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ARCO station 548 C O R 1612 West Hammer Lane,Stockton Remedial Action Plan May 31,2006 2.0 SITE BACKGROUND 2.1 Site Description The site is located at the southwest corner of West Hammer Lane and Brentwood Drive in the City of Stockton, California (Figure 1). The site was formerly operated as an ARCO Service Station and AM/PM mini-mart. The site currently operates as a Valero gasoline service station and mini-mart. Current site facilities include four underground storage tanks (LISTS); two pump islands, associated product lines anddispensers, and a convenience store. 2.2 Previous investigations Various phases of environmental assessment are summarized below. Locations of sample points and wells are shown on Figure 2. A table summarizing the well construction details is included as Table 1. Boring logs and well construction details are presented in Appendix B. Historical soil analytical data are presented in Appendix C. Historical groundwater analytical figures are presented in Appendix D. Site Investigations began in October 1990 with five soil borings (B-1 through B-5) located around the USTs and product lines. Soil samples were collected and analyzed for petroleum hydrocarbons including total petroleum hydrocarbons as gasoline (TPHg) and benzene. Hydrocarbons were detected in six of the 18 samples collected. The highest concentrations detected were 1,400 milligram per kilogram (mg/kg) for TPHg and 1.2 mg/kg for benzene. These detections were located in samples around the USTs at 30 feet and 40 feet, respectively. The investigation concluded that hydrocarbon impacted soil was limited to the proximity of the UST complex. Results of this sampling are included in Appendix C. In October 1991, four on-site groundwater monitoring wells (MW-1 through MW-4), and three soil vapor extraction (SVE) wells (VW-1, VW-2, and VW-3) were installed. Soil samples collected identified maximum TPHg and benzene concentrations of 340 mg/kg and 0.031 mg/kg, respectively. These results also indicated that petroleum hydrocarbon impacted soil was limited to the area of the UST complex. In 1992, RESNA conducted an SVE test at the site. The test concluded that the site soil could be mitigated by SVE, with each well having a radius of influence of 30 feet. In 1993, two additional monitoring wells (MW-5 and MW-6) and one SVE well (VW-4) were installed. Soil samples did not contain detectible amounts of TPHg. One sample from B-15 (near the dispensers) had concentrations of benzene reported at 0.024 mg/kg. During the drilling of boring B-18, a product line was accidentally fractured, resulting in the release of product into the soil. VW-4 was installed adjacent to B-18, for future mitigation of the released product. In 1994, EMCON conducted a site evaluation for prioritization of remediation efforts at ARCO sites in San Joaquin County. EMCON calculated approximately 383 pounds (lbs) of total petroleum hydrocarbons at the site (URS, 2005a). I:IBP-ARC0104 BP valley Portfolio15481Reports\RAP1548 RAP.doc 2