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• 19 July 2004 , <br />AGE -NC Project No 95-0121 <br />' Page 9 of 9 <br />Besides HU1 and HU2, AGE has identified a deeper hydrogeologic flow unit (HU4-Second Flow <br />' Uniti at depths between 40 and 53 feet bsg Based on petroleum concentrations encountered <br />i <br />previously in water samples collected in this interval from wells MW -1 through MW -4, MW -7 and <br />based on the `grab' ground water samples collected from CPT -2, corrective action is warranted <br />within HU4-Second Flow Unit (40 feet to 53 feet bsg) in the area between these wells However, due <br />to (1) the slow pace and marginal effectiveness of IAS currently being encountered within HU1 and ' <br />HU2, and (2) the unfavorable lithology changes between HU1, HU3 and HU5 (less permeable silts <br />and clays) and HU2 and HU4 (more permeable fine to medium sand),1AS will probably not be the <br />best feasible remediation alternative to address HU4 because of the high potential for air flow <br />' channeling Figure 3 shows a geologic cross section (A -A') that depicts the hydrogeologic units <br />Based on the well-defined, laterally continuous, sandy nature of HU4, it would appear advantageous <br />' to compare (feasibility study) both a ground water pump -and -treat and ozone sparging technologies <br />screened through HU4 (40 to 60 feet), implementation of an additional ground water remediation . <br />technology would be used to remediate HU4 ground water impact as well as augment the IAS clean- <br />' up efforts in HU1 and HU2 <br />_ r I <br />• 5.0. LIMITATIONS I <br />' Our professional services were performed using that degree of care and skill ordinarily exercised by <br />environmental consultants practicing in this or similar localities The findings were based mainly , <br />upon analytical results provided by an independent laboratory Evaluations of the <br />geologic/hydro-geologic conditions at the site for the purpose of this investigation are made from a limited number' <br />of available data points (CPT data, soil samples and `grab' ground water samples), and subsurface <br />conditions may vary away from these data points No other warranty, expressed or implied, is made <br />' as to the professional recommendations contained in this report <br />I <br />I <br />f <br />, <br />_ , J <br />Advanced GeoEnvironmental, Inc L <br />S I� <br />7 <br />~ 7 <br />