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Project No S8100-06-11 A June 29, 1995 A vertical zone of residual benzene in the vadose zone exists in MW-6 between the depths of 6 1 and 16 8 ' meters (20 and 55 feet) bgs with the maximum benzene concentration of 0 12 mg/kg detected in the 13 7 meter (45 foot) sample interval Low concentrations of benzene were detected in MW-7 at 0 005 mg/kg in the 16 8 meter (55 foot) sample interval, and in MW-8 at 0 006 mg/kg in the 15 2 and 16 8 meter (50 ' and 55 foot) sample intervals Residual concentrations of ethylbenzene and total xylenes were detected in vadose zone soil in MW-5 and ' MW-6 Ethylbenzene was detected in MW-5 at the 13 7 meter(45 foot) sample interval at a concentration of 0 013 mg/kg Total xylenes was detected in MW-5 between the depths of 12 2 and 13 7 meters (40 and 45 feet) bgs with a maximum concentration of 0 63 mg/kg in the 13 7 meter(45 foot) sample interval In MW-6, total xylenes was detected between the depths of 12 2 and 13 7 meters (40 and 45 feet) bgs ' with a maximum concentration of 0 12 mg/kg in the 12 2 meter (40 foot) sample interval 43 GROUNDWATER ANALYTICAL RESULTS ' During the site investigation performed by Geocon, groundwater samples were collected from the pre- existing wells, MW-1 through MW-3, the new monitoring wells MW-4 through MW-8, and the vapor ' extraction well VW-1 The groundwater samples collected during the current site investigation were tested for the presence of TPHg, TPHd, and BTEX The results of the most recent groundwater sampling events performed by Geocon are described below rTPHd was detected in VW-1 only at a concentration of 600 ug/L TPHg was detected in MW-1 through MW-8 and VW-1 with concentrations ranging from 130 ug/L to 28,000 ug/L The maximum concentration of 28,000 ug/L was detected in VW-1, located within the former UST excavation The distribution of gasoline range hydrocarbons in groundwater extends beyond ' the existing perimeter monitoring wells The concentrations of BTEX in groundwater can be grouped into two categories The first group of wells MW-1 through MW-3 and VW-1, located in the vicinity of the former fuel USTs and the associated pump islands, and downgradient perimeter well MW-6 and MW-7 contain elevated BTEX concentrations The range of BTEX concentrations is 13 ug/L to 5,300 ug/L benzene, 1 7 ug/L to 2,500 ug/L toluene, 0 7 ug/L to 300 ug/L ethylbenzene, and 4 4 ug/L to 2,000 ug/L total xylenes, respectively ' The second group of wells are the perimeter wells MW-4, MW-5, and MW-8 and they contain low BTEX concentrations near the laboratory reporting limits The range of BTEX concentrations is, <0 5 to ' 3 1 ug/L benzene, 0 6 ug/L to 1 8 ug/L toluene, <0 5 to 0 6 ug/L ethylbenzene, and <0 5 to 7 0 ug/L total xylenes, respectively ' Historical analytical results and analytical results for groundwater samples collected during the site investigation are summarized on Table III Laboratory reports and cham-of custody records are presented in Appendix E 9