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.