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E s <br /> ! 15 November 1995 <br /> I AGE-NC Project No 95-0142 <br /> Page 14 of 19 <br /> bsg Considering the clay-rich soil at the site, we estimate that these wells could create a cone of <br /> I' influence of approximately 20 to 25 feet under adequate vacuum The IAS system must be combined <br /> with vapor extraction to contain vapor stripped from the ground water <br /> 7 1 3 MONITORING ACTIVITIES <br /> I <br /> One of the potential problems associated with air sparging is lateral spreading of the contaminant <br /> I plume This is due either to mounding of ground water above injection points or lateral air flow away <br /> from sparging wells To detect this problem, ground water elevations in monitoring wells and <br /> extraction wells (if appropriate) should be monitored on a monthly basis (minimum) to detect <br />' mounding and organic vapors <br />' 714 FEASIBILITY <br /> Remediation of large ground water plumes require the installation of many injection and extraction <br /> wells Air injection and extraction rates must be balanced to prevent the forced migration of <br /> contaminants Extensive piping must be installed to injection and extraction wells As in vapor <br /> extraction, air spargmg is not effective in the remediation of longer-chain hydrocarbons <br /> 715 DURATION <br />' Air s ar n highly permeable aquifers generally results in rapid reduction of hydrocarbon <br /> p l� g in g i <br /> concentrations in the saturated zone However, based upon the overall lower permeability of soil at <br />' the site (clayey), IAS will probably proceed more slowly <br /> Pilot tests have not been conducted at this site, but remediation periods are commonly thought to be <br /> comparable with soil vapor extraction durations Based upon dissolved hydrocarbon concentrations <br /> currently present in ground water at the site and experience at other sites, we estimate a remediation <br /> period of 24 to 30 months <br /> 7 2 GROUND WATER EXTRACTION <br /> 7 2 1 BASIC PRINCIPLES <br /> s <br /> There are several different methods for treatment of extracted ground water, which are collectively <br /> called "pump and treat" As the name indicates, all methods involve extraction and transfer of <br /> Icontaminated ground water from the aquifer to an above-ground treatment or disposal/recycling <br />