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0 <br /> 0 <br /> lie 23 May 2003 <br /> AGE-NC Project No 95-0184 <br />' Page 8 of 9 - <br />' 4 0. SUMMARY AND CONCLUSIONS <br /> Based on the findings from this Investigation, supplemented with data from previous site <br />' investigations, AGE concludes <br /> • The subsurface stratigraphy in the southern portion of the site is composed predominantly <br /> of interbedded fine-grained soil,mainly clay, silty clay,clayey silt and silt Interbedded sand <br />' layers generally appear as fine-grained or cemented,laterally discontinuous layers which may <br /> be more prevalent and coarser with depth Based on CPT-generated lithologic properties, <br /> AGE identified a vadose zone extending from surface grade to approximately 35 feet bsg and <br />' fourteen hydrologic units Five hydrologic units(HU5,HU7 and HU9,HUI I and HU13)are <br /> sand-bearing units of low dynamic pore pressures, the remaining units are predominantly <br /> zones of interbedded clayey silt, silty clay, clay and stiff fine-grained sediment, with <br />' occasional, laterally discontinuous sand lenses, pore pressures within these intervals vary <br /> from low to high <br />' Vertically,the highest petroleum hydrocarbon-impacted CPT water samples were collected <br /> from fine-grained soil intervals between approximately 50 and 85 feet bsg (HU2 and HU3) <br /> • and between 135 and 160 feet bsg (HU12) at the southern tanks location (CPT-2), the <br />' impacted ground water plume extends laterally at all depths to the CPT-3 location(Figures <br /> 4 to 6) <br />' • BTEX compounds'were detected at all depths in the CPT bonngs With the exception of <br /> HU5, BTEX in water samples collected from CPT-2 exceeded the DHS's Maximum <br /> Contaminant Levels (MCLS) for BTEX in ground water, benzene was the only BTEX <br />' compounds exceeding the MCL in water samples collected from CPT-3 <br /> • GVOCs were detected at all depths in the CPT borings 1,2-DCA was present in HU2 and <br />' HU 12/13 at concentrations exceeding the MCL In addition,naphthalene,n-propyl benzene, <br /> 1,2,4-trimethylbenzene and 1,3,5-tnmethylbenzene concentrations in HU3 and HU12/13 <br /> exceeded their respective action levels, and n-propyl benzene exceeded its action level In' <br />' HU2 <br /> • The vertical and lateral extent of contaminated soil and ground water have not been defined <br />' at the site <br />' 5.0. RECOMMENDATIONS <br /> Based on the findings from this investigation, AGE recommends <br />' Continued quarterly ground water monitoring, the next monitoring event is scheduled for <br /> June 2002 <br /> tAdvanced GeoEnvironmental,Inc <br /> 1 <br />