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01 June 1999 <br /> AGE-NC Project No 95-0137 <br /> Page 19 of 26 <br /> i <br /> infection rate Only slight ground water mounding was observed during the sparging test Data from j <br /> ' the air sparging pilot test are included in Appendix D <br /> A potential concern with air sparging is precipitation of iron, which can cause clogging of sparging <br /> points Laboratory analysis of water samples indicated low concentrations of iron in water at the site, <br /> indicating minimal concern for iron precipitation <br /> t <br /> 616 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 site,we estimate a remediation period of 12 to 24 months for shorter-chain <br /> hydrocarbons Longer-chain (diesel)hydrocarbons, detected in water samples collected at the site, <br /> ' will probably require longer remediation periods If ground water remains at its current elevation, <br /> impacted silt within the upper saturated zone may slow overall site remediation and hinder extraction <br /> of volatilized hydrocarbons <br /> 6 1 7 Cost <br /> tInstallation 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 $20,000 to <br /> ' $40,000 Sparging equipment maintenance and monitoring would range from $5,000 to $10,000 <br /> 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 /> tvapor extraction estimates <br /> ' 6 2 GROUND WATER EXTRACTION <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 /> contaminated ground water from the aquifer to an above-ground treatment or disposal/recycling <br /> facility The extraction is performed using an automatic pump system to maintain capture <br /> ' characteristics in the aquifer and to assure that process volume requirements are maintained After <br /> treatment,the water is usually discharged into a sanitary sewer,however,a sanitary sewer connection <br /> is not readily available at the site <br /> Advanced GeoEnvironmentai,Inc <br />