United States
Environmental Protection
Agency
Office of Solid Waste and
Emergency Response
(5102G)
EPA542-F-01-024
December 2001
www.epa.gov/superfund/sites
www.cluin.org
&EPA A Citizen's Guide to
Solidification/Stabilization
The Citizen's Guide Series
EPA uses many methods to clean up pollution at Superfund sites. If you live, work, or go to school near a Super-
fund site, you may want to learn more about these 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.
What Is solidification/stabilization?
Solidification/stabilization refers to a group of cleanup methods that prevent or slowthe
release of harmful chemicals from polluted soil or sludge. These methods usually do not
destroy the chemicals—they just keep them from moving into the surrounding environment.
Solidification refers to a process that binds the polluted soil or sludge and cements it into a
solid block. Stabilization refers to changing the chemicals so they become less harmful or less
mobile. These two methods are often used together to prevent exposure to harmful chemi-
cals.
How do they work?
Solidification involves mixing polluted soil with a substance, like cement, that causes the soil
to harden. The mixture dries to form a solid block that can be left in place or removed to
another location. The solidification process prevents chemicals from spreading into the
surrounding environment Rain or other water cannot pickup or dissolve the chemicals as it
\
cleanup
materials
ground level
mixing of
cleanup
materials and
polluted soil
clean soil
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For more
information
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.
moves through the ground. Solidification does not get rid of the harmful chemicals, it simply
traps them in place.
Stabilization changes harmful chemicals into substances that are less harmful or less mobile. For
example, soil polluted with metals can be mixed with lime. The lime reacts with metals to form
metal hydroxides. The metal hydroxides do not move through and out of the soil as easily.
Solidification/stabilization methods may or may not require the soil to be removed. Sometimes it
is better to dig up the soil and place it in large mixers above ground to be sure that all of the
polluted soil mixes with the cleanup materials, such as cement and lime. The mixture may then
be returned to the ground at the site or placed in a landfill. At other sites, instead of digging up
the soil, it is mixed in place with the cleanup materials. Then it is covered with clean soil or
pavement. After solidification/stabilization is completed, EPA tests the surrounding soil to make
sure no pollution was missed.
Is solidification/stabilization safe?
In order to make sure of the safety of the remedy, EPA tests the final mixture to confirm proper
sealing of the harmful chemicals and for strength and durability of the solidified or stabilized
materials. Sometimes EPA will place use restrictions on areas that have received solidification or
stabilization. These land use restrictions can prevent future damage to the treated area.
How long will it take?
Solidification/stabilization may take weeks or months to complete,
depending on several factors that vary from site to site:
• types and amounts of chemicals present
• size and depth of the polluted area
• types of soil and geologic conditions
• whether the mixing occurs in place or in mixing tanks
Why use solidification/stabilization?
Solidification/stabilization provides a relatively quick and low cost way to protect from the threat
posed by harmful chemicals, especially metals. Solidification/stabilization has been chosen as
part of the remedy at 183 Superfund sites across the country.
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.
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