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L • MW-25S, MW-28, MW-29, and MW-30 indicate that the TPHg and benzene plumes may have reached cleanup objectives 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 environment? There are still elevated concentrations of dissolved petroleum hydrocarbons in groundwater that dictate that the system should continue to operate 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 remediation? ENSR has proposed that additional ISAS wells be installed in the vicinity of MW-3 and MW-11 which would more directly treat the existing plumes of TPHg and benzene in groundwater beneath the site 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 rate? In some cases, the capacity gained by removing non-productive wells may allow higher air flow rates through the more contaminated parts of the site However, blowers may need to be adjusted or possibly replaced by different sized units to accommodate changes in airflow/vacuum requirements It is unlikely that the compressor will need to be replaced because it is sufficiently sized to acheive the system objectives As stated previously in this document, ENSR will perform future site visits to better evaluate individual ISAS well performance Moreover, ENSR will determine if any sparge wells should be removed from the current sparging program because they are not in an area of concentrated contaminants 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 that biological processes in the unsaturated zone consume much of the contaminant vapor Yes, it is still necessary to capture the vapors with SVE The SVE system has been effective in extracting volatilized petroieum hydrocarbons in unit B As stated previously in this document, the site exhibited contaminant rebound and plume migration while the SVE system was smut down ENSR will continue to operate the SVE system until it no longer a feasible remediation option s u__ �.- f 66- w�t.�..iii barn t_naidarArih Yes when operated I rias pulsing v. %19, 7S independently the ISAS system is operated in pulse operations mode one week on 1 one week off Due to the manifolded piping design and layout, the ISAS wells can not be sequentially operated using a programmable timer g Other technologies ENSR is considering upgrades to the ISAS system that includes dedicated piping runs for each ISAS well • 9 Supplemental Notes and Data ENSRs Process Flow Diagram