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• Mr Nuel Henderson,Jr, SJCPHS July 1, 2003 Remedial Action Plan ARCO Station No 6100 Page 2 complex The product piping lines and dispensers were upgraded in February 2002 The site is approximately 300 feet above mean sea level (msl) with topography sloping towards the southeast The area surrounding the property is undeveloped land BACKGROUND Site background information presented here is based on review of various reports prepared by Roux Associates, Resna, IT Group, and Delta Environmental Consultants, Inc (Delta) During November 1990 and February 1991, Roux Associates oversaw excavation and removal of five USTs and associated product lines Based on visual evidence of contamination in the old and new tank cavity, aver-excavation was conducted in November 1990 A total of 29 soil samples were collected from the over-excavated pit along the sidewalls and bottom of the excavation The soil sampling locations and analytical results of soil samples collected during the UST removal and piping upgrade are presented in Appendix A During the soil investigation studies conducted between October 1991, and December 1995, a total of 31 soil borings, ranging in depth from 26 to 116 feet below ground surface (bgs), were drilled, 20 of the borings were completed as vapor extraction wells VW-1 through VW-20 Groundwater was not encountered during any of these investigations Concentrations of total petroleum hydrocarbons as gasoline (TPHG), and benzene, toluene, ethylbenzene, and total xylenes (BTEX) were detected 1n soil from 6 to 115 feet bgs, with the highest concentrations identified at approximately 26 to 45 feet bgs Tabulated analytical results for soil samples collected during site assessment studies are presented in Appendix B In October 1991, Resna conducted a soil vapor extraction pilot test using wells VW-1 through VW-4 During the test, influent vapor concentrations as TPHG ranged from 130,000 mg/m3 and 160,000 mg/m3 An average radius of influence of 35 feet was estimated during this test In October 1998, Pinnacle Environmental Solutions, Inc submitted Hydrocarbon Mass Evaluation, presenting the estimated mass of TPHG and BTEX constituents An addendum to this report was prepared by the IT Group and submitted in September 1999 San Joaquin County Public Health Services (SJCPHS) submitted a Case Closure Summary to the California Regional Water Quality Control Board (CRWQCB) on February 1, 2000, requesting "no further action" of environmental work at the site CRWQCB declined the request for no further action (March 14, 2000) and required that a groundwater investigation be conducted at the site P 1Bp-Arco for UR5161001Reports\Arco 6100 RAP doe