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I 19 June 2001 AGE-NC Project No 97-0326 ' Page 6 of 7 4.0. SUMMARY AND CONCLUSIONS ' The implications of the February 2001 CPT investigation results are as follows ' The more permeable lithology encountered during the CPT investigation consists of laterally discontinuous lenses of fine to coarse sand at depths between 19 and 24 feet bsg and at approximately 34 feet bsg in the western portion of the site, a continuous sand layer at a depth ' between78 and 80 feet bsg, and silty to gravelly sand in CPT-03 at a depth of 110 feet bsg Variable lithology including silty fine sand and sandy silt was encountered at a depth between 14 to 19 feet ' bsg overlying the sand lenge in the western portion of the site Less-permeable fine grained lithology (clay, silty clay and clayey silt) characterizes the remaining subsurface sediment ' AGE interprets the CPT data to identify four hydrostratigraphic units(HSUs)at the site The second and fourth HSUs are sandy and potentially high permeability flow units with significant lateral continuity The first and third HSUs are fine grained intervals, possibly leaky confining layers, ' through which the contaminates of interest can apparently migrate TPH-g and various BTEX compounds were detected in all HSUs,laterallythe highest concentrations were centered around the tank-pit area (CPT-01) in HSU-2 and HSU-3, but TPH-g, benzene and ethylbenzene concentrations were slightly higher off-site at CPT-03 m HSU-1 compared to CPT-01 In addition, three other analytes (isopropylbenzene, n-propyl benzene and 1,1,2-trichloroethane) ' detected in HSU-1,which were common to on-site and off-site CPT locations,were present at higher concentrations in the off-site CPT location No lateral trend could be determined for HSU-4,where only one ground water sample was collected ' The vertical concentration profiles of TPH-g and BTEX compounds on-site in the HSUs generally exhibited decreasing concentrations with increasing depth, within HSU-1 the off-site CPT-03 ' location had contamination levels that increased by an order of magnitude between the top of HSU-1 (110 µg/1 TPH-g)to near the base(4,900 µg/1 TPH-g) of HSU-1 In HSU-3, low concentrations of ' petroleum hydrocarbon compounds were still detectable in the ground water sample from CPT-01, but none were detected in samples from the other CPT locations However,increased concentrations of TPH-g and BTEX compounds were detected again in the underlying HSU-4 at off-site CPT-03, 1 suggesting that the contaminants may have migrated through the less impermeable layer between approximately 60 to 100 feet bsg (lower portion of HSU-1 and HSU-2 and HSU-3) or might have originated from an unidentified off-site source Advanced GeoEnvlronmental,Inc