This process enhances the naturally occurring biological activities in the contaminated subsurface soil. Circulating either a nutrient and oxygen-enriched water-based solution or a forced air movement which provides oxygen in the soil enhances the naturally occuring microbes (U.S. EPA 1991a). In the latter process, also called bioventing, the air flow rate is lower than in vapor extraction since the objective is to deliver oxygen while minimizing volatilization and the release of contaminants to the atmosphere. The technology is effective for nonhalogenated volatiles and fuel hydrocarbons. In addition, the contaminant toxicity is reduced or even eliminated. The technology, however, is less effective for nonbiodegradable compounds and for soils with low permeability.
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