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Working to Restore Nature groundwater Hydrocarbon vapors entrained in the air bubbles rise through the saturated zone into the vadose zone Control of off-gas in the vadose zone is accomplished using a conventional vapor extraction system I The advantage of air-sparging systems is that air sparging can reduce dissolved-phase hydrocarbons in groundwater more effectively than "pump-and-treat" systems alone This increased hydrocarbon removal results from air-sparging reducing dissolved-phase i hydrocarbons by direct volatilization within the water-bearing zone By contrast, pump and treat systems require dissolved hydrocarbons to be hydraulically drawn toward the well for removal The hydraulically-induced migration of groundwater toward the recovery well is I often slow (depending on geology and hydrogeology), and is compounded by the retardation of dissolved hydrocarbons as they flow through soil An additional advantage of air sparging is that it can often remove adsorbed-phase hydrocarbons in the saturated soil zone more effectively than groundwater pumping alone Finally, since air sparging systems do not generally create a hydraulic capture zone,potential offsite contaminants from a second source may be less likely to be drawn toward the site I 6.0 PROPOSED REMEDIAL ACTION PLAN Based on the results of previous subsurface investigations, RESNA proposes the following 1 primary activities which comprise the remedial action plan 6;1 System Designs and Preparation of Plans I This phase of the proposed work will include engineering calculations, preparation of a list of equipment and selection of materials and instrumentation, preparation of Plans and Specifications including site and remediation compound layout, remediation compound equipment pad and fence details, trench and section details, and a process and 30003-13 11