United States Office of Solid Waste and EPA 542-F-01-012

Environmental Protection Emergency Response May 2001

Agency (5102G) www.epa.gov/superfund/sites

www.cluin.org

A Citizen’s Guide to In Situ

Thermal Treatment Methods

  EPA uses many methods to clean up pollution at Superfund and other sites. Some, like in situ thermal treatment

methods, are considered new or innovative. Such methods can be quicker and cheaper than more common

methods. If you live, work, or go to school near a Superfund site, you may want to learn more about cleanup

methods. Perhaps they are being used or are proposed for use at your site. How do they work? Are they safe?

This Citizen’s Guide is one in a series to help answer your questions.

  	 
 
 	 


In situ thermal treatment methods, in general, are ways to move or mobilize harmful chemicals

through soil and groundwater by heating them. The heated chemicals move through the soil and

groundwater toward underground wells where they are collected and piped to the ground surface.

There the chemicals can be treated above ground by one of the many cleanup methods available.

   

All thermal methods work by heating polluted soil and groundwater. The heat helps push

chemicals through the soil toward collection wells. The heat also can destroy or evaporate

certain types of chemicals. When they evaporate, the chemicals change into gases, which

move more easily through the soil. Collection wells capture the harmful chemicals and gases

and pipe them to the ground surface for cleanup. Thermal methods can be particularly useful

for chemicals called non-aqueous phase liquids or NAPLs, which do not dissolve or move

easily in groundwater. As a result, they can be a source of groundwater pollution for a long

time without proper treatment. In situ thermal methods include:

Steam injection: Forces or injects steam underground through wells drilled in the polluted

area. The steam heats the area and mobilizes, evaporates, and destroys the harmful chemicals.

Hot air injection: Similar to steam injection except hot air is injected through the wells

instead of steam. The hot air heats the soil causing the harmful chemicals to evaporate.

Hot water injection: Also similar to steam injection except that hot water is injected through

the wells instead of steam. The hot water mobilizes chemicals like NAPLs.

Electrical resistance heating: Delivers an electric current underground through wells made

of steel. The heat from the current converts groundwater and the water in the soil to steam,

which evaporates the harmful chemicals.

Radio frequency heating: Typically involves placing an antenna that emits radio waves in

a well. The radio waves heat the soil causing the harmful chemicals to evaporate.

Thermal conduction: Supplies heat to the soil through steel wells or with a blanket that

covers the ground surface. As the polluted area heats up, the harmful chemicals are destroyed or evaporated. The blanket is used where the polluted soil is shallow. Steel wells are

used when the polluted soil is deep.
2



	


write the Technology

Innovation Office at:

U.S. EPA (5102G)

1200 Pennsylvania Ave.,

NW

Washington, DC 20460

or call them at

(703) 603-9910.

Further information also

can be obtained at

www.cluin.org or

www.epa/gov/

superfund/sites.

 	 
 
 	 
 


In situ thermal treatment methods are safe when properly operated. When there is a chance that

gases may pollute the air, a cover is placed over the ground to prevent their escape. And EPA

tests the air to make sure that the dust and gases are being captured. Scientists are also studying

whether heat can kill microbes or help microbes bioremediate chemicals. (See A Citizen’s

Guide to Bioremediation [EPA 542-F-01-001].)

 
 	 
 
 	 


Thermal methods speed the cleanup of many types of chemicals in the ground. Faster cleanups

can mean lower cleanup costs. Depending on the number of wells needed, thermal methods can

be expensive. However, they are some of the few methods that can help clean up NAPL in

place. This avoids the expense of digging up the soil for disposal or cleanup. Thermal methods

can work in some soils (such as clays) where other cleanup methods do not perform well. They

also offer a way of reaching pollution deep in the ground where it would be difficult or costly to

dig. Thermal methods are being used at several dozen sites across the country, including a few

Superfund sites.

NOTE: This fact sheet is intended solely as general guidance and information to the public. It is not intended, nor can it be relied

upon, to create any rights enforceable by any party in litigation with the United States, or to endorse the use of products or services

provided by specific vendors. The Agency also reserves the right to change this fact sheet at any time without public notice. well

collection

well

well

steam

steam

steam

steam

gases and polluted water 

removed and cleaned up

ground surface

groundwater level

polluted

soil and

groundwater

steam steam

Steam Injection

Cleaning soil and groundwater with thermal methods may take only

a few months or several years. The time it takes depends on three

major factors that vary from site to site:

• type and amounts of chemicals present

• size and depth of the polluted area

• type of soil and conditions present