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Mr Nuel Henderson, SJCEHD April 7, 2006 <br /> 40Well Installation Report <br /> ARCO Facility No 5469 <br /> Stockton,California <br /> Page 2 <br /> Motor vehicle fuels were also released to the subsurface at the Knowles-Roek property, <br /> situated immediately north of the site at 102 South Wilson Way, and at the former Top <br /> Filling Station, situated immediately northwest of the site at 101 South Wilson Way <br /> SJCEHD is also directing environmental oversight cases relating to underground fuel <br /> releases at both of these properties Figure 3 illustrates the location and general <br /> configuration of the Knowles-Rock property and the former Top Filling Station property <br /> BACKGROUND <br /> In February 1999, The IT Group (IT) observed the removal and replacement of product <br /> lines and associated dispensers Samples collected in the vicinity of the dispenser islands <br /> indicated the presence of total petroleum hydrocarbons as gasoline (TPHG), benzene, <br /> methyl tertiary butyl ether (MTBE), and tertiary butyl alcohol (TBA) at maximum <br /> concentrations of 9 18 milligrams per kilogram (mg/Kg), 0 187 mg/Kg, 11 I mg/Kg, and <br /> 44 mg/Kg, respectively (IT, February 2000) <br /> IT directed a limited excavation in order to remove petroleum hydrocarbon impacted soil <br /> from beneath the northern end of the two dispenser islands Approximately 4 cubic yards <br /> of impacted soil was excavated from the north end of the western dispenser island Due <br /> to subsurface utilities and native hardpan soils (encountered at approximately 3 feet <br /> below ground surface [bgs]), only overlying pea-gravel was hand excavated from the <br /> north end of the eastern dispenser island Approximately 60 cubic yards of soil and pea- <br /> gravel generated during site renovation activities were excavated and removed from the <br /> site (IT, February 2000) <br /> Delta Environmental Consultants, Inc (Delta) directed the installation of six on-site <br /> groundwater monitoring wells (MW-1 through MW-6) in June 2000 The site was <br /> subsequently placed on a quarterly monitoring program Delta directed the installation of <br /> four additional groundwater monitoring wells (MW-7 through MW-10) in May 2001, as <br /> requested by SJCEHD <br /> Delta also oversaw the installation of five ozone infection wells (IW-1 through IW-5) in <br /> March 2002 Stratus directed the advancement of one cone penetrometer test (CPT) <br /> boring on-site in November 2002 Table 1 summarizes information regarding historical <br /> soil boring and well constructions at the site <br /> Stratus has been operating and maintaining an ozone infection in-situ groundwater <br /> remediation system since December 2002 Ozone infection into the saturated zone is <br /> ongoing <br /> •1 <br /> K 1Bp-Arco for URS%54691ReportsWRC05469-wellreport2006 doc 5TRATU5 <br />