SITE INFORMATION AND CORRESPONDENCE

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Emcon 1433 North Market Boulevard • Sacramento,California 95834-1943 • (916)928-3300• Fax(916)928-3341 EXECUTIVE SUMMARY ARCO Service Station 2168 441 Charter Way,Stockton, California BACKGROUND Since 1991 to the present, ARCO has conducted subsurface investigations to evaluate if petroleum hydrocarbons have impacted soil and groundwater. The investigation included drilling 23 soil borings and installing five onsite monitoring wells, two offsite monitoring wells; and nine onsite vapor extraction wells. Based on analytical results of soil samples collected from the borings, hydrocarbons were detected in soil in the historical capillary fringe zone (from 25 to 40 feet below ground surface). Results of groundwater samples indicated dissolved hydrocarbons are present in groundwater. The highest dissolved hydrocarbon concentrations were detected in the upgradient and offsite monitoring wells. Based on information supplied by ARCO, the waste oil tank was removed on November 18, 1986. PROPOSED WORK As part of ARCO divestment of the site, ARCO will remove four underground storage tanks at the site: two 6,000-gallon tanks and two 8,000-gallon tanks. EMCON (Environmental Consulting Firm) will oversee the removal of these tanks. The general scope of work will consist of the following: • Collect appropriate soil samples within 2 to 4 feet below the base of the former gasoline tanks. One soil sample will be collected from beneath each end of each UST for a total of 8 soil samples. • Collect and analyze one soil sample every 20 linear feet below the former product lines. Up to seven soil samples will be collected from beneath the product lines. • Observe additional excavation in the gasoline-tank cavity, dispenser islands, product delivery lines and in the area where 5 gallons of gasoline were released from a fractured product line, if field evidence indicates hydrocarbons remain in place. EMCON may excavate until (1) field screening data (using a photoionization detector [PID]) of soil samples collected from the base and sidewalls of the excavated area indicate soil containing relatively high concentrations of hydrocarbons have been removed, or (2) the safe operating limits of the equipment are reached. • Soil generated from the removal of the tanks will be stored onsite, and placed on and covered with plastic. A composite sample (four soil samples) will be collected from every 100 cubic yards of soil generated. The samples will be composited by the laboratory and analyzed for petroleum hydrocarbons. In addition, soil collected from the stockpiled soil generated from the soil beneath the leaded gasoline UST will be analyzed for total lead. Results of analyses of samples collected from the soil will be used by ARCO's contractors to evaluate disposal options. If results of soil samples collected from the stockpiled soil are relatively high, EMCON will aerate the stockpiled soil onsite.