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
                                 ./•
                                 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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