New Evidence of Rapid Water Movement Supports Disqualifying Yucca Mountain

In late April 1996, DOE released a report by Los Alamos National Laboratory researchers that documented elevated levels of Chlorine-36 in five of the faults uncovered by the Tunnel Boring Machine within the proposed repository block. These elevated Chlorine-36 levels could only have come from the atmospheric nuclear tests conducted in the Pacific Ocean less than 50 years ago. To get 600 or more feet below the surface where they were discovered in less than 50 years, this radioactive isotope had to have been carried there by water flowing rapidly downward from the ground surface - prima facie evidence that fast groundwater pathways exist at Yucca Mountain. The significance of this finding is that DOE's own siting guidelines, and the Nuclear Regulatory Commission licensing regulations, require a site to be disqualified if it is shown that groundwater travel time through the repository to the accessible environment (e.g., the aquifer) is shorter than 1,000 years. The Chlorine-36 discovery confirms earlier findings of elevated tritium levels in perched water bodies encountered previously by the U.S. Geologic Survey in boreholes below the repository level. Tritium is another radioactive element that was created by atmospheric weapons tests and, therefore, dates water in which it is found at no more than 50 years.

While this finding means it is impossible for the water flow rate in faults or fractures to be slower than about 50 years, it could actually be much faster. For example, it is not known whether the Chlorine-36 was transported to the repository horizon in 1 year, 2 years, 5 years, or 49 years after the atomic test that generated the radioisotope. Regardless, the flow of water through the proposed repository is very rapid, something Nevada scientists have contended for years because of the highly fractured geology and the rapid pathways such conditions create.

DOE contends that it is too early to determine the significance of the Chlorine-36 and related findings and has indicated that the regulations governing site disqualification may need to be changed since they fail to permit evaluation of groundwater flow rates in light of other site characteristics. What the new finding means, however, is that licensing a Yucca Mountain repository will be even more difficult and more contentious, and may not be possible at all unless regulations are changed to be more lenient.

State of Nevada researchers have long contended that water flow rates from the ground surface through the proposed repository block into the water table are substantially faster than the 1,000 years required by the siting guidelines and NRC regulations. In comments on DOE's draft Environmental Assessment for the Yucca Mountain site as far back as 1984, Nevada Nuclear Waste Project Office staff noted that DOE's own data showed that water flow through fractures at the site was very rapid, and that the site would likely not meet DOE's own guidelines. In 1989, Governor Miller wrote to Energy Secretary Watkins recommending that the Yucca Mountain site be disqualified based, among other things, on the evidence of rapid water movement.

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