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26 July 2002 AGE-NC Project No. 97-0326 Page 2of10 Based on a General Soil Map from the San Joaquin County Soil Survey, published by the United States Department of Agriculture Soil Conservation Service in 1992, the site area is described as within the Jacktone-Hollenbeck-Stockton(JHS)association.The JHS soils are located on basin rims and within basins, and generally consist of somewhat poorly drained and moderately well drained, fine-textured soils that are moderately deep and deep to a cemented hardpan.The JHS soils generally formed in alluvium from mixed rock sources. 2.2. UNDERGROUND STORAGE TANK REMOVAL The three underground storage tanks (USTs) were removed from the site on 13 February 1998. Petroleum hydrocarbons were detected in soil samples collected from below two 12,000-gallon USTs at concentrations as high as 1,400 milligrams per kilogram(mg/kg). Petroleum hydrocarbons were not detected beneath a 1,000-gallon UST. 2.3. PREVIOUS SUBSURFACE INVESTIGATION The following is a brief summary of site assessment activities to date: • On 19 June 1997, four soil probe borings (probings) were advanced at the site near the 12,000-gallon USTs. Three probings were advanced to a vertical depth of 20 feet below surface grade(bsg);due to the presence of hydrocarbon odor,one probing(B2)was advanced to a vertical depth of 45 feet bsg. TPH-g was detected at depths of 30 and 40 feet bsg at concentrations of 460 mg/kg and 1,000 mg/kg, respectively, beneath the south ends of the USTs. Petroleum hydrocarbons were not detected at a depth of 45 feet bsg or in samples analyzed from the three other probings. Soil probe boring installations were described in theAGE-prepared Preliminary Site Assessment Report in August 1997. • One 20,000-gallon UST was installed at the site following the 1998 UST removals. Approximately 341 tons of hydrocarbon-impacted soil were excavated during removal of the old USTs and overexcavation for the installation of the new UST and piping. Soil was disposed at Forward Landfill. During the UST installation, two conductor casings were installed through the pea gravel adjacent to the UST in anticipation of future site assessment need. The UST removal, overexcavation and UST installation were described in the AGE- prepared UST Removal Report, dated 26 May 1998. • Three ground water monitoring wells were installed in December 1998 as part of site assessment activities. Petroleum hydrocarbon-impacted soil was encountered in all well borings. The maximum concentration of TPH-g was 4,200 mg/kg (MW-1). Benzene and MTBE were detected only in soil sample MW2-35 at 0.0058 mg/kg and 0.011 mg/kg, respectively. Advanced GeoEnvironmental,Inc.