Remediation Technologies Screening Matrix, Version 4.0 4.7 Soil Flushing
(In 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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>>3.2 In Situ Physical/Chemical Treatment

      >>4.7 Soil Flushing
Introduction>> Water, or water containing an additive to enhance contaminant solubility, is applied to the soil or injected into the ground water to raise the water table into the contaminated soil zone. Contaminants are leached into the ground water, which is then extracted and treated.

Description:

Figure 4-7:
Typical Soil Flushing System
In situ soil flushing is the extraction of contaminants from the soil with water or other suitable aqueous solutions. Soil flushing is accomplished by passing the extraction fluid through in-place soils using an injection or infiltration process. Extraction fluids must be recovered from the underlying aquifer and, when possible, they are recycled.

Cosolvent Enhancement

Cosolvent flushing involves injecting a solvent mixture (e.g., water plus a miscible organic solvent such as alcohol) into either vadose zone, saturated zone, or both to extract organic contaminants. Cosolvent flushing can be applied to soils to dissolve either the source of contamination or the contaminant plume emanating from it. The cosolvent mixture is normally injected upgradient of the contaminated area, and the solvent with dissolved contaminants is extracted downgradient and treated above ground.

Recovered ground water and flushing fluids with the desorbed contaminants may need treatment to meet appropriate discharge standards prior to recycle or release to local, publicly owned wastewater treatment works or receiving streams. To the maximum extent practical, recovered fluids should be reused in the flushing process. The separation of surfactants from recovered flushing fluid, for reuse in the process, is a major factor in the cost of soil flushing. Treatment of the recovered fluids results in process sludges and residual solids, such as spent carbon and spent ion exchange resin, which must be appropriately treated before disposal. Air emissions of volatile contaminants from recovered flushing fluids should be collected and treated, as appropriate, to meet applicable regulatory standards. Residual flushing additives in the soil may be a concern and should be evaluated on a site-specific basis.

The duration of soil flushing process is generally short- to medium-term.

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Synonyms:

Cosolvents Enhancement; Surfactant Flooding.

DSERTS Code: M12 (Soil Flushing). 

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Applicability:

The target contaminant group for soil flushing is inorganics including radioactive contaminants. The technology can be used to treat VOCs, SVOCs, fuels, and pesticides, but it may be less cost-effective than alternative technologies for these contaminant groups. The addition of environmentally compatible surfactants may be used to increase the effective solubility of some organic compounds; however, the flushing solution may alter the physical/chemical properties of the soil system. The technology offers the potential for recovery of metals and can mobilize 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:
  • Low permeability or heterogeneous soils are difficult to treat.
  • Surfactants can adhere to soil and reduce effective soil porosity.
  • Reactions of flushing fluids with soil can reduce contaminant mobility.
  • The potential of washing the contaminant beyond the capture zone and the introduction of surfactants to the subsurface concern regulators. The technology should be used only where flushed contaminants and soil flushing fluid can be contained and recaptured.
  • Aboveground separation and treatment costs for recovered fluids can drive the economics of the process.

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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). Treatability tests are required to determine the feasibility of the specific soil-flushing process being considered. Physical and chemical soil characterization parameters that should be established include soil permeability, soil structure, soil texture, soil porosity, moisture content, total organic carbon (TOC), cation exchange capacity (CEC), pH, and buffering capacity.

Contaminant characteristics that should be established include concentration, solubility, partition coefficient, solubility products, reduction potential, and complex stability constants. Soil and contaminant characteristics will determine the flushing fluids required, flushing fluid compatibility, and changes in flushing fluids with changes in contaminants.

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Performance Data:

Soil flushing is a developing technology that has had limited use in the United States. Typically, laboratory and field treatability studies must be performed under site-specific conditions before soil flushing is selected as the remedy of choice. To date, the technology has been selected as part of the source control remedy at 12 Superfund sites. This technology is currently operational at only one Superfund site; a second was scheduled to begin operation in 1991. EPA completed construction of a mobile soil-flushing system, the In Situ Contaminant/Treatment Unit, in 1988. This mobile soil-flushing system is designed for use at spills and uncontrolled hazardous waste sites. There has been very little commercial success with this technology.

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Cost:

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

Key Cost Drivers 

        Soil Permeability

o       The primary cost driver is soil permeability.  Soils with lower permeability are more recalcitrant to soil flushing thus remediation time can be significantly increased which increases costs. 

        Depth to Groundwater

o       Depth to groundwater is the secondary cost driver, with a deeper water table causing a higher cost to complete.

Cost Analysis

The following table represents estimated costs (by common unit of measure) to apply soil flushing 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 Flushing

 

RACER PARAMETERS

Scenario A

Scenario B

Scenario C

Scenario D

Small Site

Large Site

Easy

Difficult

Easy

Difficult

 

 

 

 

 

CUBIC YARDS PROCESSED

1,388

1,388

5,550

5,550

COST PER CUBIC YARD

$32

$49

$18

$27

COST PER 1000 CUBIC YARDS

$32,320

$48,729

$18,420

$26,853

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


AATDF, 1997. Technology Practices Manual for Surfactants and Cosolvents, Technical Report, Document No. TR-97-2.

EPA, 1991. In Situ Soil Flushing, Engineering Bulletin, EPA/540/2-91/021.

EPA, 1994. In Situ Remediation Technology Status Report: Cosolvent, Engineering Bulletin, EPA/542/K-94/006.

EPA, 1996. A Citizen's Guide to In Situ Soil Flushing, Technology Fact Sheet, EPA/542/F-96/006.

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.

Nash J., R.P. Traver, and D.C. Downey, 1986. "Surfactant-Enhanced In Situ Soils Washing", USAF Engineering and Services Laboratory, Florida. ESL-TR-97-18, Available from NTIS, Springfield, VA, Order No. ADA188066.

Sturges, S.G., Jr., P. McBeth, Jr., R.C. Pratt, 1992. "Performance of Soil Flushing and Groundwater Extraction at the United Chrome Superfund Site," Journal of Hazardous Materials, El Savior Science Pub., B.V., Amsterdam, Vol. 29, pp. 59-78.

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Site Information:

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Points of Contact:

General FRTR Agency Contacts

Technology Specific Web Sites:

Government Web Sites

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Vendor Information:

A list of vendors offering In 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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