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U Ms. Lori Duncan,REHS Page 2 of 8 San Joaquin Environmental Health Department June 9,2005 of vertically into the proposed vapor extraction wells, URS proposes that sparging be limited to the silt zone above this silty sand layer. This will prevent the sparged air from entering the sandy zone and possibly pushing the impacts laterally. SITE BACKGROUND The site is on the northeastern comer of West Charter Way and Lincoln Street in Stockton, California, as shown on the site location map (Figure 1). The site is currently vacant and paved with asphalt. There are no site buildings or underground storage tanks (USTs) on the property. The current property owner is planning to construct a car wash at the site(Figure 2). Previous Investigations ARCO Station 2168 operated until 1995. Between July 1991 and October 1993, twenty-one soil borings were drilled at the site; 7 were converted to groundwater monitoring wells (MW-1 through MW-7) and 7 were converted to vapor extraction wells (VW-1 through VW-7). Between May 1995 and July 1996 six additional vapor extraction wells were installed (VW-8 through VW-13), and between July and August 2000, five additional groundwater-monitoring wells were installed at the site(MW-1B,MW-1C, MW-8,MW-8B, and MW-8C). Seven current and former UST facilities are in the site vicinity, and a laterally extensive co-mingled dissolved petroleum hydrocarbon plume presently encompasses the site. In May 1995, EMCON prepared an off-site evaluation report identifying four potential upgradient/off-site sources of contamination to the ARCO site. These sources are the: Texaco Service Station at 440 West Charter Way; Chevron Service Station at 508 West Charter Way; Transmission Store at 515 West Charter Way; and Shell Service Station at 620 West Charter Way. Two non-oil company responsible parties are south of the Texaco property, and a possible additional responsible party (the City of Stockton Corporation Yard) is south of the Chevron property. All of these responsible parties are upgradient from the site and have impacted groundwater. UST removal activities were conducted in 1986 and 1996. An underground waste oil tank was formerly located in the northeastern corner of the site. The waste oil tank was reportedly removed on November 18, 1986. Two 6,000-gallon single-walled steel USTs, one 8,000-gallon single-walled steel UST, and one 10,000-gallon single-walled fiberglass UST and associated product piping and dispensers were removed in February 1996. Locations of the former USTs are shown on Figure 2. Following UST removal, the facility was demolished. The USTs most recently contained regular, mid-grade, and supreme unleaded gasoline.Historically, the site has dispensed regular and premium leaded gasoline. KAWproeessU5 BP ARCO\02168\2005 System Installation\SVE-AS WorkplanAm