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S E C O R Work Plan for Soil Vapor Survey August 9, 2007 ARCO Service Station No. 2186 Page 2 of 8 kilogram (mg/kg) in B-1 at 56.5 feet below ground surface (bgs) and B-3 at 56.5 feet bgs to 3.3 mg/kg in B-3 at 41.5 feet bgs. Benzene was detected in borings B-1 and B-3 at concentrations of 0.015 mg/kg in B-3 at 56.5 feet bgs to 0.019 mg/kg in B-1 at 56.5 feet bgs. GRO and benzene, toluene, ethylbenzene, and xylenes (BTEX) concentrations were below laboratory detection limits for the other soil samples analyzed. From June through July 1999, two 10,000-gallon and one 8,000-gallon double-walled fiberglass UST's, associated dispensers, and piping was removed from the site. Two 20,000-gallon UST's were installed in the same cavity as the former USTs. Pinnacle Environmental Consultants (Pinnacle) of Cameron Park, California, conducted compliance soil sampling activities for the tank pull. Analysis of compliance soil samples indicated that GRO, benzene, and methyl tertiary butyl ether (MTBE) contamination were present in the soil. The excavation areas were backfilled with pea gravel. Soil sample results indicate that petroleum hydrocarbon impacts are distributed in the northern and southwestern areas of the former gasoline UST complex (T-1-S, T-1-N, T-2-N, and T-3-N) at depths of 17 to 18 feet bgs. Detected GRO concentrations ranged from 240 to 11,000 mg/kg. Soil samples collected from the central-southern and southeastern corner of the former UST complex did not contain GRO at concentrations exceeding method reporting limits (MRL's) (T-2- S, and T-3-S). Sidewall samples from the northern and-western ends of the UST excavation (SW-N and SW-W) contained GRO at concentrations of 364 and 1,840 mg/kg, respectively. Benzene was detected in one soil sample in the northeastern corner of the UST excavation at a concentration of 0.19 mg/kg (T-3-N). Benzene was also detected in sidewall sample SW-N at a concentration of 0.545 mg/kg. All other UST excavation samples did not contain benzene at concentrations exceeding MRL's. MTBE was detected in all six of the UST excavation samples. In addition, all four of the sidewall samples contained concentrations of MTBE above MRL's. UST excavation samples contained concentrations of MTBE ranging from 9.2 to 272 mg/kg. The northwestern corner sample (T-1-N) contained the highest MTBE concentration. Sidewall samples contained concentrations of MTBE ranging from 0.221 to 23.8 mg/kg. A Sidewall soil sample taken from the northern wall of the UST excavation (SW-N) contained the highest concentration of MTBE. Piping and dispenser samples generally contained low non-detectable concentrations of toluene and total xylenes. With the exception of sample P-6, GRO and benzene were not detected. MTBE concentrations ranged from 0.114 to 33.2 mg/kg. Limited overexcavation was conducted in two localized areas beneath piping trenches and dispensers due high photo ionization detector (PID) readings. Soil samples taken from the over excavated locations were taken at seven feet bgs. Soil samples collected from the former product delivery piping (PL-6), in the vicinity of the former tank pit area, contained detected GRO concentrations 7,040 mg/kg. Soil and fill material removed from the UST complex and piping trenches (SP-1) were characterized and removed from the site by Dillard Trucking, Incorporated for disposal at BFI Landfill, Vasco Road, Livermore, California. Excavation backfilling activities were completed on July 19, 1999, and the former UST complex, dispenser areas, and product delivery piping areas were resurfaced. In August 1999 International Technology Corporation (IT) of Cameron Park, California, conducted a soil and groundwater assessment that included two cone penetrometer test (CPT) 2186 SVI 8-07.doc SECQR International Incorporated