Los Alamos National Laboratory
Description
The subject technologies focus on the rapid implementation of near-surface barriers, biotreatment, and post-closure monitoring technology. They integrate water-permeable and biologic barriers that chemically capture and/or degrade contaminants without significantly altering the natural water flow. Specific evaluations are being done for gel barrier materials, enhancement of natural biologic communities, chemical tracer approaches, and remote monitoring of the hydrologic systems.
Two different potential applications of the barrier technologies are being evaluated. The first is the use of barriers for chemical confinement for in-trench treatments with a leach system or an in-place bioreactor. The second is the integration of permeable reactive barriers and petroleum reservoir gel/foam/polymer technology with grout or clay slurry walls to direct horizontal surface and subsurface water flows around a contaminated area.
Barrier and post-closure monitoring tests are being conducted 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, permeable reactive barriers and in-place bioreactors.
Permeable, Reactive Barriers. These barriers allow the passage of water while prohibiting the movement of contaminants by employing such agents as chelators (ligands selected for their specificity for a given metal), sorbents, microbes, and others. In Department of Energy (DOE) sites where multiple contaminants are ubiquitous, multicomponent barriers need to be evaluated. Field-scale experiments were constructed using natural sand with the permeable barriers consisting of zeolite + silica gel + sand, bentonite + Al crosslink polyacrylimide + sand, and peat + Al crosslink polyacrylimide + sand .
The reactive barriers could be designed (1) to remain in place as permanent or semi-permanent installations; (2) to be removed and replaced periodically, thus serving as a component of the remediation process; and/or (3) to be used as part of the post-closure monitoring system in which the appearance of a contaminant in the barrier would then serve to warn of impending contaminant migration.
In-Place Bioreactors. This technical approach uses the capabilities of native bacteria for degrading hazardous organic compounds in a cost-effective, publicly acceptable manner. The capability can be managed to provide prolonged treatment, as well as treatment of relatively short duration. In addition to full-scale site, biodegradation has significant near-term potential as an effective containment strategy. Thus, evaluation of approaches to managing biologic communities on the margins of a site, in combination with other barrier approaches, will provide both significant information for both limitation of contaminant transport and full-site cleanup.
Post-closure monitoring. The field experiments have focused on evaluation of water saturation and chemical transport. Comparison of established neutron probe measurements of water saturation in arid soils with developments in Time Domain Reflectometry probe systems is being used to evaluate opportunities for automated and more detailed characterization. Chemical transport is being evaluated through the use of contaminant and chemical tracer materials. Application of tagged tracers allows evaluation of both barrier system effectiveness and potential contaminant transport pathways or eminent arrival.
Tracers for the permeable barrier experiments included low concentrations of common anions (e.g., bromide), soluble organic acids, semivolatile organic acids, fluorescein, chromium, and EDTA. The tracer/pseudo-contaminant for the bio-barrier experiments focused on toluene, labeled with carbon-13, to allow specific characterization of transport and biodegredation processes as a function of plant cover and fertilization.
Technical Performance Data
The permeable barriers are being designed to operate unattended with minimal maintenance for long periods of time (i.e., years). However, periodic inspections will be required because these enhanced barriers might fail because of cracking. Since the barriers are passive, no power is required for their operation.
The post-closure monitoring system will be autonomous with minimal energy consumption. Thus, batteries can be used as the power source.
Cost. The field tests at Los Alamos National Laboratory (LANL) that are scheduled for completion in early 1994 had a start-up cost of $1.2M and an operations/maintenance cost of $670K in FY93. Life cycle costs for operational systems have not been estimated, but are expected to be 5 to 10 times less than excavation.
Projected Performance
Quantified performance data do not seem to have been estimated for production systems. However, significant improvements are anticipated in both operational costs and acceptance by public and regulatory communities.
Waste Applicability
These barrier technologies are primarily intended for in situ treatment/containment of soluble metals and organics in arid soils.
The contaminants will either be degraded or retained in a concentrated form by the barrier material. The barrier could provide permanent containment for the relatively benign residues or provide a decreased volume of the more toxic contaminants for subsequent treatment.
Status
Evaluation of the currently installed systems should be completed in early 1994 (Ref. 1). The first barrier and monitoring systems were installed in 1992 and tracer tests, which would include the effects of seasonal changes in the environment, were scheduled for completion in 1993 (Ref. 2). Approximately two additional years would be required to test and evaluate each additional barrier system.
Regulatory Considerations
Closure and post-closure monitoring will be required under Resource Conservation and Recovery Act (RCRA), Comprehensive Environmental Response Compensation and Liability Act (CERCLA), Superfund Amendments Reauthorization Act (SARA), and Department of Energy (DOE) Order 5820.2A. For hazardous chemical sites, the required post-closure monitoring period is 30 yrs. For radioactive sites that have been closed, DOE Order 5820.2A requires monitoring and maintenance of the site for 100 yrs.
Potential Commercial Applications
The components of the barrier and monitoring systems that are currently being field tested have all been obtained from commercial vendors. Thus, these technologies can lend to full commercialization.
Furthermore, chemical and petroleum companies are now actively applying the proposed types of permeable barrier and biotechnological technologies in enhanced oil recovery operations.
Baseline Technology
Baseline technologies currently being used by the DOE include grouts, clay slurries, and cements for pure hydrologic barriers, landfill caps for the biotreatment systems, and monitoring well characterization for water-saturation and contaminants during the post-closure monitoring approaches. However, these barriers are all subject to cracking. In addition, by design, they restrict water transport out of the contained area and often require active treatment and disposal systems to maintain a stability.
Intellectual Property Rights
Patent Ownership: To be determined.
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References
Go to the Remediation Technology Profiles Index