United States
Environmental Protection
Agency
Office of Solid Waste and
Emergency Response
(5102G)
EPA 542-F-01-004
April 2001
www.epa.gov/superfund/sites
www.cluin.org
&EPA A Citizen's
to
Monitored Natural Attenuation
The Citizen's Guide Series
EPA uses many methods to clean up pollution at Superfund and other sites. 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 pro-
posed for use at your site. How do they work? Are they safe? This Citizen's Guide is one in a series to help
I answer your questions.
What is monitored natural attenuation?
Natural attenuation relies on natural processes to clean up or attenuate pollution in soil and
groundwater. Natural attenuation occurs at most polluted sites. However, the right conditions
must exist underground to clean sites properly. If not, cleanup will not be quick enough or
complete enough. Scientists monitor or test these conditions to make sure natural attenuation
is working. This is called monitored natural attenuation orMNA.
How does it work?
When the environment is polluted with chemicals, nature can work in four ways to clean it up:
1. Tiny bugs or microbes that live in soil and ground-
water use some chemicals for food. When they
completely digest the chemicals, they can change them
into water and harmless gases. (A Citizen's Guide to
Bioremediation [EPA 542-F-01-001] describes how
microbes work.)
chemical
chemical
2. Chemicals can stick or sorb to soil, which holds them in
place. This does not clean up the chemicals, but it can keep
them from polluting groundwater and leaving the site.
3. As pollution moves through soil and groundwater, it
can mix with clean water. This reduces or dilutes the
pollution.
groundwater
flow
chemical
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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.
4. Some chemicals, like oil and solvents, can evaporate, which
means they change from liquids to gases within the soil. If these
gases escape to the air at the ground surface, sunlight
may destroy them.
gases rise
through soil
ground surface
chemical
evaporates
MNA works best where the source of pollution has been removed. For instance, buried waste
must be dug up and disposed of properly. Or it can be removed using other available cleanup
methods. After the source is removed, the natural processes get rid of the small amount of
pollution that remains in the soil and groundwater. The soil and groundwater are monitored
regularly to make sure they are cleaned up.
Is it safe?
MNA can be a safe process if used properly. No one has to dig up the pollution, and nothing
has to be added to the land or water to clean it up. But MNA is not a "do nothing" way to clean
up sites. Regular monitoring is needed to make sure pollution doesn't leave the site. This
ensures that people and the environment are protected during cleanup.
How long will it f
The time it takes for MNA to clean up a site depends on
several factors:
• type and amounts of chemicals present
• size and depth of the polluted area
• type of soil and conditions present
These factors vary from site to site, but cleanup usually takes years to decades. MNA
is used when other methods will not work or are expected to take almost as long.
Sometimes MNA is used as a final cleanup step after another method cleans up most
of the pollution.
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Why use monitored natural attenuation?
Depending on the site, MNA may work just as well and almost as fast as other methods.
Because MNA takes place underground, digging and construction are not needed. As a result,
there is no waste to dispose of in landfills. This is less disruptive to the neighborhood and the
environment. Also, it allows cleanup workers to avoid contact with the pollution. MNA requires
less equipment and labor than most methods. Therefore, it can be cheaper. Monitoring for many
years can be costly, but it may cost less than other methods.
MNA is the only cleanup method being used at a few Superfund sites with groundwater pollu-
tion. At over 60 other sites with polluted groundwater, MNA is just one of the cleanup methods
being used. MNA also is used for oil and gasoline spills from tanks.
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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