Description:

The contaminants will either be degraded or retained in a concentrated form by the barrier material. The wall could provide permanent containment for relatively benign residues or provide a decreased volume of the more toxic contaminants for subsequent treatment.

Funnel and Gate

Modifications to the basic passive treatment walls may involve a funnel-and-gate system or an iron treatment wall. The funnel-and-gate system for in situ treatment of contaminated plumes consists of low hydraulic conductivity (e.g., 1E-6 cm/s) cutoff walls (the funnel) with a gate that contains in situ reaction zones. Ground water primarily flows through high conductivity gaps (the gates). The type of cutoff walls most likely to be used in the current practice are slurry walls or sheet piles. Innovative methods such as deep soil mixing and jet grouting are also being considered for funnel walls.

Iron Treatment Wall

An iron treatment wall consists of iron granules or other iron bearing minerals for the treatment of chlorinated contaminants such as TCE, DCE, and VC. As the iron is oxidized, a chlorine atom is removed from the compound by one or more reductive dechlorination mechanisms, using electrons supplied by the oxidation of iron . The iron granules are dissolved by the process, but the metal disappears so slowly that the remediation barriers can be expected to remain effective for many years, possibly even decades.

Barrier and post-closure monitoring tests are being conducted by the USAF, U.S. Navy, and DOE in field-scale demonstration plots and are being designed for actual contaminated sites. The range of materials available for augmenting existing barrier practice is broad. Two types of barriers have been the focus of initial efforts of this program, i.e., permeable reactive barriers and in-place bioreactors.

Passive treatment walls are generally intended for long-term operation to control migration of contaminants in ground water.

Synonyms:

Applicability:

Limitations:

• Passive treatment walls may lose their reactive capacity, requiring replacement of the reactive medium.
• Passive treatment wall permeability may decrease due to precipitation of metal salts.
• Depth and width of barrier.
• Limited to a subsurface lithology that has a continous aquitard at a depth that is within the vertical limits of trenching equipment.
• Volume cost of treatment medium.
• Biological activity or chemical precipitation may limit the permeability of the passive treatment wall.

Data Needs:

Data needs include hydraulic gradient; contaminant characteristics (depth, areal extent, type, and concentration); depth to ground water, including range of anticipated fluctuations; depth to impermeable barrier key-in; site stratigraphy; ground water hydrology; water quality, flow rate, and direction; soil permeability; and buffering capacity.

Performance Data:

Several full-scale and demonstration scale walls have been installed for remediation of ground water contaminated with chlorinated aliphatic hydrocarbons. These sites include Lowry AFB and Moffett Field NAS. Several more sites are currently being evaluated or have passive treatment walls scheduled for installation.

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

o       Width of the plume to be treated

·        Choice of supplemental amendments

·        Additional monitoring required by regulators

Cost Analysis

The following table represents estimated costs (by common unit of measure) to apply passive/reactive treatment wall 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:

Technical Documents from the Remediation Technologies Development Forum (RTDF) Web Site which includes Installation Profiles and Field Applications of Permeable Reactive Barrier Walls.

EPA, 1995. In Situ Remediation Technology Status Report: Treatment Walls, Office of Solid Waste and Emergency Response, EPA/540/K-94/004.

EPA, 1997. Permeable Reactive Subsurface Barriers for the Interception and remediation of Chlorinated Hydrocarbon and Chromium(VI) Plumes in Ground Water, EPA/600/F-97/008.

DOE, 1993. Technical Name: Barriers and Post-Closure Monitoring, Technology Information Profile (Rev. 2), DOE Protech Database, TTP No. AL-1211-25.

DOE, 1994. Technology Catalogue, First Edition. February.

Federal Remediation Technologies Roundtable, 1998. Remediation Case Studies: Innovative Groundwater Treatment Technologies, EPA/542/R-98/015.

• Pump and Treat and Permeable Reactive Barrier to Treat Contaminated Groundwater at the Former Intersil, Inc. Site, Sunnyvale, California
• Permeable Reactive Barrier to Treat Contaminated Groundwater at Moffett Federal Airfield, Mountain View, California
• In Situ Permeable Reactive Barrier for Treatment of Contaminated Groundwater at the U.S. Coast Guard Support Center, Elizabeth City, North Carolina

Hansen, W., et al., 1992. "Barriers and Post-Closure Monitoring", Briefing Chart, Los Alamos National Laboratory, Los Alamos, NM, TTP No. AL-1212-25.

USAF, 1997. Design Guidance for Application of Permeable Barriers to Remediate Dissolved Chlorinated Solvents, prepared by Battelle under contract to Environics Directorate, Armstrong Laboratory.

Vidic, R.D. and F.G. Pohland. "Technology Evaluation Report: Treatment Walls", GWRTAC Series TE-96-01.

• Tonolli Corporation, PA
• Lowry Air Force Base, CO
• Somersworth Sanitary Landfill Site, NH
• Moffett Field NAS, CA
• Brown's Battery Breaking Site, OU 2, PA
• Canadian Forces Base, Canada
• Borden Aquifer, Canada
• Air Force Demo Hill AFB, UT
• Los Alamos National Laboratory
• Former Intersil, Inc. Site, Sunnyvale, CA
• Moffett Federal Airfield, Mountain View, CA
• The U.S. Coast Guard Support Center, Elizabeth City, NC
• 

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A list of vendors offering In Situ Physical/Chemical Water 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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