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The UST was removed by ATC on March 4, 1999. The UST and/or the piping system associated with the UST appeared to have released petroleum hydrocarbon product into the soil on site. Stained and odorous soil was observed in soil samples collected from the base of the UST excavation. The UST excavation area soil had a maximum detected concentration of total petroleum hydrocarbons — diesel fuel (TPH-D) at the south end of the UST at 4,900 milligrams per liter (mg/L) at a depth of 16 feet bgs (the maximum depth of the excavation). Elevated TPH- D concentrations were also found in the west and southwest ends of the excavation. Benzene, toluene, ethylbenzene, and total xylenes (BTEX) and methyl tert butyl ether (MTBE) were not detected in the UST excavation area soil. A soil boring investigation by ATC, described in a report dated April 6, 2000, found that diesel impacted soil appears to be confined to the immediate vicinity of the former UST excavation in an area of approximately 25 feet long by 25 feet wide. Analytical results of groundwater samples indicate that diesel fuel in the groundwater has migrated from the former UST excavation to the south and east. The diesel fuel impacted groundwater appeared to be laterally confined to an area approximately 60 feet long by 35 feet wide. Diesel fuel was found at a maximum reported concentration of 150 micrograms per liter (ug/L) adjacent to the UST excavation, and attenuated to a concentration of 58 ug/L, 20 feet farther to the south. No BTEX or MTBE was detected in the groundwater samples collected from the borings, with the exception of total xylenes detected in the sample from one boring at 1.2 ug/L. REMEDIAL ACTION SUMMARY Following removal of the UST, approximately 371 tons of diesel fuel-impacted soil were removed from the site and disposed at the BFI Landfill located in Livermore, California on March 23, 1999. The UST excavation was backfilled with clean soil imported to the site. SCOPE OF WORK Project Objective: The primary objectives of this site investigation will be to install three wells to a depth of 38 feet below ground surface (bgs) on site. Quarterly groundwater monitoring and sampling will be conducted for a period of one year. The results of the proposed plan will be the basis for potential site closure, or additional action, if required. This Workplan addresses the tasks involved in successfully implementing the site investigation. These key tasks include: Utility Location, Health and Safety, Well Installation Permitting, Well Installation, Field Sampling and Analysis, Data Management, and Reporting. Each key task is described below. Utility Location An ATC geologist will mark the locations of the proposed boreholes, and contact Underground Service Alert (USA) which will provide clearance so that no public underground utilities will be disturbed. A private utility locator will also be used to clear underground utilities. The site owner or ATC Associates Inc. 2 75.75128.0001