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Ms.Lori Duncan Page 3 of 9 San Joaquin County Environmental Health Department August 25,2004 In February 1998,four gasoline USTs of various capacities and their associated piping were removed. Soil samples indicated that soil was impacted with TPHg and benzene in the area of the USTs. Soil sample locations and analytical results are summarized in Appendix D. In October 1998, a dual completion SVE well (VW-5S and VW-5D)and three AS wells (AS-1, AS-2, and AS-3)were installed. Soil samples collected at this time confirmed the presence of hydrocarbon-impacted soils in the vicinity of the USTs. Maximum concentrations of TPHg and 1 benzene were 7,830 mg/kg and 11.5 mg/kg,respectively. Well locations are shown in Figure 2 and analytical results are presented in Appendix E. An SVE/AS system involving 6 SVE wells(VW-1 through VW-4, VW-5S and VW-5D)and three 1 AS wells(AS-1 through AS-3) began operating in September 2000. The system was operated almost continuously through June 2004. Low influent concentrations prompted the shutdown of the SVE system in June 2004. To date, the SVE system has removed approximately 2,000 lbs of petroleum hydrocarbons from the subsurface. In addition, 7 gallons (43.17 lbs) of free product have been removed from site wells (Table 2). SVE/AS system performance evaluation data are presented in Appendix F. Local Groundwater Use In July 2004, URS reviewed well records files at the Department of Water Resources(DWR). General well information and production well information was reviewed for wells within a radius of 2,000 feet from the site. DWR records identified 12 domestic wells and 2 public groundwater production wells within that radius. Table 3 summarizes well details,and Appendix G presents DWR well completion reports for the wells. City of Stockton Public Works Department(CSPWD) was contacted for information regarding the construction details, locations, and production data for any wells within that radius. CSPWD identified one production well within that radius. The production well is City Well# 1 (Well ID #13 in Table 3 and Figure 1), approximately 950 feet south-southeast of the site. This well produces approximately 800 gallons per minute(gpm)and is screened at various intervals between 170 and 240 feet bgs. CSPWD located no other municipal production wells within the search area. z Sensitise Receptors In July 2004,URS conducted a walking and driving reconnaissance sensitive receptor survey to �4 identify all potential receptors within a 500-foot radius of the site. No surface water bodies,child care centers, schools, or wildlife habitats were identified within 500 feet during this survey. However, URS did identify two elementary schools within 2,000 feet of the site. Colonial Heights �i School is 1,000 feet to the northwest, and Carden School is 1,800 feet to the east. The nearest surface water body is Fivemile Slough, 2,200 feet southeast of the site. Figure 1 shows the locations of the schools and creek. KAWprocess1J5 BP ARCOU54812004 SCM\Site Conceptual Model V2.doc