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StatusReport ARCO Facility No 6100 Tracy, California Page 2 • sample the onsite water supply well (modify wellhead for appropriate sampling if needed) on a quarterly basis, and • pursue offsite access to private property south of the site It was also concluded that Delta should reevaluate information gathered from previous investigations conducted at the site regarding the subsurface conditions (soil stratigraphy, distribution of hydrocarbons, etc ) to aid in developing an approach to further characterize the site Additionally, the locations of the water supply wells identified in the DWR well survey should be field verified The results or status of the additional activities performed in the first quarter 2001 are presented in the following sections A work plan outlining the proposed scope of work for further assessment is currently being prepared and will be submitted within the next 30 days In addition to characterizing the hydrogeology and the extent of liquid-phase hydrocarbons, the work plan will address onsite characterization of oxygenates recently identified in water samples collected from selected vapor extraction wells An access agreement has also been recently sent to the owner of the property located immediately south of the site • SITE BACKGROUND The site is currently an active ARCO service station located at the northwestern corner of the intersection of Patterson Pass Road and Interstate 580 near Tracy, California The facility configuration is shown on Figure 2 The site is approximately 300 feet above mean sea level (rnsl) with topography sloping towards the southeast The area surrounding the property is undeveloped land Originally one 550 gallon waste oil underground storage tank (UST), one 10,000-gallon gasoline UST and four 6,000-gallon USTs were present at the site The waste oil tank was removed in 1987 From November 1990 to February 1991, the five USTs and associated product delivery lines were removed and replaced with four 10,000-gallon USTs Soil investigations were conducted between 1991 and 1995 Concentrations of total petroleum hydrocarbons as gasoline (TPHG) and benzene, toluene, ethylbenzene, and total xylenes (BTEX) were detected in soil from 6 to 115 feet bgs, with the highest concentrations identified at approximately 26 to 45 feet below ground surface (bgs) A total of 31 soil borings, ranging in depth from 26 to 115 feet bgs, were drilled, 20 of the borings were completed as vapor extraction wells Groundwater was not encountered during any of the investigations • A water supply well was installed onsite in 1969 in the southwestern corner of the property and currently supplies water to the service station The well was constructed of