Waste-containment sites number in the hundreds of thousands throughout the world as a result of past and continuing industrial, municipal, and military activities. Within the United States alone, recent records of the United States Environmental Protection Agency (USEPA) indicate the existence of more than 200,000 contaminated sites, a large fraction of which involve or need waste containment. In addition to contaminated sites and facilities, a large waste-generation inventory comprises billions of metric tons of metal mining and processing wastes, oil and gas processing wastes, industrial wastes, municipal wastes, and solid wastes from electric power generation stations. At the Hanford site, which had been a plutonium production site for 50 years, approximately 7,600 cubic meters of actinides, as well as 1.2 million cubic meters of low-level radioactive wastes, are buried.
It is not feasible to chemically or biologically clean up all contaminated sites because of excessive costs (including opportunity costs). Furthermore, the complexities of both the subsurface geohydrology of contaminated sites and the lack of field-scale cleanup technologies that can apply mechanisms proved at the bench scale for some persistent contaminants to field scale make it infeasible to implement cleanup programs as the sole means of managing contaminated sites. With respect to solid waste management, recycling has not kept pace with generation rates. Consequently, waste storage in containment systems will remain as a waste-management option for the foreseeable future. Among these systems are landfills, waste piles, covers and liners, grout curtains, slurry walls, reactive walls and beds, concrete tombs, and radioactive waste repositories. For these systems, the primary design function is minimizing the rates of contaminant release into the environment for service lives that range from about 10 years to 1,000 years. The performance of this function requires that the structural integrity of these systems be maintained for very long time periods. Considering the high uncertainties associated with system performance over very long time spans within which transient stressors such as floods and earthquakes may affect some facilities, the challenge is to develop effective approaches to designing, building, operating, monitoring, and maintaining waste-containment systems.
With respect to design, optimal combinations of material characteristics, component dimensions, and system configuration for specific categories of waste and site geohydrological conditions can increase system reliability against damage and failure. Monitoring implemented systems provides an opportunity for identifying faulty components and implementing remedial measures. By analogy to medical practice, doctors emphasize early diagnosis of ailments to improve the chances for successful treatment and to minimize the cost of treatment. Often, noninvasive techniques are used to probe the body, examine conditions at critical points and organs, and fix problems before they become irreparable. This approach enables physicians to better understand aging and disease processes for better diagnoses and preemptive and corrective action. In contrast, the primary methods of monitoring containment system performance are currently still focused on observing above-ground components and detecting contaminants in groundwater. Unfortunately, the internal condition of containment systems is rarely tracked to discern deterioration or failure until it is too late. Observing contaminants in groundwater implies that the barrier components of the containment system have already malfunctioned and that the system has already failed (the “barrier” patient has already died!). Consequently, the cleanup of contaminants that have already spread will be expensive or possibly impractical.
Advances in sensor development, data acquisition, and data broadcast systems have expanded opportunities for early detection of barrier component deterioration and displaced contaminants within and outside containment systems. Data acquired from advanced monitoring systems have high utility in defining the growth or decay of contaminant source terms in risk assessment. Some models have been developed by agencies and technical organizations for source term prediction. Examples of such models include the Disposal Unit Source Term (DUST), developed by Brookhaven National Laboratory (United States); Framework for Risk Analysis in Multimedia Environmental Systems (FRAMES), developed by the Pacific Northwest National Laboratory (PNNL); and the Multimedia Environmental Pollutant Assessment System (MEPAS). Data from sensor networks can also be fed into systems within a framework for improving the design, implementation, and management of waste-containment systems, as illustrated in Fig. 1. These systems will advance the capacity to address the issues raised in the following questions about various aspects of waste-containment system implementation and management.
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What comprehensive analytical frameworks exist for addressing the long-term performance of multicomponent systems, and how can such frameworks be adapted to waste-containment systems? Consider reliability concepts, system damage concepts, fault trees, and others.
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What alternative criteria exist for determining both the structural failure and functional failure of components of a multicomponent system to the functional failure of the multicomponent waste-containment and treatment system?
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What are the most significant damage scenarios, events, mechanisms, and processes? How do they affect the contaminant generation and transport characteristics of barriers and the entire containment system, and how can these factors be captured quantitatively in long-term system performance models? How may the importance of different processes evolve with time? If we focus only on failure effects that are manifest at short times, are we missing key phenomena that can become more important later in barrier life? How might these processes combine so that the sum is worse than each process individually? Effects that should be considered relate mostly to freeze-thaw, temperature fluctuation, flood damage, seismic damage, root and rodent penetration, and photodegradation.
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How can quantitative frameworks be developed for establishing linkages among contaminant release source terms (through damage or continuous release), exposure assessment models, compliance, limits, and monitoring needs?
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How can waste-containment and treatment system performance models be used in facility maintenance planning, environmental and human exposure assessment, and monitoring plan development?
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Since barriers degrade before the end of their design lifetimes, how do we manage the barriers? For example, how do we determine through monitoring and understanding barrier failure modes and effects whether this degradation invalidates the design lifetime/performance assessment and therefore whether the barrier should be repaired or improved? What failure modes and effects must be monitored? If repair or improvement is needed, how well can monitoring pinpoint the location of barrier failure? How early can degradation be observed?
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Are there barrier damage/system concepts and adequate barrier failure modes and effects understanding that could lay the foundation for taking partial credit for barrier performance after the end of the design lifetime?
Fig. 1. Use of system monitoring and knowledge of dynamic processes for better design and management of waste containment systems
Many recent fundamental research efforts and field projects have provided information that is useful with respect to addressing the issues raised in the preceding.
Analytical methodologies and concepts from other physical science, engineering, and social science fields need to be adapted for use in waste-containment system improvement and performance prediction programs. The technical papers included in this special edition of the ASCE Practice Periodical of Hazardous, Toxic, and Radioactive Waste Management on “Innovative Barrier Systems for Waste Containment” is a movement in that direction.
About This Special Issue
In their editorial in this special issue, Hilary I. Inyang, Steve Piet, Robert Breckenridge, and Irene Lo have outlined approaches that can be adopted to enhance the cost-effectiveness of waste-containment systems. The editorial is followed by more detailed discussion of design principles and concepts around the design of caps. The analyses written by Piet, Breckenridge, Jacobson, White, and Inyang address covers in various geohydrological environments.
Evapotranspiration caps have gained importance in the containment of wastes in dry climates. Two papers written by research teams affiliated with the Idaho National Laboratory (INL) in Idaho Falls deal with this issue. Through collaborative research with INL, Amy Forman of S. M. Stoller Corporation and Jay Anderson of the Center for Ecological Research and Education, Idaho State University, performed field experiments on evapotranspiration cap designs. Their results are presented in this special edition. Capillary barriers that regulate the transmission of moisture to buried wastes operate at various hydraulic flow regimes under loads that are defined by their design configurations and geotechnical environment. Through collaborative research by researchers affiliated with the Global Institute for Energy and Environmental Systems (GIEES) of the University of North Carolina at Charlotte and INL, the long-term degradation of drainage layers of capillary barriers has been investigated experimentally. The researchers (Vincent Ogunro, Robert Podgorney, Hilary I. Inyang, Steven Piet, and Mutiu Ayoola) present their results in a paper included in this special issue. Site factors, including geodynamic events, are parameters that factor into the long-term performance of waste-containment systems. In the southeastern United States where sinkholes develop in karst terrains, damage to facilities can be mitigated through implementing ground stabilization measures and reliable designs. In their paper, Shiou-San Kuo and Karishma Desai of the University of Central Florida and Lymari Rivera of the City of Hallandale Beach, Florida, present detailed design aids for developing municipal solid-waste landfill liner systems where sinkholes occur in the subsurface. For damage that may occur in containment systems in seismic regions, Mutiu Ayoola, Hilary I. Inyang, and Vincent Ogunro present a review of recent analytical advances.
The functional performance requirements of waste-containment systems depend partially on the volume and characteristics of the wastes that they contain. Although much focus has been placed on the hydraulic control capacity of barriers, radiation control is a critical issue at some contaminated sites. In this special issue, Hilary I. Inyang, Paul Wachsmuth, and Gustavo Menezes of GIEES have developed and presented simplified design equations for ground surface barriers that can reduce the intensity of gamma radiation emitted by radionuclides. They have named these barriers “georadiological or georad barriers.” For these and other barriers, material characteristics are very significant with respect to the performance of design functions. Effort on the improvement of barrier materials is ongoing in industry and research institutions. One of these efforts is research on enhancing barrier performance through the use of biofilms. In this special edition, John Daniels and Raghuram Cherukuri, who are affiliated with GIEES and the Department of Civil Engineering of the University of North Carolina at Charlotte, report on the results of their feasibility studies on the use of exopolymeric substances (EPS) to improve the textural and hydraulic characteristics of two barrier soils.
As a contribution to efforts to analyze and monitor the performance of waste-containment systems in the field, Jon Luellen and Jason Brydges of URS Corporation, New York, have used the Hydrologic Evaluation of Landfill Performance (HELP) model to evaluate alternative designs of cover systems for a radiologically contaminated site. Use of their results and others that are exhibited in this special issue will be beneficial to waste containment and storage projects.
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Practice Periodical of Hazardous, Toxic, and Radioactive Waste Management
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