United States Office of Solid Waste and EPA 542-F-01-008

Environmental Protection Emergency Response May 2001

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

www.cluin.org

A Citizen’s Guide to

Soil Washing

  EPA uses many methods to clean up pollution at Superfund and other sites. Some, like soil washing, 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 know 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.

  	 



Soil washing “scrubs” soil to remove and separate the portion of the soil that is most

polluted. This reduces the amount of soil needing further cleanup. Soil washing alone may

not be enough to clean polluted soil. Therefore, most often it is used with other methods that

finish the cleanup.


   



Chemicals tend to stick or sorb to some types of soil more than others. For instance, chemicals sorb more to fine-grained soils like silt and clay than to larger-grained soils like sand and

gravel. The silt and clay, in turn, tend to stick to sand and gravel. Soil washing helps separate

the silt and clay from the larger-grained, cleaner soils. It works best when the soil contains a

much bigger portion of the larger-grained soils than the fine-grained ones. Soil washing can

clean up a variety of chemicals, such as fuels, metals, and pesticides, that can sorb to soil.

Before using soil washing, soil dug from the polluted area is sifted to remove large objects,

like rocks and debris. The sifted soil is placed in a machine called a scrubbing unit. Water,

water reused

clean water

clean soil

polluted soil

to second cleanup

method or landfill

wash

water

scrubbing

unit

treatment

plant

water and

detergent

scrubbing unit

polluted

soil (sifted)
2

The time it takes to clean up a site using soil washing depends on

several factors:

• amount of silt, clay, and debris in the soil

• type and amount of pollution in the soil

• size of scrubbing unit (The largest units can clean up to 100 cubic yards of

soil per day.)

Cleanup usually takes weeks to months, depending on the site.



	


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.

and sometimes detergents, are added to the polluted soil in the scrubbing unit. The mixture of

soil and water is passed through sieves, mixing blades, and water sprays. This washes the silt

and clay from the larger-grained soil and separates them. Some of the pollution may dissolve in

the water or float to the top. The polluted wash water is removed and cleaned up at a treatment

plant. The clean water then can be reused in the scrubbing unit or discharged.

The silt and clay, which contain most of the pollution, are tested for chemicals. Sometimes all of

the pollution is removed in the wash water, but most often the silt and clay need further cleanup.

The silt and clay may be washed again in the scrubbing unit or cleaned using another method

like bioremediation or thermal desorption. (See A Citizen’s Guide to Bioremediation [EPA

542-F-01-001] or A Citizen’s Guide to Thermal Desorption [EPA 542-F-01-003].) Another option is to dispose of the polluted soils in a landfill.

The sand and gravel that settle to the bottom of the scrubbing unit also are tested for chemicals.

If the sand and gravel are clean, they can be placed back on the site. If pollution is still present,

they are washed again in the scrubbing unit. If necessary, another method is used to finish the

cleanup.

 	 
 


Soil washing is usually performed at the site. This avoids the risks involved with trucking polluted soil from the site to a cleanup facility. During digging and cleanup, air pollution control

equipment takes care of dust and other potential air pollution problems. Chemicals are seldom

released from the scrubbing unit to the air. However, EPA tests the air at the site to ensure that

chemicals are not released in harmful amounts. EPA also tests the soil to be sure it is clean

before it is placed back on the site. When properly designed and operated, soil

washing is quite safe.

  	 



The greatest advantage of soil washing is that it reduces the amount of soil needing further

cleanup. This reduction lowers the cost of cleanup and the cost for disposing of polluted

material.

Soil washing can remove many types of pollution. It also works when the soil is very polluted,

but may not be cost-effective for small amounts of pollution. It is also not as cost-effective on

soils with a large amount of silt or clay. Soil washing is being used at six Superfund sites and

other 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.