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C L E A k G R O U P Environmental SCrvIces appropriate for reducing concentrations of aromatic and Iighter hydrocarbons associated with ' gasoline, in unstratified sediments of moderate to high permeability Further, the infected oxygen partitions to a dissolved-phase and can enhance the aerobic biodegradation of contaminants ' Generally, this option is always operated with S VE to capture and treat vapors escaping from the groundwater ' The results of the pilot study performed at the site indicate that AS as essential if SVE technology is to be successful at this site During pilot testing air flow rates improved more than 100% with ' AS, from 8 5 cfm at a applied vacuum of 40 an w c to 22 4 cfm at the same applied vacuum The only drawback to AS as a groundwater remediation option is that it does not exert hydraulic ' control over the dissolved-phase plume Recent groundwater momtonng results indicate that the plume indeed appears to be stable and mostly limited to the area of the site Further, fuel has not ' been dispensed at the site since at least 1992 when the UST system was removed Therefore, plume control does not factor heavily in selection of a clean-up technology for this site Additionally, although experience suggests that AS is effective at removing light to mid range gasoline hydrocarbons (i e BTEX) from the dissolved-phase, it may have difficulty achieving non-detectable dissolved-phase TPHg concentrations This option would also require the ' installation of several AS wells (Figure 7) ' 6 3 2 Groundwater Extraction and Treatment Groundwater extraction and treatment has been proven as an effective means of controlling ' contaminant migration and reducing contaminant levels Although dissolved concentrations can be reduced through groundwater extraction, this method generally will not bring dissolved ' contaminant concentrations to below the stringent clean-up levels identified However, once asymptotic concentrations are reached, further reduction an concentrations generally slow down considerably, and natural attenuation becomes the primary process of contaminant reduction ' The chemical properties of gasoline range hydrocarbons suggest that groundwater extraction for contaminant mass removal alone is ineffectual It as a more useful technology an situations with ' MTBE contamination, because it is more soluble than gasoline hydrocarbons but has a higher Henry's Constant, making an-situ volatilization difficult However, MTBE is not a contaminant ' of concern at this site The greatest benefit of groundwater extraction comes from exerting hydraulic control over a migrating plume and lowering the water table to expose soil to the ' effects of vapor extraction ' ZB 3 78C CAP 15 November 24,2002