United States
Environmental Protection
Agency
Solid Waste and
Emergency Response
(5102G)
EPA 542-F-96-006
April 1996
vvEPA
A Citizen's Guide to
In Situ Soil Flushing
Technology Innovation Office
Technology Fact Sheet
What is in situ soil flushing?
In situ soil flushing is an innovative treatment tech-
nology that floods contaminated soils with a solu-
tion that moves the contaminants to an area where
they are removed. "In situ"—meaning "in place"—
refers to treating the contaminated soil without dig-
ging up or removing it.
The specific contaminants in the soil at any particu-
lar site determine the type of flushing solution need-
ed in the treatment process. The flushing solution is
typically one of two types of fluids: 1) water only;
or 2) water plus additives such as acids (low pH),
bases (high pH) or surfactants (like detergents).
Water is used to treat contaminants that dissolve
easily in water. An acidic solution is a mixture of
water and an acid, such as nitric acid or hydrochloric
acid. Acidic solutions are used to remove metals
and organic contaminants, such as those typically
found in battery recycling or industrial chrome plat-
ing processes. For example, zinc contamination—
which can result from plating operations—would be
treated with an acidic solution. A basic solution is a
mixture of water and a base, such as sodium
hydroxide. (Ammonia is an example of a base com-
monly used in households.) Basic solutions are used
to treat phenols and some metals. A surfactant can
be a detergent or emulsifier. Emulsifiers help mix
substances that normally do not mix such as oil and
water. For this reason, surfactant solutions are effec-
tive at removing oily contaminants.
Researchers also are investigating the use of water
plus organic solvents as a flushing solution. Organic
solvents such as ethanol are used to dissolve certain
contaminants that water alone cannot dissolve.
How does it work?
Figure 1 on page 2 provides an illustration of one
type of in situ soil flushing process. The process be-
gins with the drilling of injection wells and extrac-
tion wells into the ground where the contamination
has been found. The number, location, and depth of
the injection and extraction wells depend on many
geological factors and engineering considerations.
Wells may be installed either vertically or horizon-
tally. In addition to placing the wells, other equip-
ment—such as a wastewater treatment system—
must be transported to or built on the site.
A Quick Look at In Situ Soil Flushing
Injects a washing solution into unexcavated soils to flush out contaminants.
Is most effective on soils with low silt or clay content.
Requires the drilling of injection and extraction wells on-site.
Is a transportable technology that can be brought to the site.
Requires greater understanding of the site's geology than some other technologies.
Printed on Recycled Paper
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The soil flushing equipment pumps the flushing
solution into the injection wells. The solution passes
through the soil, picking up contaminants along its
way as it moves toward the extraction wells. The
extraction wells collect the elutriate—the flushing
solution mixed with the contaminants.
The elutriate is pumped out of the ground through
the extraction wells. Here, the elutriate is typically
treated by a wastewater treatment system to remove
the contaminants. The contaminants are treated or
disposed of, and the treated water can either be
recycled for use in the flushing solution or disposed
of in another acceptable manner. It is because of
this circular process that in situ soil flushing systems
are often referred to as injection/recirculation
systems.
Any contaminated fumes or vapors that might be given
off during the wastewater treatment step of the process
are collected and treated.
How Is Soil Flushing Different From
Soil Washing?
With soil flushing, the soil is treated in place using
an injection/recirculation process. Soil washing
involves excavating the contaminated soil and
treating it at the surface in a soil washer.
with oily waste, surfactants can be added to the
flushing solution to remove them more easily from
the soil.
In addition, since soil flushing is conducted in situ, it
reduces the need for excavation, handling, or trans-
portation of the hazardous substances. The process
has been most effective in removing the contami-
nants such as those identified in Figure 2 on page 3.
Why consider in situ soil flushing?
In situ soil flushing can be tailored to treat specific
contaminants. For example, if a site is contaminated
Will it work at every site?
In situ soil flushing works best at sites with soil that
has spaces that permit the wash solution to move
Figure 1
The In Situ Soil Flushing Process (Using Vertical Wells)
Treated water (either recycled for use in washing
solution or discharged in another acceptable manner)
Washing solution
Treated
Emissions
Washing
Solution
ri
Separator
Concentrated
Residuals
Contaminant
Treatment
Washing
Solution
Injection
Well
(Further Treatment
or Disposal)
Washing solution/
Contaminant mixture
Extraction
Well
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What Is an Innovative Treatment
Technology?
Treatment technologies are processes
applied to hazardous waste or contaminated
materials to permanently alter their condition
through chemical, biological, or physical
means. Treatment technologies are able to
alter, by destroying or changing, contam-
inated materials so they are less hazardous
or are no longer hazardous. This may be
done by reducing the amount of contam-
inated material, by recovering or removing a
component that gives the material its haz-
ardous properties or by immobilizing the
waste.
Innovative treatment technologies are those
that have been tested, selected or used for
treatment of hazardous waste or
contaminated materials but lack well-
documented cost and performance data
under a variety of operating conditions.
through it. If the soil has a high percentage of silt or
clay, for example, the flushing solution can not easi-
ly move through the soil, so it can not easily make
contact with the contaminants. This limits the over-
all effectiveness of the soil flushing process. In ad-
dition, some flushing fluids contain additives which
may themselves create new groundwater contamina-
tion if they are not completely removed.
There are additional considerations for the use of
this technology. For example:
• The flow of the groundwater must be well
understood in order to design the well system for
a given site. Extensive field investigations may
be necessary to define the groundwater flow
completely.
• The makeup and arrangement of subsurface layers
must be well understood to be able to predict the
path of the flushing fluids and contaminants and
ensure that the contamination is not spread be-
yond the area from which it can be collected.
• Since in situ soil flushing is tailored to treat specif-
ic contaminants, it is not highly effective with
soils contaminated with a mixture of hazardous
substances, for example, metals and oils. It would
be difficult to prepare a flushing solution that
would effectively remove several different types
of contaminants at the same time.
Where is in situ soil flushing being
used?
Table 1 on page 4 lists some Superfund sites where
in situ soil flushing has been selected as a treatment
method.
Figure 2
Contaminants Considered
for Treatment by In Situ Soil Flushing
Contaminants
Industries
Where Used
Heavy metals (lead, Battery Recycling,
copper, zinc) Metal Plating
Halogenated solvents Drycleaning,
(TCE, trichloroethane) Electronics Assembly
Aromatics (benzene,
toluene, cresol,
phenol)
Wood Treating
Gasoline and fuel oils Petroleum, Automobile
PCBs and chlorinated Pesticide, Herbicide,
phenol Electric Power
Not all waste types and site conditions are comparable. Each
site must be individually investigated and tested. Engineering
and scientific judgment must be used to determine if a
technology is appropriate for a site.
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Table 1
Examples of Superfund Sites Using Soil Flushing
Name of Site
Lipari Landfill, NJ
Vineland Chemical, NJ
Ninth Avenue Dump, Ml
Lee Chemical, MO
Idaho Pole Company, MT
United Chrome Products, OR
Umatilla Army Depot, OR
Status**
Operational
In design
Completed
Operational
In design
Operational
Design complete
Type of Facility
Landfill
Pesticide manufacturing
Industrial landfill
Solvent recovery
Wood preserving
Chrome plating
Explosives storage
Contaminants
Volatile organic compounds
(VOCs), semi-volatile organic
compounds (SVOCs), metals
Metals
VOCs, polyaromatic
hydrocarbons (PAHs)
VOCs
SVOCs, PAHs
Metals
Explosives, propellents
For a listing of Superfund sites at which innovative treatment technologies have been used or selected for use,
contact NCEPI at the address in the box below for a copy of the document entitled Innovative Treatment
Technologies: Annual Status Report (7th Ed.), EPA 542-R-95-008. Additional information about the sites listed
in the Annual Status Report is available in database format. The database can be downloaded free of charge from
EPA's Cleanup Information bulletin board (CLU-IN). Call CLU-IN at 301-589-8366 (modem). CLU-IN's help line is
301-589-8368. The database also is available for purchase on diskettes. Contact NCEPI for details.
* Not all waste types and site conditions are comparable. Each site must be individually investigated and tested.
Engineering and scientific judgment must be used to determine if a technology is appropriate for a site.
"As of August 1995
For More Information
The publications listed below can be ordered free of charge by calling NCEPI at 513-489-8190 or faxing your request
to 513-489-8695. If NCEPI is out of stock of a document, you may be directed to other sources. You may write to
NCEPI at:
National Center for Environmental Publications and Information (NCEPI)
P.O. Box 42419
Cincinnati, OH 45242
Selected Alternative and Innovative Treatment Technologies for Corrective Action and Site Remediation: A
Bibliography of EPA Resources, January 1995, EPA 542-B-95-001. A bibliography of EPA publications about
innovative treatment technologies.
Physical/Chemical Treatment Technology Resource Guide, September 1994, EPA 542-B-94-008. A bibliography of
publications and other sources of information about soil flushing, soil washing, solvent extraction, and other
innovative treatment technologies.
Engineering Bulletin: In Situ Soil Flushing, May 1991, EPA 540-2-91-021.
Engineering Issue: Considerations in Deciding to Treat Contaminated Soils In Situ, EPA 540-S-94-500.
In Situ Remediation Technology Status Report: Surfactant Enhancement, EPA 542-K-94-003.
In Situ Remediation Technology Status Report: Cosolvents, EPA 542-K-94-006.
WASTECH® Monograph on So/7 Washing/Soil Flushing, ISBN #1-883767-03-2. Available for $49.95 from the American
Academy of Environmental Engineers, 130 Holiday Court, Annapolis, MD 21401. Telephone 410-266-3311.
NOTICE: This fact sheet is intended solely as general guidance and information. It is not intended, nor can it be relied upon, to create any rights enforceable by any
party in litigation with the United States. The Agency also reserves the right to change this guidance at any time without public notice.
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