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5.2 Lateral Extent of Vadose-zone Contamination Several soil-vapor samples collected by Evax Technologies in 1990 detected vadose- zone contamination in the vicinity of the dispenser island, but vadose contamination was not confit med by soil samples from borings B2, B3, and B4 in 1992 None of the six Evax soil-vapor samples nearest the tank cavity detected contamination, but relatively low concentrations of hydrocarbons were encountered in vadose samples ' from MW-2, near the western edge of the tank cavity Contamination within the vadose zone is thus lunited to the area west of B1, B2, and B4 and north of the former dispenser islands (Figures 3 and 5) This area measures 30 feet in length by ' 20 feet in width by approximately 5 feet in thickness, and occupies roughly 100 cubic yards The two soil samples collected and analyzed from this area (MW2-25 and MW2-30) average 15 mg/kg for all BTE&X compounds combined and 5 5 mg/kg for ' TPH 5.3 Lateral Extent of Saturated-zone Contamination ' As noted in section 5 1 contamination is more extensive within the saturated zone ne ' than within the vadose zone Of the three groundwater samples collected so far, the highest concentrations were detected in MW-2 TPH concentrations are also elevated in MW-1 Only benzene has been detected in MW-3, and at a much lower concentration than in the other wells Contamination was also detected in soil w samples at and below the soil/water interface in boring B3 and monitoring wells MW-1 and MW-2 No contamination was detected in soil samples from the capillary fringe zone in borings B2, B4, B5, and B5 in'the first phase of drilling, but no samples were collected from the saturated zone The present data are insufficient to define the lateral extent of contamination within the saturated zone 5.4 Recommendations ' I ' The presence of benzene and other hydrocarbons within the saturated zone and in groundwater precludes closure of this site by the regulatory agencies at this time The fairly extensive contamination plume: within the saturated zone, relative to ' contamination in the vadose zone, and the enrichment of TPH-g and the heavier aromatic compounds (xylene and ethylbenzene) relative to benzene and toluene in some samples, indicate that the contamination is old This is consistent with the fact ' that the unauthorized release occurred prior to 1980,when the UST's were removed ll ' It`therefore appears unlikely that the contamination w111 degrade naturally to ,`,'acceptable levelsi quickly I GeoAudrt recommends that'the wells Ibe monitored monthly,for the nelxtl quarter to s verify i the groundwater flow directioln The next I sampllmg event should occur, in II ' Marche 1994; and should,be repeated on a quarterly,!basis thereafter,lto monitor any < changeslin the direction of groundwater flow due to, seasonal variations. I 1 t 0e41.1r 1 A.&S...w I.. �.,.ey�wnA+nsa 12