(In Situ Thermal Extraction Process)
The in situ thermal extraction process heats soil with steam injection, enhancing pump-and-treat and soil vapor extraction processes used to treat volatile organic compounds (VOC) and semivolatile organic compounds (SVOC). This process is an effective and relatively inexpensive technique to raise a target soil volume to a nearly uniform temperature.
As illustrated in the figure below, steam is introduced to the soil through injection wells screened in contaminated intervals. The steam flow sweeps contaminants to extraction wells. Groundwater and liquid contaminants are pumped from the extraction wells; steam, air, and vaporized contaminants are extracted under vacuum. After the soil is heated by steam injection, the injection wells can introduce additional agents to facilitate the cleanup.
Recovered vapors pass through a condenser. The resulting condensate is combined with pumped liquids for processing in separation equipment. Separated nonaqueous phase liquids (NAPL) can be recycled or disposed of, and the water is treated prior to discharge. The noncondensible gases are directed to a vapor treatment system consisting of (1) catalytic oxidation equipment, (2) activated carbon filters, or (3) other applicable vapor technologies. The in situ thermal extraction process uses conventional injection, extraction and monitoring wells, off-the-shelf piping, steam generators, condensers, heat exchangers, separation equipment, vacuum pumps, and vapor emission control equipment.
The in situ thermal extraction process removes VOCs and SVOCs from contaminated soils and groundwater. The process primarily treats chlorinated solvents such as trichloroethene (TCE), tetrachloroethene (PCE), and dichloro-benzene; hydrocarbons such as gasoline, diesel, and jet fuel; and mixtures of these compounds.
The process can be applied to rapid cleanup of source areas such as dense NAPL pools below the water table surface, light NAPL pools floating on the water table surface, and NAPL contamination remaining after conventional pumping techniques.
Subsurface conditions are amenable to biodegradation of residual contaminants, if necessary, after application of the thermal process. A cap is required for implementation of the process near the surface. For dense NAPL compounds in high concentrations, a barrier must be present or created to prevent downward percolation of the NAPLs. The process is applicable in less permeable soils with the use of novel delivery systems such as horizontal wells or fracturing.
This technology was accepted into the SITE Demonstration Program in August 1993. The demonstration is scheduled to occur at Hill Air Force Base (AFB) in Ogden, Utah. The Ogden Air Logistics Center Environmental Management Office and Armstrong Laboratory at Tyndall AFB, Florida are also participating in the demonstration.
From 1967 to 1979, unknown quantities of chlorinated solvents including TCE and PCE were disposed of in two unlined trenches at Hill AFB. These dense NAPL compounds migrated through the soil and shallow groundwater, pooling on top of a natural clay layer about 50 feet below the surface. The demonstration will be performed in this area, after most NAPLs have been recovered by conventional pumping.
EPA PROJECT MANAGER:
Paul dePercin
U.S. EPA
National Risk Management Research Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
513-569-7797
Fax: 513-569-7105
E-Mail:
dePercin.Paul@epamail.epa.gov
TECHNOLOGY DEVELOPER CONTACTS:
Lloyd Stewart
Praxis Environmental Technologies, Inc.
1440 Rollins Road
Burlingame, CA 94010
415-548-9288
Fax: 415-548-9287
Captain Jeff Stinson
U.S. Air Force
Armstrong Laboratory
Environmental Risk Management, AL/EQM-OL
139 Barnes Drive, Suite 2
Tyndall AFB, FL 32403-5319
904-283-6254
Fax: 904-283-6064