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Levels in MW-2 increased slightly- benzene from 0 5 to 4 0 ug/L; <br /> toluene from ND to 10 0 ug/L; ethylbenzene from 0 . 6 to 1 . 0 ug/L, <br /> xylene from 0 4 to 8 0 ug/L; and TPHg from 079 to 110 mg/L <br /> MTBE was not present <br /> Levels in MW-3 changed as follows benzene decreased from 479 to <br /> 103 ug/L; toluene increased from 6 . 0 to 12 0 ug/L; ethylbenzene <br /> decreased from 153 to 18 0 ug/L, xylene increased from 10 0 to <br /> 36 . 0 ug/L; and TPHg decreased from 2 67 to 0 910 mg/L. MTBE was <br /> detected at 8 0 ug/L, it had not been analyzed in prior events <br /> Both MW-4 & MW-5 were below detection levels for all compounds . <br /> 4 PLATES II through VI show the estimated lines of equal <br /> concentration of benzene, ethylbenzene, toluene, xylene, & TPHg <br /> based on the latest test results . They reveal that the center of <br /> the plume is in the vicinity of MW-1, which has been confirmed by <br /> prior work The shape of the plume has not changed significantly <br /> since monitoring began, indicating that it has stabilized <br /> CONCLUSIONS - <br /> 1 The limits of the soil & water plumes have been defined in <br /> all directions There is no indication of an offsite source <br /> 2 The groundwater plume has migrated no more than 100 feet to <br /> the north and 125 feet to the west of the site of UST' s, which <br /> were removed in 1989 The highest levels of BTEX & TPHg have <br /> consistently been recorded from MW-1, indicating that there has <br /> been very little movement of the groundwater <br /> 3 Because the highest levels of contamination in both the soil <br /> and groundwater have been in the area of MW-1 and the north pump <br /> island, there is a good possibility that leaking product lines <br /> and/or the fuel dispensers on the north island contributed to the <br /> soil & water contamination <br /> RECOMMENDATIONS : <br /> 1 It is recommended that sampling of MW-4 and MW-5 be discon- <br /> tinued They have not recorded any contamination during the last <br /> two sampling events <br /> 2 We propose that a soil boring be placed in the center of the <br /> north dispenser island to determine if that area was a mayor <br /> source of contamination Soil samples taken at 51 , 101 , & 15 ' <br /> Should be sufficient to characterize that area The samples <br />. would be analyzed for BTEX, TPHg, & MTBE If the results of that <br /> work are definitive, it may be more cost effective to remove <br /> 2 <br />