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CLEARWATER ' G R O U P Environmental Seroiees plume is located in the area of well MW-5B, and extends back to the former UST pit Future soil ' remediation efforts at the site would best be directed at this area as it appears to be acting as a significant source of ongoing groundwater contamination 3.4 Dissolved-Phase Contamination Results of cumulative investigation efforts indicate that the dissolved-phase contaminant plume ' is generally limited to the dimensions of the subject property, however it is migrating southeast in the direction of groundwater flow The area containing high concentrations of dissolved-phase ' contaminants is mainly limited to the vicinity of the core of soil contamination Concentrations of dissolved-phase TPHg and benzene in this location (MW-5B) were recently 3,100 µg/L and ' 120 ttg/L, respectively Although some residual sorbed-phase contamination appears to be present in the southeast corner of the former UST bed, dissolved-phase contaminants are ' significantly less in this area (MW-1) This indicates that the residual sorbed-phase contamination in the area of MW-5B is likely an ongoing source of dissolved-phase lie contamination The core of the plume is located proximal to the former UST pit and MW-5 The maximum ' extent of the residual dissolved-phase contaminant plume is on the order of 275 feet long (parallel to groundwater flow) and 150 feet wide (perpendicular to groundwater flow) Based on 1 the approximate plume dimensions noted above and the assumption of plume thickness of 15 feet and porosity of saturated zone of 0 35, it is estimated that approximately 1,125,435 gallons of groundwater are affected by gasoline contamination It estimated that on the order of 3 to 5 gallons of gasoline reside in the dissolved-phase beneath the site The great disparity between mass of contaminants in the sorbed- and dissolved-phase is typical of many gasoline ' contaminated sites 1 1 • ZB178C RAP 15 May l8,2004 1