United States Office of Solid Waste and EPA 542-F-01-011

Environmental Protection Emergency Response May 2001

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

www.cluin.org

A Citizen’s Guide to

In Situ Flushing

? ? EPA uses many methods to clean up pollution at Superfund and other sites. Some, like in situ flushing, are considered 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 process 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 A 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.
2

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.

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.

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].)

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. well well

polluted groundwater

groundwater

level

surfactant, cosolvent, 

or water mixture

polluted groundwater 

removed and cleaned up

above ground

ground surface

NAPL