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EXECUTIVE SUMMARY • Condor Earth Technologies, Inc. (Condor) prepared this combination Problem Assessment Report(PAR)/ Corrective Action Plan (CAP) to summarize the investigation of the release of petroleum hydrocarbons to soil and groundwater, and to evaluate remedial alternatives for mitigation, at Canepa's Car Wash, 6230 Pacific Avenue, Stockton, California. The business consists of an automated car washing facility, a fuel station, and a convenience store. In 1993, three underground storage tanks (USTs) were removed. Soil samples indicated subsurface contamination, and four monitoring wells were installed. Nine SVE wells were installed and a thermal oxidation unit was installed at the site for vapor extraction and treatment from March 1994 through June 1995, and with modifications again from 1999 to the present. Since 1993 multiple investigations have essentially defined the lateral and vertical extent of subsurface contamination. Quarterly monitoring of the groundwater monitoring wells is continuing. In general, organic clay is present from the surface to about eight feet. Beneath the clay to a depth of about 50 to 60 feet are silt deposits with interbedded and discontinuous lenses of clayey to silty sand. Below approximately 60 feet, sands are more abundant. Groundwater beneath the site is unconfined and the depth to the water table in June of 2002 was about 35 feet. The overall trend in groundwater table elevation is downward from 1950 to at least the mid sixties. From 1994 to the second quarter of 2000, the trend was upward with a rise of about 20 feet at the site. Since second quarter 2000, the elevation has been relatively flat with a seasonal range of about 2 feet. • Soil contamination resulting from the release was detected in samples collected from depths ranging from about 26 feet to 70 feet. Presumably as a result of the soil vapor extraction system, a recent investigation indicate virtually no soil contamination exists above groundwater table. The groundwater plume is generally confined to the site. Conservatively, the plume contains an estimated 372,000 cubic feet of groundwater and 6.7 gallons of benzene. The Risk Based Corrective Action Evaluation was conducted using benzene as the constituent of greatest ' concern. The Average Inhalation Exposure Concentration (vapor intrusion into on-site buildings) was calculated to be 0.024 milligrams per cubic meter (mg/rn). This is in comparison to the Occupational Safety and Health Administration limit of 3.25 mg/m3, or the National Institute for Occupational Safety and Health recommended limit of 0.325 mg/m3. However, this also would produce an individual cancer risk of 2.0 in 10,000, greater than the target level of one in one million. ' Evaluation of the remedial alternatives for soil and groundwater at the site is complicated because of saturation of the contaminated soil by the 20-foot rise in the elevation of the water table. Due to the depth of the soil contamination (below the groundwater, more that 30 feet deep) excavation and ex situ treatment of the soil is not possible. Also, because of the urban location and congested use of the site, very 'little space is available for ex situ treatment units. Consequently, alternatives considered included: 1. In situ attenuation through passive biodegradation; 2. Enhanced in situ bioremediation and/or chemical oxidation; 3. Soil Vapor Extraction; 4. Air Sparging; . 5. Ex situ groundwater treatment(pump and treat); and 6. Combinations of Alternatives 2 through 5. I.L ' �a CONDOR