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ARCO Station 548 c C O R 1612 West Hammer Lane,Stockton .3 Remedial Action Plan May 31,2006 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. Results are included in Appendix C. In October 1998, a dual completion SVE well (VW-5S and VW-50) and three air sparge (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 benzene were 7,830 mg/kg and 11.5 mg/kg, respectively. An SVE/AS system utilizing six SVE wells (VW-1 through VW-4, VW-5S and VW-5D) and three air sparge wells (AS-1 through AS-3) began operation in September 2000. The system was operated nearly continuously until June 2004. Low influent concentrations prompted the shutdown of the SVE system in June 2004. The SVE system removed approximately 2,100 lbs of petroleum hydrocarbons from the subsurface. In addition, seven gallons (43.17 lbs) of free product were removed from site wells during this time. In December 2004, two groundwater monitoring wells (MW-7 and MW-8) were installed to monitor the lateral and vertical extent of groundwater impacts at the site. MW-7 is located off site and down gradient of the former USTs and MW-8 was installed in the vicinity of the former USTs to monitor deep groundwater. TPHg, benzene, toluene, ethylbenzene, and xylenes were reported in soil samples from MW-8. No detections were found in MW-7. Currently all groundwater monitoring, vapor, and air sparge wells are sampled quarterly. . 2.3 Sensitive Receptor Survey As requested, a sensitive receptor survey was performed as a part of this RAP. According to the Environmental Data Resources Inc (EDR) database sensitive receptor survey report, there are twenty nine (29) water wells located within a one-mile radius of the site (EDR, March 23, 2006). Two of these wells are located within a quarter mile of the site. This report can be found in Appendix E. Table 2 summarizes the wells found in the survey. According to the Geotracker database (www.geotracker.swrcb.ca.gov) there are four water supply wells located in the vicinity of the site at an unknown distance. Two wells are owned by the City of Stockton and the other two wells are owned by the County of San Joaquin. In July 2004, URS Corporation (URS) conducted a file review at the Department of Water Resources (DWR) and City of Stockton Public Works Department (CSPWD) to identify wells within a radius of 2,000 feet from the site and a sensitive receptor survey to identify all potential receptors within a 500-foot radius. DWR records identified 12 domestic wells and two public groundwater production wells within a 2,000-foot radius of the site. CSPWD identified one active production well within the 2,000-foot radius. The production well is City Well # 1, located 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 below ground surface (bgs). The sensitive receptor survey did not identify any surface water bodies, child-care centers, schools, or wildlife habitats within 500 feet of the site. I:1BP-ARC0104 BP Valley Portfolio15481ReportslRAP1548 RAP.doc 3