In-Situ Enhanced Soil Mixing
In-Situ Enhanced Soil Mixing (ISESM) is a treatment technology for remediating soils contaminated with volatile organic compounds (VOCs). ISESM combines a number of in-situ soil treatment technologies that can treat fine-grained soils. In processes where chemicals, air and/or steam are added, soil mixing allows good access to all soil particles and the spaces between particles. The technology is particularly suited to shallow applications (i.e., down to about 45 feet) above the water table. Four variations of ISESM technology have been evaluated. They are briefly described below.
Limitations and Concerns
VOC emissions must be treated.
Hydrogen peroxide is an oxidizing agent. Proper handling precautions must be taken to prevent spills and to protect workers because bulk quantities are used.
ISESM requires surface access at all locations where soils are contaminated. This rules out its effective use if contamination underlies buildings or parking lots.
If ISESM is used to enhance biological activity (e.g., injection of nutrients), high contaminant levels and metals may be toxic to microorganisms.
In-situ soil mixing for stabilization is commonly used at sites with soil contaminated with organics. It is also appropriate for soils contaminated with metals. ISESM with the injection of hot air, ambient air, or hydrogen peroxide has been demonstrated to remediate effectively clay-rich soils contaminated with VOCs in the unsaturated zone. If used for stabilization, it can immobilize metals.
Technology Development Status
In-situ soil mixing has been used for a number of years in the construction industry. Soil mixing with stabilization was demonstrated under the EPA SITE Program in 1990 for polychlorinated biphenyl (PCB)-contaminated soils. Improvements in equipment, such as more mobile and scaled-down mixing equipment, as well as additional experience, will improve performance.
Other Resources and Demonstrations
See http://www.osti.gov/bridge/servlets/purl/7415-lPwPap/webviewable/7415.PDF for a description of a U.S. Energy Department demonstration at Portsmouth.
See http://www.osti.gov/bridge/servlets/purl/12389-MD2mYl/webviewable/ for description of thermal in-situ soil mixing at Argonne National Lab.