Introduction
The U.S. Department of Energy (DOE) is the federal agency responsible for the remediation of this country's nuclear weapons complex, a large network of industrial facilities for the research, production, and testing of nuclear weapons. This enormous undertaking currently is estimated to cost several hundreds of billion dollars over the next 75 years (U.S. Department of Energy, 1996).
Not all radioactive waste problems can be solved by excavating and treating wastes. Properly engineered containment systems can provide both interim isolation of contaminants, while remedial technologies are being developed, and longer-term isolation of those contaminants that will remain at DOE sites after remediation. Consequently, engineered containment structures (collectively referred to as ''barriers" in this report) such as surface caps and subsurface vertical and horizontal barriers will be needed as important components of remediation strategies.
The Committee on Remediation of Buried and Tank Wastes (hereafter, the "committee") was appointed by the National Research Council and has the general task of addressing critical generic and site-specific issues relevant to remediation of the environmental contamination from buried and tank-contained defense radioactive and mixed waste. Among the issues under study by the committee is the application of new and evolving remediation technologies and strategies. During its studies, the committee found that effective containment-in-place approaches are needed at the Hanford Site in Richland, Washington, and across the DOE complex (National Research Council, 1996). The committee also found that DOE was performing significant research, including prototype evaluations at facilities such as the Hanford Site in Washington and the Idaho National Engineering Laboratory, Idaho Falls. In addition, DOE has constructed and maintained surface barriers under the Uranium Mill Tailing Remedial Action (UMTRA) Project. Other entities have used barrier technologies successfully for many years to isolate waste materials and contaminated ground water and soil.
Consequently, the committee and representatives of the DOE Office of Environmental Restoration agreed that a workshop on containment barriers would be useful. Participants in such a workshop would include government researchers and contractors, as well as barrier designers and builders from the private sector. DOE and the committee cosponsored the workshop on August 13, 1995, in conjunction with the DOE ER'95 (Environmental Restoration 1995) Conference in Denver, Colorado.
The workshop program was designed to cover a wide range of barrier approaches using various materials, both natural and man-made, and different installation techniques. Information was presented on surface and subsurface barrier technologies being evaluated or used within the DOE complex and by other entities. Two overview presentations were followed by sessions on surface and subsurface barriers. Each session was completed by discussion with a panel of the presenters. The next day, the session chairs presented a summary to the attendees of ER'95. The program for the workshop is included as Appendix B, and workshop participants are listed in Appendix C.
