Air Sparging - Technology Overview

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Air sparging involves injecting a gas (usually air/oxygen) under pressure into the saturated zone to volatilize groundwater contaminants and to promote biodegradation in saturated and unsaturated soils by increasing subsurface oxygen concentrations. Vola tilized vapors migrate into the vadose zone where they are extracted via vacuum, generally by a soil vapor extraction system. The term biosparging is sometimes used interchangeably with air sparging to highlight the bioremediation aspect of the treatment process or can refer to situations where biodegradation is the dominant remedial process, with volatilization playing a secondary role.

Air sparging has been used to address a broad range of volatile and semivolatile groundwater and soil contaminants including gasoline and other fuels and associated BTEX components and chlorinated solvents. According to information reviewed, sites with r elatively permeable, homogeneous soil conditions favor the use of air sparging due to greater effective contact between sparged air and the media being treated and effective migration/extraction of volatilized vapors. Other appropriate site conditions me ntioned include relatively large saturated thicknesses and depths to groundwater. These factors both control the area of influence of a sparging well, and if saturated thickness/depth to groundwater are small, the number of wells required for adequate co verage may become cost-prohibitive.

Several applications of air sparging technology are discussed which report that, when applied properly, this technique can be a cost effective method for meeting remedial objectives within reasonable time frames. Air sparging reportedly can be more effec tive than pump-and-treat methods since 'contaminants desorb more readily into the gas phase than into groundwater' and since increased volatilization can overcome the diffusion-limited extraction of VOCs from groundwater. Another reported advantage of ai r sparging is that in contrast to vapor extraction, it can be used to treat contamination in the capillary fringe and below the water table. Bioventing, also a modification of vapor extraction technology, is briefly contrasted with air sparging. With bioventing, extraction or injection of air into the vadose zone increases subsurface oxygen concentration, promoting bioremediation of unsaturat ed soil contaminants. This technique is applicable to all biodegradable contaminants, but has been applied most frequently and reportedly most successfully to sites with petroleum hydrocarbon contamination.

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