Description:

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.

Synonyms:

DSERTS Code: M12 (Soil Flushing). 

Applicability:

Limitations:

• 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.

Data Needs:

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.

Performance Data:

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.

Detailed Cost Estimate

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.

• Laramie Tie Plant, WY

General FRTR Agency Contacts

Government Web Sites

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.

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