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Bioventing Technology Wer ­ige Page 2 of 5 <br /> XI <br /> Cometabolic bioventing is applicable to contaminants such as trichloroethylene (TCE), <br /> trichloroethane (TCA), ethylene dibromide, and dichloroethylene (DC,E) that resist direct <br /> aerobic degradation. <br /> w <br /> MAIAN <br /> The following factors may limit the applicability and effectiveness of the process: <br /> . Very high contaminant concentrations may be toxic to microorganisms. <br /> . Subsurface heterogeneity can interfere with efficienf!aeration of the contaminated <br /> zone. <br /> . Low-permeability soils are difficult to treat. <br /> . The presence of the water table within several feet Of the surface can reduce <br /> bioventing performance. <br /> . Vapors can build up in basements within the radius of influence of air injection wells, a <br /> problem that can be alleviated by extracting air near1he structure of concern. <br /> . Low soil moisture content may limit biodegradation and the effectiveness of bioventing, <br /> which tends to dry out the soils. <br /> . Off-gas monitoring at the soil surface may be required when soils are aerated through <br /> air injection. <br /> . Aerobic biodegradation of many chlorinated compounds may not be effective unless <br /> either a co-metabolite is present or,an anaerobic cycle is used. <br /> . Low ambient temperatures can significantly decrease biodegradation rates. <br /> . Heavy metals are not treated by this method and can be toxic to microorganisms. <br /> Bioventing is a medium-to long-term technology. Cleanup ranges from 6 months to 5 years. <br /> The duration of operation and maintenance is dependent on the following conditions: <br /> . Cleanup goals <br /> . The volume of in situ media requiring treatment <br /> . Contaminant concentrations and distributions <br /> . Achievable biodegradation rates j <br /> . In situ characteristics including permeability and anisotropy(&i h'.b +''Jn.9 <br /> $10 to $50 per cubic yard <br /> The major cost items included in the cost estimate range for bioventing and cometabolic <br /> http://enviro.nfesc.navy.mil/erb/restoration/technologies/remed/bio/bio-06.asp 6/17/2004 <br /> j <br />