United States
                  Environmental Protection
                  Agency
Office of Solid Waste and
Emergency Response
(5102G)
&EPA       A Citizen's
                  In  Situ Flushing
               to
EPA 542-F-01-011
May 2001
www.epa.gov/superfund/sites
www.cluin.org
 The  Citizen's Guide Series
  EPA uses many methods to clean up pollution at Superfund and other sites. Some, like in situ flushing, are consid
  ered new or innovative. Such methods can be quicker and cheaper than more common methods. 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 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 in situ  flushing?

                    In situ flushing is a way to clean up harmful chemicals in polluted soil and groundwater by
                    pumping water or chemicals into the ground. This helps flush the harmful chemicals from the
                    ground by moving them toward wells that pump the chemicals out of the ground. The pro-
                    cess works in situ, which means the polluted soil is cleaned up in place and does not need to
                    be dug up.

                    How does it  work?

                    The goal of in situ flushing is to improve the effectiveness of pump and treat cleanup methods.
                    Pump and treat methods pump polluted groundwater up through wells to the ground surface
                    where it is cleaned up. (See^4 Citizen's Guide to Pump and Treat [EPA 542-F-01-025].)
                    When harmful chemicals don't dissolve in the groundwater, they can't easily be pumped out of
                    the ground. Some chemicals like solvents and heating oil exist as liquids but do not dissolve
                    easily in water. They are called non-aqueous phase liquids or NAPLs. NAPLs can remain in
                    the soil for many years and slowly dissolve into the groundwater. As a result, they can be a
                    source of groundwater pollution for a long time.

                    In situ flushing using chemicals like surfactants and cosolvents can help dissolve NAPLs.
                    Surfactants are commonly found in detergents and some food products. Cosolvents are
                    alcohols, like ethanol or methanol.  When used for in situ flushing, a surfactant or cosolvent is
                    mixed with water. The mixture is pumped down a well, or several wells, drilled in the polluted
                    area where it helps dissolve the NAPLs. The mixture also can help move the NAPLs toward
                    the wells.

                    At some sites, the surfactant mixture may stick or sorb to the soil. This may increase the
                    amount of surfactant required to remove the NAPL. If this happens, a cosolvent can be
                    added to the surfactants mixture to prevent the surfactant from sorbing to the soil.

                    In situ flushing works best in soil that is very permeable. In other words, groundwater can
                    flow through it easily. In situ flushing also works best if the soil underneath the polluted area is
                    not very permeable, like clay. The clay prevents the surfactant or cosolvent from moving
                    below the polluted area. When a clay layer does not exist, a surfactant foam method can
                    be used. In this method, air is pumped underground with the surfactant and water. The air
                    forms a foam that prevents the surfactant from moving beyond the polluted area.

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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.
1
                                       surfactant, cosolvent,
                                       or water mixture

                                                ground surface
                                    
                                                     -groundwater
                                                              level
                                                 polluted groundwater
                                                      polluted groundwater
                                                      removed and cleaned up
                                                      above ground
                         Is  in  situ  flushing  safe?

                         In situ flushing can be quite safe, but there are some potential hazards. Workers that handle the
                         chemicals pumped down the wells must wear protective clothing. Also, surfactant or cosolvent
                         left behind after cleanup may be harmful. But at some sites, scientists may want to leave small
                         amounts of surfactant or cosolvent in the polluted area to help with bioremediation. (See A
                         Citizen's Guide to Bioremediation [EPA 542-F-01-001].)
                             How long will it  take ?
                             The time it takes for in situ flushing to clean up a site depends on
                             several factors:
       size and depth of the polluted area
       type and amount of NAPL
       type of soil and conditions present
       how groundwater flows through the soil (How fast? Along what path?)
     Cleanup of a site can take months or years using in situ flushing.
Why  use  in  situ  flushing?

In situ flushing is used to help pump and treat groundwater. It is one of the few methods that can
help clean up NAPL in place. This avoids the expense of digging up the soil for disposal or
cleanup. Depending on the number of wells and the amount of surfactant or cosolvent needed, in
situ flushing can be expensive and difficult to use. However, in situ flushing has successfully
cleaned up many polluted sites and has been used, or is being used, at 16 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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