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11 February 2003 <br /> AGE-NC Project No. 98-0520 <br /> ' Page 16 of 21 ; <br /> ' 7.2.3. Monitoring Activities <br /> One of the potential problems associated with air sparging is lateral spreading of the contaminant <br /> plume. This can be caused by either mounding of grouild water above injection points or lateral air <br /> flow away from sparging wells:To detect this problem,ground water elevations in monitoring wells <br /> and extraction wells (if appropriate) should be monitored on a monthly basis, at the minimum, to <br /> detect mounding and the presence of organic vapor. <br /> 7.2.4. Feasibility <br /> Air-sparge testing has not been performed at the site.Remediation of small dissolved ground water <br /> plumes requires the installation of a few injection and extraction wells.An extensive piping network <br /> for injection and extraction must also be installed. Air.injection and extraction rates must be <br /> balanced to prevent the forced migration of contaminants. In addition, a concern with air sparging . <br /> is precipitation of iron, which can cause clogging of sparging points. However, air sparging has <br /> proven itself as a very effective method for remediation of soil in the smear zone. <br /> 7.2.5. Duration <br /> ' Air sparging in highly permeable aquifers generally results in rapid reduction of hydrocarbon <br /> concentrations-in the saturated zone. Remediation times are generally comparable with soil vapor <br /> extraction times.At the subject site,we estimate a remediation period of 12 to 24 months for shorter- <br /> 'chain hydrocarbons. Longer-chairs (diesel) hydrocarbons have been detected in water samples <br /> collected at the site, and will require longer remediation periods. If ground water'remains at its <br /> ' current elevation; the impacted clayey silt within the upper saturated zone may slow overall site <br /> remediation andhinder extraction of volatilized hydrocarbons. <br /> ' '7.2.6. Cost <br /> ' Installation of an in-situ air sparging system will require the installation of several sparging and <br /> extraction wells,piping system and equipment. Setup costs would likely range from $10,000.00 to <br /> $15,000.00. Sparging equipment maintenance and monitoring would range from $5,000.00 to <br /> ' $10,000.00 annually. <br /> If air sparging is chosen for ground water remediation,vapor extraction will be used for vadose zone <br /> soil remediation.Therefore,extraction equipment and monitoring costs would be included under soil <br /> vapor extraction estimates. <br /> 1 <br /> Advanced GeoEnvironmental,Inc. <br />