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• I• SITE HISTORY In March 1998, Quik Stop Markets replaced three underground fuel tanks at the subject site At the time of the tank removal, it appeared petroleum hydrocarbons had impacted the native sand at the capillary fringe of the water table During the tank removal, groundwater was encountered at approximately 15 feet below the ground surface and had been impacted by petroleum hydrocarbons Upon removal of the fuel tanks,the pea-gravel in the excavation did not visibly appear to have been impacted by the hydrocarbons Six soil samples collected from the bottom of the excavation (approximately 14 to 15 feet)were reported to be relatively free of detectable TPHg/BTEX compounds These six soil samples were, however, found to contain varying concentrations of methyl-t-butyl-ether (MTBE), ranging from 43 micrograms per kilogram (ug/kg) to 27,000 ug/kg Two grab water samples collected from the excavation indicated that groundwater beneath the fuel tanks had been impacted with petroleum hydrocarbons Over-excavating the remaining pea-gravel and capillary fringe area was impractical, since further excavation of the pea-gravel and some of the native sand would have seriously Jeopardized the canopy and could have undermined the stability of the two nearby streets, Union Road and West Louise Avenue, as well as an historical marker, which is located on the northwest corner of Union Road and West Louise Avenue Based upon this data, Quik Stop prevented further collapse within the excavation and supported the canopy footing by back-filling the excavation with the stockpiled pea-gravel Since the stockpiled material was • virtually free of petroleum contamination, it was Quik Stop's and Compliance & Closure, Inc (CCI)'s opinions that using the stockpiled pea-gravel would not add to any groundwater contamination that may exist at the site Further environmental work was necessary to define the extent of soil and groundwater contamination in the area of the fuel tanks In October 1998, CCI conducted a Soil and Groundwater Investigation at the subject site using a Geoprobe direct push sampling rig A total of twenty-one soil samples and five grab water samples were collected for chemical analysts during the investigation Laboratory analysis of the soil and groundwater samples collected from the site during this investigation revealed only one (GP-1) area, on the north side of the site, to contain petroleum hydrocarbons This area was reported to contain the highest levels of petroleum compounds (27,000 ug/kg MTBE) dunng the fuel tank removal in March 1998 Three monitoring wells were installed at the site in April 1999 and quarterly groundwater monitoring was initiated On January 20, 2000, CCI conducted the first quarterly monitoring at Quik Stop Market No 121 Groundwater samples collected from the three on-site wells in January were reported by the laboratory to contain elevated concentrations of methyl tertiary butyl ether(MTBE) The three wells were reported to have MTBE concentrations of 59 micrograms per liter(ug/L) in well MW-2, 21,000 ug/L in well MW-1 and 58,000 ug/L in well MW-3 These samples were analyzed using EPA Test Method 8020 In order to confirm the MTBE concentrations, CCI re-sampled the three wells on February 17, 2000 During the re-sampling of the wells,monitoring well MW-3 had a moderate product odor No odor was noted in the other two wells The three water samples