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 SOIL WASHING

This profile provides the following general information about 
thermal desorption:

1.      Description
2.      Applicability
3.      Limitations
4.      Availability and vendor list
5.      Performance data and field applications
6.      Sources of information for this profile

1.      DESCRIPTION

Soil washing is a water-based process for scrubbing soils ex situ to 
remove contaminants.  The process removes contaminants from soils in 
one of two ways:

       By dissolving or suspending them in the wash solution (which 
     is later treated by conventional wastewater treatment methods). 

       By concentrating them into a smaller volume of soil through 
     particle size separation, gravity separation, and attrition 
     scrubbing (similar to those techniques used in sand and gravel 
     operations).  

Soil washing systems incorporating most of the removal techniques offer 
the greatest promise for application to soils contaminated with a wide 
variety of heavy metal, radionuclides, and organic contaminants.  
Commercialization of the process, however, is not yet extensive.

The concept of reducing soil contamination through the use of particle 
size separation is based on the finding that most organic and inorganic 
contaminants tend to bind, either chemically or physically, to clay, 
silt, and organic soil particles.  The silt and clay, in turn, are 
attached to sand and gravel particles by physical processes, primarily 
compaction and adhesion.  Washing processes that separate the fine 
(small) clay and silt particles from the coarser sand and gravel soil 
particles effectively separate and concentrate the contaminants into 
a smaller volume of soil that can be further treated or disposed of.  
Gravity separation is effective for removing high or low specific 
gravity particles such as heavy metal-containing compounds (lead, 
radium oxide, etc.).  Attrition scrubbing removes adherent contaminant 
films from coarser particles.  The clean, larger fraction can be 
returned to the site for continued use.



2.      APPLICABILITY

The target contaminant groups for soil washing are SVOCs, fuels, and 
inorganics.  The technology can be used on selected VOCs and pesticides.  
The technology offers the potential for recovery of metals and can 
clean a wide range of organic and inorganic contaminants from coarse-
grained soils.



3.      LIMITATIONS

Factors that may limit the applicability and effectiveness of the 
process include:

     Fine soil particles (e.g., silt, clays) may require the 
     addition of a polymer to remove them from the washing fluid.

     Complex waste mixtures (e.g., metals with organics) make 
     formulating washing fluid difficult.

     High humic content in soil may require pretreatment.

     The aqueous stream will require treatment



4.      AVAILABILITY AND VENDOR LIST

Soil washing is commercially available from a number of vendors.  
A full vendor list is provided below:

Alternative Remedial Technologies, Inc.         (813) 264-3506
B&W Nuclear Environmental Services, Inc.        (804) 948-4610
Benchem                                         (412) 361-1426
Bergmann USA                                    (615) 452-5500
Biogenesis        
Bio-Recovery Systems, Inc.                      (505) 523-0405
Biotrol, Inc.                                   (612) 942-8032
Canonie Environmental Services Corp.            (303) 790-1747
Divesco, Inc.                                   (601) 932-1934
Earth Decontaminators, Inc.                     (714) 262-2290
Geochem Division of Terra Vac                   (303) 988-8902
Lockheed Corporation                            (702) 897-3626
Nukem Development                               (713) 520-9494
OHM  Corporation                                (510) 256-6100
On-Site Technologies, Inc.                      (408) 371-4810
RREL                                       
Scientific Ecology Group, Inc.                  (412) 247-6255
Turboscope Velco Environmental Service          (713) 799-5289
Warren Spring Laboratory                        (44-438) 74-122 (UK)
West Pac Environmental, Inc.                    (206) 762-1190
Westinghouse Remediation Services, Inc.         (404) 299-4736



5.      PERFORMANCE DATA

At the present time, soil washing is used extensively in Europe but 
has had limited use in the United States.  During 1986-1989, the 
technology was one of the selected source control remedies at 
eight Superfund sites.

Soil washing is most commonly used in combination with the 
following technologies:  bioremediation, incineration, and 
solidification/stabilization.  Depending on the process used, 
the washing agent and soil fines are residuals that require further 
treatment.  When contaminated fines have been separated, coarse-
grain soil can usually be returned clean to the site.  The time to 
complete cleanup of the "standard" 18,200-metric-ton (20,000-ton) 
site using soil washing would be less than 3 months.



6.      Source:

Marks, Peter J., Walter J. Wujcik and Amy F. Loncar, October 1994. 
REMEDIATION TECHNOLOGIES SCREENING MATRIX AND REFERENCE GUIDE, 
SECOND EDITION.  DOD Environmental Technology Transfer Committee. 
NTIS No. PB95-104782.  Reproduced for the Bloomington, Indiana PCB 
Superfund Sites Bulletin Board with the permission of USAEC, 
SFIM-AEC-ETD, APG, MD.  Supplmented by MVA Consulting, Inc.

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