Citizen's  Guide
          itu  Thermal"
What is In Situ Thermal Treatment?

In situ thermal treatment methods move or "mobilize"
harmful chemicals in soil and groundwater using heat.
The chemicals move through soil and groundwater
toward wells  where  they are collected and piped
to  the ground surface to be treated  using  other
cleanup methods. Some  chemicals are destroyed
underground  during  the heating process. Thermal
treatment  is described as  "in situ" because the heat
is applied underground directly to the contaminated
area. It can be particularly useful for chemicals called
"non-aqueous phase liquids" or "NAPLs," which do
not  dissolve readily  in groundwater and can  be a
source of  groundwater contamination for a long time
if not treated. Examples of NAPLs  include solvents,
petroleum, and creosote (a wood preservative).

How Does It Work?

In situ thermal treatment methods heat contaminated
soil, and  sometimes  nearby groundwater,  to very
high temperatures. The heat vaporizes (evaporates)
the chemicals and water changing them into gases.
These gases, also referred to as "vapors," can move
more easily through  soil.  The heating  process can
make it easier to remove NAPLs from both soil and
groundwater.  High temperatures also  can  destroy
some chemicals in the area being heated.

In situ thermal methods generate heat in different ways:

   Electrical resistance heating (ERH)  delivers
    an electrical  current between metal rods called
    "electrodes"  installed  underground.  The  heat
    generated as movement of the current meets
    resistance from  soil converts groundwater and
    water in soil into steam, vaporizing contaminants.

   Steam enhanced extraction (SEE) injects steam
    underground by pumping it through wells drilled in
    the contaminated area. The steam heats the area
    and mobilizes and evaporates contaminants.

   Thermal   conduction  heating  (TCH)  uses
    heaters placed in underground  steel pipes. TCH
    can heat the contaminated area hot enough to
    destroy some chemicals.
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The chemical and water vapors are pulled to collection
wells and brought to the ground surface by applying a
vacuum. (See A Citizen's Guide to Soil Vapor Extraction
and Air Sparging [EPA 542-12-018] for information on
how this is done.) The vapors are then treated above
ground using one of several cleanup methods available.
Or,  if concentrations are high,  the vapors  can be
condensed back to liquid chemicals and reused.

How Long Will It Take?

In situ thermal treatment might take a few months to a
few years to clean up a site. The actual cleanup time
will depend on several factors. For example, it might
take longer where:

   Contaminant concentrations are high.

   The contaminated area is large or deep.

   A variety of soil types are present, causing the
    ground to heat unevenly.

   The soil has a lot of organic matter, which causes
    chemicals to stick to the soil and not evaporate easily.

These factors vary from site to site.

Are In Situ Thermal Treatment Methods Safe?

In situ thermal treatment methods do not pose a threat to site workers or
the community when properly operated.  For instance, when using ERH, the
electrical current is prevented from traveling outside of the treatment area or to
aboveground structures by using common electrical grounding techniques. A
thermal treatment area is usually covered with an impermeable surface cover
(such as concrete, asphalt, or a heavy-duty tarp) to keep the heat and steam
underground.  Such seals also help prevent the release of chemical vapors
to the air.  In addition, workers test air samples to make sure that vapors are
being captured.

How Might It Affect Me?

In situ thermal treatment requires the use of drilling  equipment and other
heavy machinery to install wells or electrodes and to collect and treat vapors.
Neighborhoods near the site may experience some increased truck traffic as
the equipment is delivered and later removed. Nearby residents and businesses
also may hear operating equipment.

Why Use In Situ Thermal Treatment?

In situ  thermal  treatment  methods speed the  cleanup  of many types of
chemicals, and are among the few in situ methods that can clean up  NAPLs.
Thermal treatment can be used  in silty  or clayey soil where  other cleanup
methods do  not perform  well.  They  also can reach  contamination deep
underground or beneath buildings, which would otherwise be difficult or costly
to dig up to treat above ground.  In situ thermal treatment has  been selected
or is being used in cleanups of at least 12 Superfund sites as well as dozens of
other sites across the country.

                      Pipes to
             ERH system cleans up contaminated soil and groundwater.
                                       SEE was used to speed clean
                                       up of the Southern California
                                       Edison Co., Visalia Pole Yard
                                       Superfund site in California. Use
                                       of chemicals to treat wooden
                                       utility poles contaminated soil
                                       and groundwater at the facility.
                                       Conventional "pump and treat,"
                                       begun in 1984, did not show
                                       much progress in meeting
                                       cleanup objectives. In 1997,
                                       14 steam injection wells were
                                       installed around the contami-
                                       nated area. Steam was injected
                                       into the ground at depths of
                                       80-100 feet, vaporizing the
                                       chemicals and forcing them
                                       toward the collection wells.

                                       Initially, about 13,000 pounds
                                       of contaminants were pumped
                                       from the collection wells every
                                       day. SEE was stopped after
                                       three years when the wells
                                       began collecting less than 4
                                       pounds per day, indicating that
                                       most of the chemicals had been
                                       removed. The pump and treat
                                       system was turned off in 2004.
                                       Overall, about 1.3 million pounds
                                       of contaminants were removed,
                                       and groundwater contaminant
                                       concentrations were reduced to
                                       below drinking water standards.
                                       By using SEE as part of the
                                       cleanup effort, the overall site
                                       cleanup was reduced from an
                                       estimated 120 years to 20 years.

                                       For More Information
 For more information on this
 and other technologies in the
 Citizen's Guide Series, contact:
          U.S. EPA
    Technology Innovation &
     Field Services Division
 Technology Assessment Branch
          Or visit: In
NOTE: This fact sheet is intended solely as general 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.
United States
Environmental Protection
Office of Solid Waste and
Emergency Response
EPA 542-F-12-013
September 2012