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g) Is there evidence that vapors are escaping to undesirable locations? These locations can include buildmgs or utility corridors If the ISAS system is accompanied by a SVE system,refer to the subsurface performance checklist for SVE systems Causes may include unproper operation of the accompanying SVE system,preferred hydrogeologic pathways, other outside sources of contaminants It may be necessary to re-evaluate the site geology to identify stratigraphic control on m)ected air paths, increase SVE extraction rates from certain wells or the entire system,install additional SVE wells m areas of madequate extraction,or re-consider other source removal alternatives h) Is there evidence that water table fluctuations have affected the distribution of air isolated contaminants, or introduced additional contaminants into the treatment zone i) Are increasing infection pressures required to achieve airflow? This may be due to biofoulmg,or siltation of the spargmg wells, or rising water levels Consider well rehabilitation or well replacement 8) Alternatives for Possible Cost Savings a) Has the system reached its cleanup objectives? Determine if the ISAS operation is still necessary or have the concentrations decreased so that the operation can be termmated9 b) If the cleanup objectives have not yet been met, can the system be turned off and natural attenuation be allowed to achieve the cleanup objective while remaining protective of human health and the environment9 (Refer to Air Force protocols for evaluating natural attenuation— Technical Protocol for Evaluating natural Attenuation of Chlorinated Organics in Groundwater, and Technical Protocol for Implementing Intrinsic Remediation with Long- Term Monitoring for Natural Attenuation of Fuel Contamination Dissolved in Groundwater available at http 11www afcee brooks of miller/toolbox htm) c) Can additional wells be placed in the plume, or can the injection rates from existing wells be redistributed in a way that would economically speed up remediation9 (Air sparging system optimization may be recommended as part of a separate study, if appropnate Such a study should only be recommended tf justif ed by potential cost savings) d) Evaluate the aboveground system for ability to achieve cost savings by reducing the number of wells Can changes be made in the above-ground system to achieve efficient operation at a reduced flow rate9 In some cases, the ca^acit� -� nP i r.,re*rio�nnR nrn_rtirnri„rt,vP wells may allow hi air flnw rates through the more YJ' 5.......-. J b..... r........- o contaminated parts of the site However blowers may need to be adjusted or possibly replaced by different sized units to accommodate changes in airflow 1 vacuum requirements e) If the ISAS system is accompanied by an SVE system, is it still necessary to capture the vapors with SVE? In some cases,there is no risk in allowing the sparged air to pass upward into the unsaturated zone without capture For aerobically degradable contaminant vapors,the sparged air may function in a manner similar to bioventing such 06/07/99 Page 5 of 6