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On April 26 and 27, 1990, IT oversaw the installation of four groundwater monitoring wells (MW- 1 through MW-4) at the site. The wells were installed at 30 feet bgs. With the exception of minor concentrations of benzene and ethylbenzene in a 20-foot sample from boring MW-3, soil samples did not contain detectable concentrations of petroleum hydrocarbons. Groundwater samples from wells MWA and MW-3 contained maximum concentrations of total petroleum hydrocarbons as gasoline (TPHg) and benzene at 0.20 parts per million (ppm) and 0.033 ppm, respectively. The direction of groundwater flow was established toward the northeast (IT, Site Assessment Report, dated June 1990). In February and March 1991, IT oversaw the removal of two 10,000-gallon unleaded gasoline USTs, one 10,000-gallon leaded gasoline UST, three 3,000-gallon motor oil USTs, and one 3,000-gallon used-oil UST, associated piping, and the installation of replacement USTs in a new excavation as part of the renovation of the facility. The former USTs were of single-walled construction. These replacement USTs are currently in use at the site. The excavated USTs were in good condition, with the exception of some corrosion noted on the oil USTs. TPHg and benzene were detected at concentrations up to 3,500 milligrams per kilogram (mg/kg) and 3.6 mg/kg, respectively, in samples from the former fuel UST excavation. The highest concentrations of petroleum hydrocarbons were detected along the southwestern portion of the former fuel UST excavation. TPHg and benzene were also present in soil from the product piping excavations at maximum respective concentrations of 677 mg/kg and 2.4 mg/kg. With the exception of a concentration of total petroleum hydrocarbons as diesel (TPHd; 29 mg/kg), petroleum hydrocarbons were not detected in soil from the fuel oil UST excavation. Soil from the new excavation also did not contain petroleum hydrocarbons. Groundwater was not encountered in the former and new UST excavations. Approximately 600 cubic yards of impacted soil were removed from the former gasoline UST excavation and former product piping areas; approximately 800 cubic yards of uncontaminated soil were removed from the new UST excavation; and approximately 350 cubic yards of uncontaminated soil were removed from the former oil USTs. Since well MW-2 was located in the area of the proposed new UST excavation, it was properly destroyed in February 1991 with the oversight of the SJCEHD (IT, 6W Underground Storage Tank Closure Report data April 1991). Soil vapor extraction (SVE) piping, consisting of four-inch diameter perforated casing was installed within the pea gravel backfill at the base of the former fuel UST excavation along the east wall for future remediation of impacted soil (IT, Interim Assessment Report, dated December 5, 1991). Between April and July, 1991, IT oversaw the installation of three monitoring wells (MW-5 through MW-7) completed between 40 feet and 45 ft bgs, two SVE wells (VW-1 and VW-2) completed at a depth of 30 feet bgs, and the installation of a soil vapor collection system at the site. Soil samples did not contain petroleum hydrocarbons, except for TPHg in the 20-foot samples from borings MW-7 and VW-2 (550 ppm) and a relatively minor concentration of benzene in MW-7. Petroleum hydrocarbons were not detected in groundwater samples except for relatively minor concentrations of TPHg in well MW-7. (IT, Interim Assessment Report, dated October 1991). In January 1992, IT conducted a SVE pilot test using the horizontal piping within the former UST excavation, vadose-zone wells, and existing monitoring wells at the site. The SVE test was conducted over a six-hour period on January 21, 1992. Results of the SVE test indicated that a 100-standard cubic feet per minute (scfm) air flow rate was sufficient to achieve an 85 foot radius of influence (IT, Soil Extraction Pilot Test, dated March 1992). 6W L 2 76 Service Station No.11192 Cardno ATC Project Number 52.75118.2390 Stockton,California May 1,2014 6-1