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23 April 2002 <br /> AGE-NC Project No 95-0142 <br /> Page 4 of 16 <br /> Since the approval of the CAP in December 1995,the local and regional ground water elevation has <br />' risen significantly(20 feet)and has maintained a depth-to-water of approximately 25 feet bsg AGE <br /> believes that the sustained increase of ground water elevation has significantly decreased the <br />' potential effectiveness of the proposed SVE/IAS method as a stand alone treatment for impacted soil <br /> and ground water, due to a reduction in thickness of the impacted vadose zone and an increase in <br /> thickness, and volume,of impacted soil(and ground water)in the saturated zone The impacted soil <br />' is primarily fine grained, which may make the upward and lateral path of sparged air through the <br /> saturated zone unpredictable and stripped hydrocarbons unrecoverable <br /> The vertical extent of hydrocarbon-impacted soil had not been fully assessed when the CAP was <br /> developed The mass of adsorbed hydrocarbons now known to be within the saturated zone is <br /> significant,recent evaluation of soil and ground water below 50 feet bsg has documented significant <br /> concentrations of dissolved and adsorbed hydrocarbons that must be satisfactory mitigated to achieve <br /> site closure <br /> At the present time,dissolved hydrocarbon concentrations are known to extend to 80 feet bsg,where <br /> low concentrations suggest that 80 feet bsg is close to the dissolved plume's vertical extent The <br /> anticipated limited overall effectiveness and reliability of 1AS technology to remediate the impacted <br /> lie soil and ground water require a re-evaluation of this proposed method <br /> AGE conducted a ground water extraction pumping test on 18 October 2001 Analysis of the ground <br />' water extraction data indicted that ex-situ ground water treatment was feasible, the radius of <br /> influence generated by a pumping rate of five gallons per minute was interpreted to be adequate to <br /> control further off-site migration of contaminants toward the east, in the predominantly down- <br /> gi'adient direction The results of the pumping tests were reported in the AGE-prepared Ground <br /> Water Extraction Pilot Test Report dated 31 January 2002 <br /> The January 2002 report stated that the soil at the site has a high percentage of fine-grained matrix <br /> and overall is homogenous and mostly fine-grained In general this soil type has a high adsorption <br />' capacity and low permeability, and thereby could potentially limit migration of dissolved <br /> hydrocarbons However,despite the fine-grained nature of the soil,the feasibility test results showed <br /> that ground water extraction should be effective on the site The ground water extraction rates during <br /> full-scale remediation are not likely to exceed the pilot test extraction rate(five gallons per minute), <br /> and may be less for effective ground water extraction and stabilized drawdown <br /> In the report, AGE recommended the use of ground water extraction as an alternative ground water <br /> remediation technique at the site Ground water extraction should provide adequate capture of the <br /> dissolved hydrocarbons, based on site-specific hydrogeologic conditions and hydrocarbon <br />' distribution The limited areal distribution of high concentrations of dissolved hydrocarbons near the <br />' Advanced CeoEnvironmental,Inc <br /> 1 <br />