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URS <br /> FjMs. Lori Duncan,REHS <br /> Page 2 of 6 <br /> San Joaquin Environmental Health Department <br /> j November 15, 2006 <br /> I <br /> Fj Previous Investigations <br /> ARCO Station 2168 operated as a retail fuel station until 1995. Between July 1991 and October 1993, <br /> F1twenty-one soil borings were drilled at the site; 7 were converted to groundwater monitoring wells <br /> (MW-1 through MW-7) and 7 were converted to vapor extraction wells (VW-1 through VW-7). <br /> Between May 1995 and July 1996 six additional vapor extraction wells were installed (VW-8 through <br /> VW-13). Between Jul August 2000 five additional F Y and Ag groundwater-monitoring wells were installed at <br /> the site (MW-1B,MW-IC,MW-8, MW-8B, and MW-8C). <br /> UST removal activities were conducted in 1986 sand 1996. An underground waste oil tank was formerly <br /> located in the northeastern corner of the site. The waste oil tank was reportedly removed on November <br /> F1 18, 1986. Two 6,000-gallon sin single-walled g ed steel USTs, one 8,000-gallon single-walled steel UST, and <br /> one 10,000-gallon single-walled fiberglass UST and associated product piping and dispensers were <br /> removed in February 1996. Following UST removal, the facility was demolished. The USTs most <br /> recently contained regular, mid-grade, and supreme unleaded <br /> �' p gasoline. Historically, the site has <br /> dispensed regular and premium leaded gasoline. <br /> Fil SoiI Remediation <br /> Approximately 300 cubic yards of hydrocarbon-impacted soil were removed from the site during the <br /> UST- and dispenser-removal activities. SVE was conducted from January 1997 through February 1998 <br /> f • to remediate vadose zone soil impacts. SVE was terminated after an estimated mass of approximately <br /> 10,000 pounds (approximately 1,600 gallons) of total petroleum hydrocarbons as gasoline (TPHg) was <br /> removed and influent benzene concentrations were less than laboratory reporting limits of 0.5 milligram <br /> { per cubic meter(mg/m3). <br /> Groundwater Monitoring <br /> The site has been on a quarterly groundwater monitoring schedule since February 1995. Groundwater <br /> concentrations during the first quarter 2005 included gasoline range organics (GRO) up to 29,000 <br /> micrograms per liter(gg/L) (MW-4),benzene up to 12,000 pg/L (MW-4), and methyl tert-butyl ether up <br /> to 23 pg/L (MW-1). Groundwater is currently approximately 20 feet below the ground surface (bgs) and <br /> flowing in an easterly direction. <br /> F; CONSTRUCTION ACTIVITIES <br /> The following paragraphs present a discussion of drilling and well installation, the subsurface <br /> F conditions encountered, well sampling and surveying, soil analytical data, groundwater analytical data, <br /> _ soil and wastewater disposal, and treatments system installation. <br /> i K:1WprocessV5 BP ARCO\0216512006 System Instal lation\Report.doc <br />