The U.S. Department of Energy's Waste Isolation Pilot Plant, located in Permian-age bedded salt in southeastern New Mexico, is the nation's only operating deep geologic repository for radioactive waste. The disposal facility, 2500 feet below the land surface in sparsely inhabited rangeland east of Carlsbad, is currently disposing of transuranic waste generated by activities related to national defense. Surface-based site characterization work began in 1974, and continued in parallel with excavation and subsurface testing beginning in 1981. Federal law assigned regulatory authority for the site to the U.S. Environmental Protection Agency in 1992. The DOE submitted a compliance certification application to the EPA in 1996, the EPA issued a final certification in 1998, and waste shipments began in 1999.

Many aspects of the WIPP experience are potentially relevant to the siting and possible licensing of other geologic repositories in the U.S., including Yucca Mountain. Long-term regulatory requirements for the WIPP are similar to those for Yucca Mountain, particularly in their emphasis on probabilistic analysis and the consideration of uncertainty in estimates of 10,000-year performance. Although details of site characterization must be determined by the local geology, the overall strategy toward scientific research employed at the WIPP is broadly applicable elsewhere. Early phases of site characterization emphasized understanding and reduction of uncertainty in all aspects of the system. As understanding matured, research focussed on those areas where remaining uncertainty showed the greatest impact on performance. The DOE's certification application and the EPA's subsequent certification decision explicitly acknowledge residual uncertainty in the understanding of long-term performance, and conclude that the site meets applicable standards and provides robust protection to public health and the environment. Confidence in this conclusion comes from multiple sources, including independent technical review, thorough documentation, and adherence to a formal regulatory process.