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� I � Ms Margaret Lagorio • Page 6 of 8 The concentration of MTBE was 24,000 ppb TPHg was detected at a concentration of 110,000 ppb, ' benzene was detected at 29,000 ppb, toluene was detected at 880 ppb ethylbenzene was detected at 1,000 and xylenes were detected at 2,500 ppb Groundwater analytical results are sununanzed in Table 2 Laboratory reports end chain of custody documentation are included in Attachment C 1 CONCLUSIONS Vadose Soil ' Results from confirmation soil samples collected within and along the perimeter of the former tank pit indicate successful remediation of vadose zone soils has occurred as a result of previous operation of the soil vapor extraction system The only residual contaminated soil in the vadose zone, in the area of boring CB3, does not appear to be amenable to further vapor extraction inasmuch as the contaminant is depleted in the more volatile and toxic components and is bound up within an impermeable silty clay t Soil results from currently saturated soils in borings CB 1, CB3 and CB4 reflect the influence of operation of the soil vapor extraction system during penods when water levels were lower than at present Depth to water is currently about 38 feet below grade When vapor extraction began in the fall of 1997, depth to '. water was approximately 48 feet below grade Soil samples collected from these bonngs indicate no sigrtificant soil contamination is currently present at 40 and 50 feet and only minor levels exist at 55 feet Vertical Extent of Soil Contamination The vertical extent of//S-Oil contamination has been defined Contamination of any significance does not ' exceed a depth of 107 feet bgs, where only trace levels of TPHg and BTEX are present Traces of toluene and xylenes reported in the samples collected from 112 and 125 feet and the trace levels of TPHg and BTEX in the sample collected from 135 feet are postulated to have resulted from cross contamination of the ' sampling equipment Regardless or whether or not this is the case, the contaminant levels in these deep samples are inconsequential ' Soil contamination of significance is concentrated within the depth interval of approximately 65 to 85 feet Within this impacted interval, TPHg averages less than 1,000 ppm in the sandy lithologies As would be expected, the silt encountered at 80 feet has a greater hydrocarbon sorption capacity and the TPHg ' concentration in this lithologic unit was over 10,000 ppm This unit and the underlying silty clay has apparently served to limit deeper transport of significant levels of hydrocarbons ' Vertical Extent of Groundwater Contamination The vertical extent of significant groundwater contamination does not exceed 140 feet bgs, where only trace ' levels of BTEX compounds were detected For practical purposes, the vertical limit of significant groundwater contamination probably does not extend any great distance beneath 115/120 feet The sample collected at 112 feet had reported concentrations of TPHg and BTEX three orders of magnitude less than the ' sample collected at 88 feet RodcYlonnskmlhaup.Aoa