A Citizen’s Guide to

Solidification/Stabilization

? ? EPA uses many methods to clean up pollution at Superfund sites. If you live, work, or go to school near a Superfund 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 slow the

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 chemicals.

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

water

tank

cleanup

materials

polluted soil ground level

mixing of

cleanup

materials and

polluted soil clean soil

United States Office of Solid Waste and EPA 542-F-01-024

Environmental Protection Emergency Response December 2001

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

www.cluin.org

The Citizen’s Guide Series
2

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

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.

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.

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.

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.

How long will it take?