United States
Environmental Protection
Agency
Solid Waste and
Emergency Response
(5102G)
EPA 542-F-96-002
April 1996
vvEPA
A Citizen's Guide to
Soil Washing
Technology Innovation Office
Technology Fact Sheet
What is soil washing?
Soil washing is a technology that uses liquids (usu-
ally water, sometimes combined with chemical addi-
tives) and a mechanical process to scrub soils. This
scrubbing removes hazardous contaminants and con-
centrates them into a smaller volume. Hazardous
contaminants tend to bind, chemically or physically,
to silt and clay. Silt and clay, in turn, bind to sand
and gravel particles. The soil washing process sepa-
rates the contaminated fine soil (silt and clay) from
the coarse soil (sand and gravel). When completed,
the smaller volume of soil, which contains the major-
ity of the fine silt and clay particles, can be further
treated by other methods (such as incineration or
bioremediation) or disposed of according to state and
federal regulations. The clean, larger volume of soil
is not toxic and can be used as backfill.
How does soil washing work?
A simplified drawing of the soil washing process is
illustrated in Figure 1 on page 2. The equipment is
transportable so that the process can be conducted at
the site. The first step of the process is to dig up the
contaminated soil and move it to a staging area
where it is prepared for treatment. The soil is then
sifted to remove debris and large objects, such as
rocks. The remaining material enters a soil scrub-
bing unit, in which the soil is mixed with a wash-
ing solution and agitated. The washing solution
may be simply water or may contain additives,
like detergent, which remove the contaminants
from the soil. This process is very similar to
washing laundry. The washwater is drained out of
the soil scrubbing unit and the soil is rinsed with
clean water. The larger scale soil washing equip-
ment presently in use can process over 100 cubic
yards of soil per day.
The heavier sand and gravel particles in the pro-
cessed soil settle out and are tested for contami-
nants. If clean, this material can be used on the
site or taken elsewhere for backfill. If traces of
contaminants are still present, the material may be
run through the soil washer again or collected for
alternate treatment or off-site disposal. Off-site
disposal may be regulated by the Resource Con-
servation Recovery Act (RCRA) or the Toxic
Substance Control Act (TSCA).
A Quick Look at Soil Washing
Separates fine-grained particles (silt and clay) from coarse-grained particles (sand and gravel).
Significantly reduces the volume of contaminated soil.
Is a relatively low-cost alternative for separating waste and minimizing volume required for subsequent
treatment.
Is a transportable technology that can be brought to the site.
Printed on Recycled Paper
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The contaminated silt and clay in the washwater
settle out and are then separated from the
washwater. The washwater, which now also
contains contaminants, is treated by wastewater
treatment processes so it can be recycled for
further use. As mentioned earlier, the washwater
may contain additives, some of which may inter-
fere with the wastewater treatment process. If this
is the case, the additives must be removed or
Not All Soil Is Created Equal
Soil is comprised of fine-grained (silt and clay) and
coarse-grained (sand and gravel) particles, organic
material (decayed plant and animal matter), water,
and air. Contaminants tend to readily bind,
chemically or physically, to silt, clay, and organic
material. Silt, clay, and organic material, in turn, bind
physically to sand and gravel. When the soil contains
a large amount of clay and organic material, the
contaminants attach more easily to the soil and,
therefore, are more difficult to remove than when a
small amount of clay and organic material is present.
neutralized by "pretreatment" methods before the
washwater goes to wastewater treatment.
Once separated from the washwater, the silt and
clay are tested for contaminants. If all the con-
taminants were transferred to the washwater and
the silt and clay are clean, they can be used at the
site or taken elsewhere for use as backfill. If still
contaminated, the material may be run through
the soil washing process again, or collected for
alternate treatment or off-site disposal in a permit-
ted RCRA or TSCA landfill.
Why consider soil washing?
Soil washing can be used as a technology by
itself, but is often used in combination with other
treatment technologies. Perhaps the principal use
of soil washing is as a volume reduction tech-
nique in which the contaminants are concentrated
in a relatively small mass of material. The larger
the percentage of coarse sand and gravel in the
material to be processed (which can be cleaned
and perhaps returned to the site), the more cost-
effective the soil washing application will be.
Figure 1
The Soil Washing Process
Recycled Water
I
f\ Washing^
I Solution
// ^\
On-site If no
Wastewater -^ 1
Treatment /\.
/ Does \
^,^±1 -• I ». Soil / washwater \!f to off-site
:^^S=- — _....% ^ Scrubbing fc- Washwater *-< contain ^-^V wastewater
Contaminated Soil Unit
I |
Oversized Debris : '!
treatment or Clean sand and
disposal) gravel
(return to site)
x mterrermg / treatment
\ariri itivps?/
Contaminated
material (to other
treatment or
disposal)
Clean silt and clay
(return to site)
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Ideally, the soil washing process would lead to a
volume reduction of about 90% (which means
only 10% of the original volume would require
further treatment). Wastes with a high percentage
of fine silt and clay will require a larger quantity
of material to go on to subsequent, more expensive
treatment. These soils may not be good candidates
for soil washing.
Soil washing is used to treat a wide range of
contaminants, such as metals, gasoline, fuel oils,
and pesticides. There are several advantages to
using this technology. Soil washing:
• Provides a closed system that remains unaf-
fected by external conditions. This system
permits control of the conditions (such as the
pH level and temperature) under which the soil
particles are treated.
• Allows hazardous wastes to be excavated and
treated on-site.
• Has the potential to remove a wide variety of
chemical contaminants from soils.
• Is cost-effective because it can be employed as
a pre-processing step, significantly reducing the
quantity of material that would require further
treatment by another technology. It also creates
a more uniform material for subsequent treat-
ment technologies.
Will soil washing work at every site?
Soil washing works best when the soil does not
contain a large amount of silt or clay. In some
cases, soil washing is best applied in combination
with other treatment technologies, rather than as a
technology by itself.
Removal of contaminants can often be improved
during the soil washing process by adding chemi-
cal additives to the washwater. However, the
presence of these additives may cause some
difficulty in the treatment of the used wastewater
and the disposal of residuals from the washing
process. Costs of handling and managing the
additives have to be weighed against the amount
of improvements in the performance of the soil
washing process.
Where has soil washing been used?
At the King of Prussia site in New Jersey, soil
washing was used to remove metal contamination
such as chromium, copper, mercury, and lead
from 19,000 tons of soil and sludge at a former
industrial waste reprocessing facility. The soil
washing process was able to clean the materials to
meet clean-up goals for eleven metals. For ex-
ample, chromium levels went from 8,000 milli-
grams chromium per kilogram of soil (mg/kg) to
480 mg/kg. Table 1 on page 4 lists some of the
Superfund sites where soil washing has been
selected.
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, contaminated materials so that they are less hazardous or
are no longer hazardous. This may be done by reducing the amount of contaminated material, by
recovering or removing a component that gives the material its hazardous 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 still lack well-documented cost and
performance data under a variety of operating conditions.
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Table 1
Examples of Superfund Sites Where Soil Washing Has Been Selected *
Name of Site Status** Medium Contaminants
Myers Property, NJ In design Soil, sediment Metals
Vineland Chemical, NJ In design Soil Metals
GE Wiring Devices, PR In design Soil, sludge Metals
Cabot Carbon/Koppers, FL In design Soil Semi-volatile organic compounds
(SVOCs), polyaromatic hydrocarbons
(PAHs), metals
Whitehouse Waste Oil Pits Predesign Soil, sludge Volatile organic compounds (VOCs),
PCBs, PAHs, metals
Cape Fear Wood Preserving Design complete Soil PAHs, metals
Moss American, Wl Predesign Soil PAHs
Arkwood, AR In design Soil, sludge SVOCs, dioxins, PAHs
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
Publications with "EPA" document numbers can be ordered free of charge by either calling 513-489-8190, faxing your
request to 513-489-8695, or writing to NCEPI at the address below. If NCEPI is out of stock of a document, you may
be directed to other sources.
National Center for Environmental Publications and Information (NCEPI)
P.O. Box 42419
Cincinnati, OH 45242
Publications with "PB" document numbers are available from the National Technical Information Service (NTIS) at
1-800-553-6847. There is a charge for these documents. Mail orders can be sent to:
National Technical Information Service (NTIS)
5285 Port Royal Road
Springfield, VA 22161
Selected Alternative and Innovative Treatment Technologies for Corrective Action and Site Remediation: A
Bibliography of EPA Information Resources, EPA 542-B-95-001. A bibliography of EPA publications about
innovative treatment technologies.
Physical/Chemical Treatment Technology Resource Guide, EPA 542-B-94-008. A bibliography of publications and
other sources of information about soil washing and other innovative treatment technologies.
Engineering Bulletin: Soil Washing Treatment, PB91-228056/XAB.
Abstracts of Remediation Case Studies, EPA 542-R-95-001.
WASTECH® Monograph on Soil 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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