In-Situ Air Stripping (ISAS)

Description

In-Situ air stripping (ISAS) combines three technologies: air sparging, horizontal wells, and soil vapor extraction. ISAS uses horizontal wells to inject (sparge) air into the groundwater. The horizontal wells provide more effective access to horizontal groundwater plumes. As the air comes into contact with contaminants, they volatilize and rise through the soil. The volatile organic compounds (VOCs) are then extracted from overlying soils by standard soil vapor extraction. The air sparging process eliminates the need for surface groundwater treatment systems such as air strippers.

Limitations and Concerns

ISAS using horizontal wells may accelerate plume migration. If this occurs, it may be necessary to use ISAS in conjunction with a pump-and-treat system for hydraulic control.

Increasing the contaminant surface area exposed to oxygen enhances efficiency. Each application must be assessed and designed on a site-specific basis.

For ISAS to be effective, the contaminants of concern must be strippable (i.e., they volatilize when exposed to air). Most light hydrocarbons and chlorinated solvents meet this condition.

ISAS is effective at removing light nonaqueous phase liquids (LNAPLs) because they are mainly located at the top of the water table. It is not suitable for dense non-aqueous phase liquids (DNAPL).

Successful ISAS requires good contact between injected air, contaminated soils, and groundwater. ISAS is not well suited for sites with highly stratified soils with low permeability layers, fractured rock, or clay geology. ISAS does not effectively remediate large dilute plumes, but it is useful near source areas.

Applicability

ISAS has been demonstrated to remediate soils and groundwater contaminated with VOCs and fuels.

Technology Development Status

A full-scale demonstration was conducted by the U.S. Department of Energy at the Savannah River Integrated Demonstration. Long-term performance data from several years of operation are still required. Hence, this should be considered a technology that has only been field tested, although all of the equipment is commercially available.

Web Links

http://www.osti.gov/bridge/servlets/purl/7093-MSCtC9/webviewable/

Other Resources and Demonstrations

See descriptions of Air Sparging, Horizontal Wells and Soil Vapor Extraction

See http://www.osti.gov/bridge/servlets/purl/10160854-W3cNC5/native/ for description of demonstration at the Savannah River Plant.