Remediation Technologies Screening Matrix, Version 4.0 4.19 Soil Washing
(Ex Situ Soil Remediation Technology)
  Description Synonyms Applicability Limitations Site Information Points of Contact
Data Needs Performance Cost References Vendor Info. Health & Safety
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>>3.5 Ex Situ Physical/Chemical Treatment (assuming excavation)

      >>4.19 Soil Washing
Introduction>> Contaminants sorbed onto fine soil particles are separated from bulk soil in an aqueous-based system on the basis of particle size. The wash water may be augmented with a basic leaching agent, surfactant, pH adjustment, or chelating agent to help remove organics and heavy metals.

Description:

Figure 4-19: Typical Soil Washing Process Ex situ soil separation processes (often referred to as "soil washing"), mostly based on mineral processing techniques, are widely used in Northern Europe and America for the treatment of contaminated soil. Soil washing is a water-based process for scrubbing soils ex situ to remove contaminants. The process removes contaminants from soils in one of the followingtwo ways:
  • By dissolving or suspending them in the wash solution (which can be sustained by chemical manipulation of pH for a period of time); or
  • 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. However, attrition washing can increase the fines in soils processed. The clean, larger fraction can be returned to the site for continued use.

Complex mixture of contaminants in the soil (such as a mixture of metals, nonvolatile organics, and SVOCs) and heterogeneous contaminant compositions throughout the soil mixture make it difficult to formulate a single suitable washing solution that will consistently and reliably remove all of the different types of contaminants. for these cases, sequential washing, using different wash formulations and/or different soil to wash fluid ratios, may be required.

Soil washing is generally considered a media transfer technology. The contaminated water generated from soil washing are treated with the technology(s) suitable for the contaminants.

The duration of soil washing is typically short- to medium-term.

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Synonyms:

DSERTS Code: N15 (Soil Washing).

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Applicability:

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

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Limitations:

Factors that may limit the applicability and effectiveness of the process include:
  • 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 at demobilization.
  • Additional treatment steps may be required to address hazardous levels of washing solvent remaining in the treated residuals.
  • It may be difficult to remove organics adsorbed onto clay-size particles.

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Data Needs:

A detailed discussion of these data elements is provided in Subsection 2.2.1 (Data Requirements for Soil, Sediment, and Sludge). Particle size distribution (0.24 to 2 mm optimum range); soil type, physical form, handling properties, and moisture content; contaminant type and concentration; texture; organic content; cation exchange capacity; pH and buffering capacity. A complete bench scale treatability study should always be completed before applying this technology as a remedial solution.

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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 provides a cost effective and environmentally proactive alternative to stabilization and landfilling. Two pilot scale demonstrations were carried out at Fort Polk, Louisiana in 1996. These employed commercially available unit processes - physical separation/acid leaching systems. The system employed acetic acid as the leaching agent, and the other, hydrochloric acid. Input soil had a lead content of approximately 3500 mg/kg. The hydrochloric acid system was most effective. Processed soil had total lead concentration of 200 mg/kg and TCLP levels for lead of approximately 2 mg/L. The through put rate was approximately 6 tons per hour. Choice of acid leaching agent is a function of specific soil chemistry and degree of solubility required.

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Cost:

The key cost driver information and cost analysis was developed in 2006 using the Remedial Action Cost Engineering and Requirements (RACER) software.

Key Cost Drivers 

        Economy of Scale

o       Quantity of material treated has a large impact

        Processor speed

o       Also depends on the amount of waste being processed

Cost Analysis

The following table represents estimated costs (by common unit of measure) to apply soil washing technology at sites of varying size and complexity.   A more detailed cost estimate table which includes specific site characteristics and significant cost elements that contributed to the final costs can be viewed by clicking on the link below.

SOIL TECHNOLOGY:

Soil Washing

 

RACER PARAMETERS

Scenario A

Scenario B

Small Site

Large Site

 

 

 

COST PER CUBIC FOOT

$5

$2

COST PER CUBIC METER

$187

$70

COST PER CUBIC YARD

$142

$53

Detailed Cost Estimate

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References:

Treatment Technologies for Site Cleanup: Annual Status Report (ASR), Tenth Edition, EPA 542-R-01-004

Innovative Remediation Technologies:  Field Scale Demonstration Project in North America, 2nd Edition

Abstracts of Remediation Case Studies, Volume 4,  June, 2000, EPA 542-R-00-006

Guide to Documenting and Managing Cost and Performance Information for Remediation Projects - Revised Version, October, 1998, EPA 542-B-98-007

Nottingham Trent  University,1995. Interim Status Report, Enhancement Techniques for Ex Situ Separation Processes Particularly With Regard to  Fine Particles, Nottingham, United Kingdom, 

Battelle, 1997. Physical Separation and Acid Leaching: A Demonstration of Small-Arms Range Remediation at Fort Polk, Louisiana. Final report prepared for Naval Facilities Engineering Service Center (NFESC) and U.S. Army Environmental Center under contract with NFESC, Port Hueneme, CA.

Battelle, 1997. Physical Separation and Acid Leaching: A Demonstration of Small-Arms Range Remediation at Fort Polk, Louisiana. Implementation Guidance Handbook. Prepared for Naval Facilities Engineering Service Center (NFESC) and U.S. Army Environmental Center under contract with NFESC, Port Hueneme, CA.

BDM, 1997. Demonstration of Physical Separation/Leaching Methods for the Remediation of Heavy Metals-Contaminated Soils at Small-Arms Range Final Report. Prepared for U.S. Army Environmental Center (USAEC) and Naval Facilities Engineering Service Center under contract with USAEC, Aberdeen Proving Ground, MD.

BDM, 1997. Demonstration of Physical Separation/Leaching Methods for the Remediation of Heavy Metals-Contaminated Soils at Small-Arms Range Worldwide Search Report. Prepared for U.S. Army Environmental Center (USAEC) and Naval Facilities Engineering Service Center under contract with USAEC, Aberdeen Proving Ground, MD.

California Base Closure Environmental Committee (CBCEC), 1994. Treatment Technologies Applications Matrix for Base Closure Activities, Revision 1, Technology Matching Process Action Team, November, 1994.

EPA, 1989. Innovative Technology: Soil Washing, OSWER Directive 9200.5-250FS.

EPA, 1989. Soils Washing Technologies for: Comprehensive Environmental Response, Compensation, and Liability Act, Resource Conservation and Recovery Act, Leaking Underground Storage Tanks, Site Remediation.

EPA, 1990. Soil Washing Treatment, Engineering Bulletin, EPA, OERR, Washington, DC, EPA/540/2-90/017. Available from NTIS, Springfield, VA, Order No. PB91-228056.

EPA, 1991. Biotrol Soil Washing System, EPA RREL, series includes Technology Evaluation Vol. I, EPA/540/5-91/003a, PB92-115310; Technology Evaluation Vol. II, Part A, EPA/540/5-91/003b, PB92-115328; Technology Evaluation Vol. II, Part B, EPA/540/5-91/003c, PB92-115336; Applications Analysis, EPA/540/A5-91/003; Technology Demonstration Summary, EPA/540/S5-91/003; and Demonstration Bulletin, EPA/540/M5-91/003.

EPA, 1992. A Citizen's Guide to Soil Washing, EPA, OSWER, Washington, DC, EPA/542/F-92/003.

EPA, 1992. Bergmann USA Soil/Sediment Washing System, EPA RREL, Demonstration Bulletin, EPA/540/MR-92/075.

EPA, 1993. Bescorp Soil Washing System Battery Enterprises Site Brice Environmental Services, Inc., EPA RREL, Demonstration Bulletin, EPA/540/MR-93/503.

EPA, 1993. Biogenesis Soil Washing Technology, EPA RREL, series includes Demonstration Bulletin, EPA/540/MR-93/510; Innovative Technology Evaluation Report, EPA/540/R-93/510; and Site Technology Capsule, EPA/540/SR-93/510.

EPA, 1997. Best Management Practices (BMPs) for Soil Treatment Technologies: Suggested Operational Guidelines to Prevent Cross-media Transfer of Contaminants During Clean-UP Activities, EPA OSWER, EPA/530/R-97/007.

Federal Remediation Technologies Roundtable, 1995. Remediation Case Studies: Thermal Desorption, Soil Washing, and In Situ Vitrification, EPA/542/R-95/005.

Raghavan, R., D.H. Dietz, and E. Coles, 1988. Cleaning Excavated Soil Using Extraction Agents: A State-of-the-Art Review, EPA Report EPA 600/2-89/034.

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Site Information:

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Points of Contact:

General FRTR Agency Contacts

Technology Specific Web Sites:

Government Web Sites

Non Government Web Sites

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Vendor Information:

A list of vendors offering Ex Situ Physical/Chemical Soil Treatment is available from EPA REACH IT which combines information from three established EPA databases, the Vendor Information System for Innovative Treatment Technologies (VISITT), the Vendor Field Analytical and Characterization Technologies System (Vendor FACTS), and the Innovative Treatment Technologies (ITT), to give users access to comprehensive information about treatment and characterization technologies and their applications.

Government Disclaimer

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Health and Safety:

Hazard Analysis

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