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rt s the replacement fuel piping The results of compliance soil sample analysis detected up to • 3500 milligrams per kilogram (mg/kg) total petroleum hydrocarbons as gasoline (TPH-G) and 3 6 mg/kg benzene The locations of these soil samples are shown on Figure 4, and the results of soil sample analysis are summarized in Z able 1 Three additional groundwater monitoring wells, MW-5, MW-6 and MW-7, and two vadose zone wells,VW-1 and VW-2,were installed onsite in April and July 1991 Petroleum hydrocarbons were detected only irn the samples collected from Borings MW-7 and VW-2 at concentrations of up to 550 mg/kg TPH-G and 0 7 mg/kg in VW-2 at a depth of 11 feet Groundwater samples were collected in August 1991,but not from Wells MW-1 through MW-4 since they had been dry since May 1990 During that sampling event, petroleum hydrocarbons were only detected rn Well MW-7 at 70 ug/l TPH-G and 19 ug/1 benzene The groundwater gradient was interpreted to be 0 005 in a northerly direction (IT, 1991) In February 1992,grab groundwater sampling was attempted at 11 locations designated THP-1 through THP-1 using a drill rig equipped with a HydroPunch groundwater sampling device Samples could only be collected at three locations,however,with petroleum hydrocarbons detected at concentrations of up to 380 ug/1 TPH-G and 8 4 ug/1 benzene (IT, 1992a) On January 21, 1992, a soil vapor extraction pilot test was performed by using a horizontal perforated piping installed in the former underground fuel tank cavity and monitoring influent using the groundwater monitoring wells The horizontal piping consists of 4-inch- diameter, perforated casing installed along the east wall of the former tank cavity,with a solid riser to the surface During the testing, soil vapor was extracted at a rate of up to 93 standard cubic feet per minute with the vacuum pressure in the monitoring wells ranging from 0 62 inches of water column (in WC) in a well 30 feet from the center of the tank cavity to 0 01 un WC in a well 110 feet away Analysis of soil vapor samples collected during the pilot testing detected up to 2900 milligrams per cubic meter of soil vapor (IT, 1992b) Since installation of the groundwater monitoring wells, groundwater samples have been collected on a quarterly basis Groundwater gradient direction has consistently been in a northerly direction and,since April 1995, all groundwater has been observed in all seven monitoring wells Since the October 1995 sampling event, groundwater samples were additionally analyzed for methyl tert-butyl ether (MTBE) During the most recent groundwater sampling event in January 2001, dissolved-phase petroleum hydrocarbons were detected in samples collected from each of the morutoring wells at a concentration of up to 70000 ug/1 TPH-G, 14 4 ug/l benzene, and 111000 ug/l MTBE 2.12 Source Removal/Abatement Activities completed at the site to remove the source of petroleum hydrocarbons to the soil and groundwater and to remediate residual petroleum hydrocarbons in the subsurface have included the following • Removal of three underground fuel tanks and associated backfill in February 1991 and replacement with tanks in a different location • Removal of three motor oil tanks and one used oil tank and associated backfill material F\00\10-037\ciosedoc 2