A Citizen's Guide tc
In Situ Chemical Oxi
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What Is In Situ Chemical Oxidation?
Chemical oxidation uses chemicals called "oxidants"
to help change harmful contaminants into less toxic
ones. It is commonly described as "in situ" because it
is conducted in place, without having to excavate soil
or pump out groundwater for aboveground cleanup.
In situ chemical oxidation, or "ISCO," can be used to
treat many types of contaminants like fuels, solvents,
and pesticides. ISCO is usually used to treat soil and
groundwater contamination in the source area where
contaminants were originally released. The source area
may contain contaminants that have not yet dissolved
into groundwater. Following ISCO, other cleanup
methods, such as pump and treat or monitored natural
attenuation, are often used to clean up the smaller
amounts of contaminants left behind. (See A Citizen's
Guide to Pump and Treat [EPA 542-F-12-017] and A
Citizen's Guide to Monitored Natural Attenuation [EPA
542-F-12-014].)
How Does It Work?
When oxidants are added to contaminated soil and
groundwater, a chemical reaction occurs that destroys
contaminants and produces harmless byproducts.
To treat soil and groundwater in situ, the oxidants
are typically injected underground by pumping them
into wells. The wells are installed at different depths
Pump
OxidantTank
JantTank ^^ Piping
^t^^^^^^_
Undissolved J^
Contaminant
Dissolved
Contaminant
(pink)
-Injection Well
Groundwater
Table
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Monitoring
Wells v.
in the source area to reach as much dissolved and
undissolved contamination as possible. Once the
oxidant is pumped down the wells, it spreads into the
surrounding soil and groundwater where it mixes and
reacts with contaminants.
To improve mixing, the groundwater and oxidants
may be recirculated between wells. This involves
pumping oxidants down one well and then pumping
the groundwater mixed with oxidants out another
well. After the mixture is pumped out, more oxidant is
added, and it is pumped back (recirculated) down the
first well. Recirculation helps treat a larger area faster.
Another option is to inject and mix oxidants using
mechanical augers or excavation equipment. This may
be particularly helpful for clay soil.
The four major oxidants used for ISCO are
permanganate, persulfate, hydrogen peroxide and
ozone. The first three oxidants are typically injected
as liquids. Although ozone is a strong oxidant, it is a
gas, which can be more difficult to use. As a result, it
is used less often.
Catalysts are sometimes used with certain oxidants. A
catalyst is a substance that increases the speed of a
chemical reaction. For instance, if hydrogen peroxide
is added with an iron catalyst, the mixture becomes
more reactive and destroys more contaminants than
hydrogen peroxide alone.
Following treatment, if contaminant concentrations
begin to climb back up or "rebound," a second or
third injection may be needed. Concentrations will
rebound if the injected oxidants did not reach all of the
contamination, or if the oxidant is used up before all the
contamination is treated. It may take several weeks to
months for the contamination to reach monitoring wells
and to determine if rebound is occurring.
ISCO may produce enough heat underground to cause
the contaminants in soil and groundwater to evaporate
and rise to the ground surface. Controlling the amount
of oxidant helps avoid excessive heat, and if significant
gases are produced, they can be captured and treated.
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How Long Will It Take?
ISCO works relatively quickly to clean up a source area. Cleanup may take a few months
or years, rather than several years or decades. The actual cleanup time depends on
several factors that vary site to site. For example, ISCO will take longer where:
• The source area is large.
• Contaminants are trapped in hard-to-reach areas like fractures or clay.
• The soil or rock does not allow the oxidant to spread quickly and evenly.
• Groundwater flow is slow.
• The oxidant does not last long underground.
Is ISCO Safe?
The use of ISCO poses little risk to the surrounding community. Workers wear
protective clothing when handling oxidants, and when handled properly, these
chemicals are not harmful to the environment or people. Because contaminated
soil and groundwater are cleaned up underground, ISCO does not expose
workers or others at the site to contamination. Workers test soil and groundwater
regularly to make sure ISCO is working.
How Might It Affect Me?
Nearby residents and businesses may see drilling rigs and tanker trucks with
oxidants and supplies as they are driven to the site. Residents may also hear the
operation of drilling rigs, pumps, and other equipment leading up to and during
the injection period. Following an injection, however, the cleanup process occurs
underground with little aboveground disruption. Workers may visit the site to
collect soil and groundwater samples to monitor cleanup progress.
Why Use ISCO?
ISCO is usually selected to
clean up a source area, where it
destroys the bulk of contaminants
in situ without having to dig up
soil or pump out groundwater for
aboveground treatment. This can
save time and money. ISCO has
successfully cleaned up many
contaminated sites and has been
selected or is being used at around
40 Superfund sites and many
other sites across the country.
/SCO system installed behind a small drycleaning facility.
Example
Groundwater near a former
wastewater treatment plant at
the Naval Air Station Pensacola
in Florida was contaminated
with solvents and acids from
painting and electroplating.
A groundwater pump and
treat system had operated for
more than 10 years to control
migration of contaminated
groundwater. However, it did
not do much to lower the
concentrations of contaminants.
ISCO using hydrogen peroxide
with an iron catalyst was
chosen to reduce contaminant
concentrations in the source
area enough to allow monitored
natural attenuation to complete
the cleanup.
The natural chemistry of the
site's groundwater was found
to limit the effectiveness of the
first phase of injections. In the
second phase, a chemical was
added to the reagent mix to
stabilize the oxidant mixture.
Contaminant levels fell
substantially. The successful
use of ISCO at this site was
estimated to save several
million dollars compared with
continued pump and treat.
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
(703) 603-9910
Or visit:
www.cluin.org/chemox
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
Agency
Office of Solid Waste and
Emergency Response
(5102G)
EPA 542-F-12-011
September 2012
www.epa.gov/superfund/sites
www.cluin.org
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