THE U.S. GEOLOGICAL SURVEY'S ACTIVITIES RELATING TO LONG-TERM DISPOSAL OF HIGH-LEVEL RADIOACTIVE WASTE

The U.S. Geological Survey has been a proponent for geologic disposal of high-level radioactive waste for more than 30 years, and we remain convinced that this avenue provides the only long-term approach for dealing with long-lived radioactive waste. Our scientists have worked both in identifying sites to be investigated and in characterizing sites selected as potential candidates. In so doing, we have worked closely with scientists from other agencies and academia to develop and apply many of the concepts reviewed in this session.

About a year ago, the USGS submitted a letter in support of the site recommendation for Yucca Mountain, Nevada, based upon our understanding of the inherent attributes of the site. Physical assets of the site include (1) relatively uncomplicated geology; (2) lack of economic mineral or energy deposits; (3) ease of excavating stable tunnels; (4) arid climate and resulting very low rate of infiltration; (5) small percentage of infiltrating water that would actually seep into drifts; and (6) free drainage, through fractures on the floor of the drifts, of any water that enters the tunnels. Additional positive attributes are the natural, passive ventilation of the mountain; abundant zeolites below the repository horizon, which tend to retard the movement of certain radionuclides; and the presence of an extremely thick unsaturated zone, which enhances the opportunity for long-term monitoring and retrieval of the waste, should it become necessary.

Although the USGS favors geologic disposal of high-level radioactive waste and notes many positive attributes at Yucca Mountain, we fully recognize that no site will be perfect. At Yucca Mountain, and perhaps at most other potential sites, there are geologic hazards that need to be addressed. Although the local geology of Yucca Mountain is relatively uncomplicated, the unsaturated zone and regional hydrologic systems are complex, particularly when future conditions are considered. The USGS endorses continued study of the site as part of a step-wise decision-making process that would allow future decision-makers to select alternative options, if necessary, based upon additional information, different societal needs, or changing priorities.