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.

  1. Soil mixing combined with vapor extraction and air injection. The mixing auger is moved up and down to assist in the removal of contaminant vapors. At the same time, ambient air is injected to volatilize contaminants. The vapors are collected in a shroud covering the treatment area, and they are run through a treatment unit.
  2. Soil mixing combined with vapor extraction and hot air injection. This process is the same as ambient air injection except that hot air or steam is injected to increase the amount of contaminants that are volatilized.
  3. Soil mixing with hydrogen peroxide injection. Contaminated soil is mixed with ambient air that contains a mist of diluted hydrogen peroxide (H2O2) solution. The H2O2 solution chemically oxidizes the VOCs to carbon dioxide (CO2), free chlorine, and water.
  4. Soil mixing with grout injection for solidification/stabilization. Contaminated soil is mixed as a cement grout and injected under pressure to solidify and immobilize the contaminated soil in a concrete-like form.

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.

Web Links

Other Resources and Demonstrations

See descriptions of Physical and Chemical Solidification/Stabilization and Chemical Extraction.

See for a description of a U.S. Energy Department demonstration at Portsmouth.

See for description of thermal in-situ soil mixing at Argonne National Lab.