Contaminant migration to areas surrounding a pollution source is a major environmental concern and methods are needed to control the spreading of pollution. The Containment Subprogram seeks to develop in situ technologies for pollution containment and is supporting investigations of new barrier materials, contaminant absorbers or neutralizers, and emplacement methods for barrier formation that do not require soil excavation. These technologies could provide short-term containment while the source plume is being remediated or long-term containment for sites presenting no immediate danger or requiring development of new remediation methods.
Barriers can be designed to be impermeable to water flow (hydraulic barriers), or can be semi-permeable, allowing water to pass but retaining the pollutant. Both types are being studied in this subprogram.
Impermeable barriers made with clays or cement/clay mixtures are widely used in construction. These barriers are effective in slowing water flow, but their use at contaminated sites can be limited by the need to excavate (and dispose of) contaminated soil from the placement trench. Clay may also be chemically attacked by leachates from the waste material, leading to degradation of the plugging effect of the clay and diffusion of contamination. Proper moisture content must be maintained to prevent shrinkage cracks in the clay. These deficiencies may be overcome through development of new barrier concepts, materials, and construction techniques. New synthetic binders and polymers are being evaluated for long-term stability and effectiveness as sealants. Inorganic grouts are also being studied for use with or without clays.
Developing semi-permeable barriers that control contaminant mobility without affecting groundwater flow is a major goal of the Containment Subprogram. By placing a substance in the barrier zone that absorbs or reacts with the target contaminant(s), pollutants can be physically trapped or chemically converted to a harmless form. Capacity and long-term effectiveness of such barriers are principal concerns of this research.
Forming barriers in situ by injection from the surface can decrease construction and waste disposal costs and can be useful for replenishing barriers that have lost their effectiveness over time. Development of barrier emplacement methods that do not involve soil excavation would be an important advancement of this technology. Frozen barriers in both non-arid and arid soils are being evaluated as part of this R&D effort.
This investigation is examining a number of substances that can immobilize chemical and radionuclide contaminants in groundwater beneath waste sites. Substances and processes under investigation include adsorption of chlorinated hydrocarbons from groundwater using a variety of organic materials, reductants to destroy chlorinated hydrocarbons and induce precipitation of various metals and oxyanions, and zeolites to sequester mobile metals.
Significant changes in mobility can be achieved through changes in oxidation state. Immobilization can also occur through surface adsorption of active substances, such as iron oxide or clays, or with ion exchange materials.
In addition to examining barrier technologies that involve construction to place the barrier, this program will also be investigating various methods to inject reagents into the subsurface. These techniques would minimize the excavation and management of potentially contaminated soils (see Figure 1.1).
Technology Needs
In situ remediation of contaminants at disposal sites would be significantly enhanced if techniques existed that could target mobile substances without restricting groundwater movement. Control of groundwater requires limiting surface water penetration and vadose zone movement. Errors in control can lead to release of contaminated water. Complete control may require caps, liners, lateral barriers, and possibly, the installation of a pumping system.
Barriers with partial permeability allow selective immobilization of the hazardous components. Selective barriers are needed for a range of substances including organic solvents, anions, and cations. For contaminant mixtures, a combination of different barrier sorbents may be necessary. This investigation will provide data on a variety of selective sorbent materials and examine methods of barrier placement that avoid excavation.
Accomplishments
This investigation will be carried out in collaboration with Ebasco Services,
Inc. (Richland, Washington), and the Westinghouse Hanford Company. Laboratory
investigations using an unsaturated flow apparatus (UFA)
will be performed at Washington State University. A co-investigator
will synthesize some test compounds at Eastern Montana College.
Details on the efficacy of various chemical reagents in sequestering
contaminants and the use of the UFA
will be published in
DOE technical reports and outside journal articles. Details on barrier
emplacement and non-destructive monitoring will be shared in appropriate
engineering literature.
Because chemical barrier reagents have applications in other containment activities such as caps and liners, data and results will be available to designers and engineers of these waste management systems.
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This investigation is examining liquids which, when injected into the subsurface, produce nearly-inert impermeable barriers through a very large increase in viscosity. Appropriate emplacement of these substances provides an effective containment of the contaminated zone by trapping and immobilizing both the contaminant and the plume. (See Figure 1.2).
This project will identify and characterize promising materials and evaluate
their containment potential by means of laboratory pilot-scale experiments and
field testing and demonstration. The general purpose
TOUGH2 model,
developed at the Lawrence Berkeley Laboratory (LBL) is being modified to
simulate barrier fluid behavior and to design experiments.
The first type of barrier fluid under examination belongs to the polybutene family. Polybutenes are chemically and biologically inert, hydrophobic and impermeable to water and gases, and are approved by the Federal Drug Administration for food contact. Their performance is unaffected by the soil and waste type, and is only controlled by their drastic viscosity dependence on temperature. The second type, colloidal silica, is a silicon-based chemical grout that poses no health hazard, is unaffected by filtration, and is chemically and biologically inert. Its containment performance is controlled by the gelation time, which depends on pH, temperature, the chemistry of the injected suspension, and chemistry and mineralogy of the aquifer porous medium. The third type of barrier fluid is polySiloXane. These fluids are chemically and biologically inert silicon-based polymers used for medical implants. They are mixtures of two fluids, are unaffected by the aquifer or waste chemistry, and their containment performance depends on temperature and the ratio of the two constituents.
Technology Needs
The strong adsorption of many contaminants to soil particles makes physical extraction slow or ineffective. Excavation of contaminated soils and disposal in protected facilities is very expensive. Containment on-site and control of groundwater transport can limit the off-site threat, and may supply a long-term solution.
A barrier containment system that does not require excavation would be a useful groundwater contamination control technique. Formation of a barrier with surface injected components that polymerize or change their viscosity under aquifer temperature and pressure conditions would allow barrier emplacement without excavation. In situations where complete control is necessary, an impermeable barrier is preferred over the sorption barrier.
In some areas aquifer mineralogy or regulatory restrictions may preclude the use of one or another barrier component. A variety of barrier systems must be available to match the range of contaminants and circumstances.
Accomplishments
Texas A&M University in College Station is evaluating the performance of barrier fluids in large two-dimensional laboratory experiments using their specialized facilities. UC Berkeley is involved in the selection and rheological study of polymer-type barrier fluids.
The new technologies and the corresponding design package will be made available for use throughout the DOE Environmental Restoration program, as well as other U.S. agencies (EPA and DOD). Contamination problems expected to be especially amenable to barrier containment include localized (``point-like'') sources. Many DOE sites would be candidates for the pilot-and field-scale application of the technologies, including the Hanford Underground Storage Tanks Integrated Program, Mixed Waste Integrated Program, the Buried Waste Integrated Demonstration Program, as well as the Rocky Flats site, the Nevada Test Site, the Savannah River site (for localized sources), and the Lawrence Livermore National Laboratory (where much pertinent information may be available from the ``clean site'' steam injection pilot). Many industrial sites with ``point-like'' contamination problems are also candidates for the application of these technologies.
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This project is examining the potential application of a bentonite/mineral wax formulation, developed in Germany, and an inorganic grout, developed in France, as barrier materials for DOE sites (see Figure 1.3). Because these materials have been used for grouting, bringing them to regulatory and public acceptability within the U.S. should be rapid.
This investigation is examining the compatibility of these barrier formulations within the range of DOE soils and waste types. Technical challenges include lateral permeation of the soils, physical and hydraulic stability of the barrier over time, and the regulatory acceptance of the overall approach and grout materials.
Technology Needs
A groundwater control system that is injectable from the surface and forms within the aquifer removes the need to excavate trenches and construct barriers. A material that is resistant to deterioration from aquifer and contaminant chemistry would meet significant waste site remediation needs throughout the complex. Materials that do not contain synthetic compounds or have been used elsewhere may gain regulatory acceptance faster than those using unusual or manufactured substances.
This investigation is examining some currently available injectable grouts that have shown promise in Europe. Their application to the arid site conditions and resistance to waste components are the focus of this study.
Accomplishments
This project is a cooperative effort of Golder Associates and the European licensees MIBRAG (Germany) and Societe Hoechst Francaise (France). The materials were identified through the International Technology Exchange Program (ITEP). Results will be made available through this and other international efforts.
The Underground Storage Tank Integrated Demonstration sites at Hanford, Oak Ridge, Savannah River, Fernald, and INEL will all potentially benefit from these relatively advanced technologies. The Sandia Mixed Waste Landfill is the probable site for demonstration of effectiveness. Other potential users include a number of DOD sites with leaking underground storage tanks as well as industrial facilities such as refineries and fuel terminals.
With DOE's assistance this technology should mature rapidly. The German company is searching for an American affiliate to manage applications in North America. The French group has a U.S. division to manufacture and distribute its formulation. Speedy transfer to the private sector is expected.
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This research is examining the sorption and immobilization capacity of a natural iron mineral for a number of site contaminants, and its use in the formation in situ of a permeable barrier that removes target contaminants but does not impede groundwater flow.
Ferric oxyhydroxide or hydrated iron oxide is a naturally occurring non-hazardous substance that has sorption affinities for a number of inorganic contaminants found at DOE sites. Such contaminants as uranium, molybdenum, copper, lead, zinc and radium can potentially be removed from groundwater.
The iron is injected as a solution in water. Reaction underground with aquifer mineral alkalinity converts it to the sorbing phase. Precipitation within the aquifer pores coats the rock particles forming a barrier zone around the contaminated area. This coating extracts the contaminants moving with the groundwater and confines them in the barrier zone (see Figure 1.4).
The objectives of this investigation are:
Construction of an impermeable barrier system can be expensive in terms of excavation, hazardous waste disposal, and groundwater management.
Important aspects being studied in this project include the sorption capacity for a variety of contaminants and the relative immobility of the sorbing phase under aquifer flow conditions.
Accomplishments
injection test at Monticello using clean water.
This project is being carried out by Chem-Nuclear Geotech, Inc. (Rust International), with the cooperation of the Monticello Remedial Action Project of the DOE Office of Environmental Restoration.
This effort is directly applicable to remediation of uranium contamination at the Monticello Mill site. Because uranium contamination in groundwater is prevalent at many DOE sites, this technology has widespread application. Other DOE sites with uranium contamination include UMTRA facilities, uranium groundwater contamination at Pantex, Fernald, the Rocky Flats Plant, Nevada Test Site, Y-12, and the Gaseous Diffusion Plant at Oak Ridge.
In addition, the application of this type of barrier may be appropriate for many different metals at DOE, DOD, EPA, and numerous commercial and industrial waste sites.
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This investigation will develop and test new barrier materials specifically for buried waste control. (see Figure 1.5). Tests will determine the long-term durability of the material, permeability to groundwater, ionic diffusivity, response to wet/dry cycling, and chemical resistance to acid, base, and organic solvent conditions that might occur at waste sites.
This study will also examine the effects of aggregate type and quantity on barrier performance. Inert aggregate substances such as clean sand and recycled glass used to produce the test specimens will be optimized to binder, geological, environmental and waste conditions.
Because the investigation will examine new applications of barrier constituents, regulatory issues affecting approval of barrier construction have been surveyed. This survey was a general overview of the regulatory concerns for emplacement of polymers and binders in soils, and included a specific focus on the use of thermoset resins.
Technology Needs
Sites with components that are not controllable with contaminant-specific sorbents will require barriers that prevent the movement of contaminated groundwater. Systems that use direct injection of barrier reagents as liquids, and subsequent in situ formation of the barrier, are preferred over those involving excavation.
Currently approved clay-based barriers may not be as effective as some synthetic polymers and resins. These agents may cement and seal sediments to form impermeable, chemically-resistant barriers to water movement. In some situations where in situ formation is not possible, and excavation costs are not prohibitive, barriers constructed with synthetic binders and an inert matrix provide an alternative. This investigation includes the search for appropriate matrix aggregates.
Accomplishments
All work on this project is currently being accomplished through the facilities of the Brookhaven National Laboratory's (BNL) Waste Management Group. Because one of the planned aggregate mixes involves recycled consumer glass waste, some cooperation with a municipal or commercial recycled glass supplier is envisioned.
Communication of the results of this investigation will be through an expert review panel workshop. Attendees will include BNL, DOE, and industry personnel. A summary report will be issued containing workshop results. Further technology transfer will include dissemination of study results at symposia and meetings of professional and industrial associations.
Potential demonstration sites are through the Buried Waste Integrated Demonstration, the Mixed Waste Landfill Integrated Demonstration, and the Underground Storage Tank (UST) Integrated Demonstration. Discussions at the Brookhaven Waste Management Group are identifying when and how the results of this investigation will be used.
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This investigation addresses the feasibility of frozen soil barriers (ground freezing technology) as a means of containing hazardous and radionuclide-contaminated soil in a non-arid setting. Because ground freezing has long been a civil engineering technique for ground control, water entry control, etc., this project is essentially a new application of an established technology. A series of holes are drilled and refrigerant is circulated, freezing the soil around the holes such that a confined volume is created, thereby preventing contaminant migration (see Figure 1.6).
The objective of this project is to design, install, and pre-test a soil freezing facility at an uncontaminated site. After successful completion of these objectives, a soil freezing technology demonstration would be performed to show construction of a containment system around an instrumented underground tank and associated piping. Data from this demonstration will be provided for the analysis of other possible field applications within the DOE complex.
A series of tests is planned, including:
A frozen soil barrier may meet containment needs by minimizing adverse impacts to the environment because:
Accomplishments
This project is a new start for FY93. DOE has selected Scientific Ecology Group, Inc. (SEG), to perform the technology demonstration. Negotiations on the scope of work are underway. The project is working on a completion of barrier installation and associated testing by the end of the third quarter of FY94.
Collaboration/Technology Transfer
Martin Marietta will provide project management, and SEG, Inc., will perform the design, construction and testing.
SEG, and its teaming partner, RKK Ltd., have significant experience in frozen soil applications from the civil engineering industry. In radioactive and hazardous waste applications, their design and supporting software have received substantial peer review by technical experts.
Assuming a frozen soil barrier can be successfully installed and tested, the technology could then be deployed at contaminated sites across the DOE complex. The initial barrier would also be available as a test bed/barrier, within which other researchers could test, develop and refine new treatment methods, perhaps even using actual hazardous materials.
Contaminated sites under the responsibility of other government agencies (e.g., Department of Defense) or private industry are also candidates for frozen soil barrier containment technology.
For more information, please contact:
This investigation addresses the feasibility of using frozen soil barriers (ground freezing technology) to contain hazardous and radionuclide-contaminated soil in an arid setting (see Figure 1.7).
The first phase is a lab-based investigation of containment aspects of frozen water in soil, including the behavior of associated solutes, transport mechanisms through unfrozen water films or pockets, mechanical effects such as heave, and other freezing-related processes.
Assuming favorable results from the lab-scale investigation, a frozen soil barrier will be installed at an uncontaminated site. Installation involves drilling to install pipes through which refrigerant is circulated. The holes are positioned to create a confined subsurface volume as the soil around the boreholes freezes. A critical aspect of this project is the successful, controlled addition (and removal) of water to the unsaturated subsurface to create the barrier. Water movement in response to 1) the negative pore pressures of the unsaturated zone, and 2) thermal gradients around freeze pipes complicates barrier formation beyond that of a saturated site. Upon completion, the project must also be able to remove water to prevent contaminant migration, should that be a requirement in the technology's future use at unsaturated contaminated sites. Assuming the successful addition of water, barrier integrity/performance would then be evaluated by means of tracer tests, monitoring of thermal conditions, and other suitable methods.
Furthermore, the barrier would then be available as a test bed within which other investigators could conduct studies of hazardous waste treatment technologies.
Technology Needs
Many of DOE's contaminant sources (e.g., landfills, dry wells, evaporation ponds, etc.) are located in arid climates and are typically far above the natural groundwater level. Frozen soil barriers are thought to be useful in providing containment at these sites. However, most experience with their hydraulic performance is associated with natural, fully saturated environments. Under arid conditions, performance may be affected by the need to first create full saturation, (i.e., achieve near-zero air porosity), then maintain this condition under the frozen state. This project will examine potential performance factors arising from arid site conditions and evaluate specific measures to mitigate or minimize adverse effects.
Accomplishments
Overall project management is the responsibility of DOE's Grand Junction Projects Office. The lab-based investigation of the behavior of water and solutes in frozen soil will be awarded to a subcontractor in late FY93. The design of the field installation and the subsequent testing is the responsibility of Chem Nuclear Geotech, Inc., a contractor to Grand Junction Project Office. Soil freezing and associated equipment are available commercially, but a subcontractor has not yet been selected.
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This investigation is examining a method of in situ emplacement of barriers beneath a waste site. The process begins with two horizontal drill holes curving down from the surface at one end of the area, passing beneath the waste, and returning to the surface at the other end. Steel cables are threaded through the holes and attached to a winch or tractor. At the opposite end, jet grouting equipment is attached to the cables and connected to grout pumps. The jet grouter itself is a hydraulically-driven injector-mixer which leaves a soil-grout in a slab about ten feet wide and 2 feet thick (see Figure 1.8).
The investigation is focusing on laying down a series of six strips, joining the edges into a contiguous sheet, and tying the horizontal barrier to surrounding vertical containment. Emplaced panels will be excavated and tested for gaps or zones of inadequate grout-soil mixing. Additional development will address widening the panels and emplacement of this type of barrier in soils with rock fragments that restrict grout tool movement and complete mixing.
Technology Needs
Temporary or long-term containment of mobile contaminants from existing waste sites requires effective surrounding barriers. Vertical barriers are relatively well-known from standard construction project work, but methods for building horizontal barriers in situ have not been developed. For old sites, the problem is to place a containment barrier without disturbing the waste. Any excavation of the waste represents additional health and regulatory problems that are expensive and difficult.
A technology that allows barrier construction with minimal waste management that is amenable to changes in barrier materials and works in a wide variety of soil matrices would be a powerful tool for site containment and remediation.
Accomplishments
This work is under the supervision of FERMCO and will be supported through collaboration by the technology owner, NUS Halliburton, with consulting support on grout and barrier materials from Brookhaven National Laboratory. Performance testing of the emplaced panels will be performed by the University of Cincinnati.
Potential users of this technology are widespread in the DOE complex and in the country. The waste sites and tanks at Hanford need a method for in situ emplacement of horizontal barriers. The Pits and Clearwell at Fernald are also potential users.
Because the need is so widespread, this technology is readily transferrable to containment problems outside DOE as well. Uncontrolled dump sites, leaking chemical and fuel storage tanks, and engineered but failing waste disposal facilities are additional candidates for this in situ containment system.
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