a limited excavation in order to remove petroleum hydrocarbon impacted soil from beneath the northern end of the two dispenser islands. Approximately 4 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 3 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 generated during site renovation activities were excavated and removed from the site (IT, February 2000). Delta Environmental Consultants, Inc. (Delta) directed the installation of six on-site groundwater monitoring wells (MW-1 through MW-6) in June 2000. The site was subsequently placed on a quarterly monitoring program. Delta directed the installation of four additional groundwater monitoring wells (MW-7 through MW-10) in May 2001, as requested by SJCEHD. Delta also oversaw the installation of five ozone injection wells (IW-1 through IW-5) in March 2002. Stratus directed the advancement of one cone penetrometer test (CPT) boring on-site in November 2002. Table 1 summarizes information regarding historical soil boring and well constructions at the site. K:1Bp-Arco for URS154691Work Plans\Arco5469-well install workplan-2005.doc 5TKAM5