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4KCSti Idepression in the potentiometric surface Wells are spaced such that the cone of depression of each well overlaps those from adjacent wells The combined effect of the groundwater extraction system is to intercept and capture all impacted groundwater Constituents are drawn to the wells and recovered for treatment Treatment systems can consist of air strippers, activated carbon, ultra violet oxidation, or reverse osmosis The treated water must be re-mjected or permitted for disposal in a publicly-owned treatment works (POTW) system Groundwater extraction and treatment alone is generally not effective in attaining the State health based clean up levels In general, dissolved-phase concentrations at most sites treated solely by pump and treat technology tend to reach asymptotic levels above the health based clean up levels Continued use of this technology past this point would not be economically feasible IBiodegradation - Soil and Groundwater ' Biodegradation refers to an in-situ remedial process that uses natural attenuation to reduce or degrade organic constituents of concern (COCs) over tune The process uses natural degradation to reduce the concentrations of contaminants to below regulatory standards Biodegradation as a ' remedial option is usually coupled with institutional controls and long-term monitoring The principal COCs at the site are fuel-related constituents (e g , benzene, toluene, ethylbenzene, ' • xylenes, and MTBE) BTEX and MTBE are readily degradable in aerobic environments, and intrinsic bioremediation is frequently approved as part of remedial programs for fucl spill sites ' The dissolved-phase hydrocarbon concentrations within groundwater have exhibited a significant decrease in all wells, except MW-13, since groundwater monitoring and sampling was initiated in 1993 Natural attenuation appears to be occurring at the site, and would probably be part of the ' mass removal mechanism even if an active remediation system were installed To implement this approach would require a demonstration showing that the rate of degradation offsets the potential for off-site migration Also, the risk for potential exposure to contaminants must either be ' controlled or demonstrated to be within acceptable limits Sod samples collected from site borings were submitted for physicochemical and microbiological analyses The analyses revealed very low viable recoveries for heterotrophic and selective ' microorganisms at the dilutions tested The results suggested the possibility that some level of biotoxicity exists at the site Biodegradation of the groundwater may be an active process at this site However, soil analyses ' indicate that current subsurface soil conditions are not conducive to biodegradation The use of biodegradation alone would not be a viable option for this site ' Physical Containment Physical containment usually involves the construction of a slurry or cut-off wall across the flow 1