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. SITE HISTORY CANEPA'S CAR WASH 6230 Pacific Ave. Stockton, CA Canepa's Car Wash consists of an automated car washing facility, a fuel station and a convenience store. The site is located at 6230 Pacific Avenue, in Stockton, California. The car wash and fuel station has been in operation for over two decades. Between February 25 and.March 3, 1993, three underground storage tanks (USTs), fuel lines and dispensers were removed by WHF Environmental (WHF) and replaced with a doubled walled system. The USTs consisted of two 12,000-gallon gasoline USTs and one 5,000-gallon diesel UST. As reported by WHF, upon removal of the tanks and piping, it was discovered that the fuel lines had leaked and that the USTs had been overfilled. Approximately 600 cubic yards of soil were removed from the UST excavation area. The excavated soil was subsequently characterized and disposed of at Forward Landfill in Manteca, California. At least 16 soil samples were collected from the tank excavation for laboratory analyses. The laboratory results indicated predominantly low TPH-G (gasoline at <15 mg/kg) and low BTEX concentrations. One (1)soil sample collected from the northeastern sidewall of the tank excavation contained 773 mg/kg TPH-G and BTEX concentrations up to 170,000 mg/kg (total xylenes). TPH-D (diesel) was detected in one soil sample at 32 mg/kg. At least seven soil samples were collected from beneath the former fuel dispenser islands for laboratory analyses. Elevated concentrations of TPH-G (up to 3,800 mg/kg) and BTEX concentrations ranging from 26 mg/kg to 560,000 mg/kg were detected in the fuel dispenser soil samples. TPH-D (diesel) was not detected at or above the laboratory reported detection limit in the soil samples collected from beneath the former fuel dispenser islands_ On March 12, 1993, soil boring (B-1)was installed by WHF immediately east of the former fuel dispenser islands. Groundwater was encountered at approximately 56 feet below the ground surface (bgs). Moderate to strong petroleum odors were detected from 15 feet bgs to 56.5 feet bgs. Elevated TPH-G and BTEX concentrations were detected in soil samples collected from 35 feet bgs to 56.5 feet bgs. Following the soil boring installation, a network of nine SVE wells were drilled and installed in the area of the fuel dispenser islands. According to the former consultant, William H. Fox of WHF, the SVE wells were installed without compiling geological logs and without the collection of laboratory samples as agreed upon by the PHS/EHD, due to time constraints. Mr. Fox indicated that based on field observations, all of the SVE wells showed signs of gasoline contamination during installation. An internal combustion unit (ICU)was installed at the site for vapor extraction and treatment under the Authority to Construct issued by the San Joaquin Valley Unified Air Pollution Control District (APCD), dated October 7, 1993. The ICU was started on March 11, 1994, and operated through June 10, 1995. Based on field monitoring notes prGVidcd by WiT, average influent organic vapor concentrations, mcasurcd with a photo ionization detector(PID), exceeded 2,200 parts per million (ppm). The last influent measurement collected from the system was 2,145 ppm (May 15, 1995). Between September 28 and 30, 1993, WHF installed four(4) monitoring wells (MW-1 through MW-4) at the site. Low to elevated concentrations of gasoline were detected in groundwater samples collected from MW-1 through MW-4. Field observations indicated moderate to strong gasoline odors in the soil at MW-1 from 20 feet to 55 feet bgs and at MW-2 from 40 feet to 67 feet bgs. Soil samples collected from MW-1 and MW-2 were not analyzed in the laboratory. Analyses of soil analyses of samples collected from MW-3 and MW-4 indicated that TPH-G or BTEX were not detected at or above the laboratory reported detection