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1 l 15 February 2000 AGE-NC Protect No 98-0448 ` ' Page 25 of 33 ' 9 1 3 Monitoring Activities One of the potential problems associated with air sparging is lateral spreading of the contaminant ' plume This can be caused by either mounding of ground water above irilection points or Iatetal air flow away from sparging wells To detect this problem, ground water elevations in monitoring wells and extraction wells (if appropriate) should be monitored on a monthly basis, at the minimum, to ' detect mounding and the presence of organic vapor ' 9 1 4 Feasibility In-situ air sparging of dissolved hydrocarbons in ground water at the site has a moderate to high ' feasibility at the site Based on data collected during the 1AS feasibility pilot, conditions at the site are conducive for air sparging activity Remediation of ground water at the site would require only a moderate number of infection and extraction points and utilization of a small area for an underground injection/extraction piping network Air infection and extraction rates must be balanced to prevent tfie Mimed migration of contaminants Based on the guide How to Evaluate Alternative Cleanup Technologies For UST Sites (October 1994) published by the United States Environmental Protection Agency(EPA) Office of USTs, LAS ' is generally effective when permeability rates are greater than 10-9 (Exhibit VII-11) Results of the laboratory analysis indicated that permeability conditions at the site are adequate for air sparging activity Soil in the saturated zone between twenty and thirty-five feet and forty-five and ray feet has a moderate amount of sand content, potentially making IAS effective for this zone Figures 5 and 6 ' depict cross sections, showing subsurface soil types at the site An IAS pilot test was performed at the site, results of the pilot test are summarized in Section 4 0 ' A concern with IA.S is precipitation of iron and/or manganese,which can cause clogging of sparging points Laboratory analysis of iron at the site indicated that iron concentrations in ground water at the site are adequate for IAS Another concern with IAS could be air flow channeling between the ' bottom sand interval and the intermediate silt/clay'interval However, a balanced spacing of SVE wells screened through the silty/clay interval should alleviate any air flow channeling 1 915 Duration ' Air sparging in moderately permeable aquifers generally result in remediation rates comparable with soil vapor extraction rates At the site, we estimate a remediation period of 12 to 24 months for Advanced CeoEnvironmental,Inc f