The seepage rate is important because abundant water would corrode the waste canisters and carry the radioactive isotopes down to the water table, where they could spread and eventually contaminate drinking water. By law, the repository and the specially designed canisters must limit leakage for the next 10,000 years. This indicates that little liquid is flowing through the rock today, says Fabryka-Martin. During the last ice age, however, the region received more rain than it does now. Next year, the Department of Energy, which oversees the Yucca Mountain project, will issue a preliminary assessment of the site's suitability for storage.
Opponents view the new measurements as a serious blow to the planned repository.
Russell L. Patterson, a hydrologist with the Energy Department, disagrees. Scientists had acknowledged the possibility that water could move through so-called fast pathways, so the new data were not totally unanticipated, he says. In fact, he views the movement of water through the rock as a potential benefit. Last week's provisional EPA approval for WIPP brings the New Mexico repository one step closer to opening, which could take place as early as May 1998. The laws governing hazardous waste have been challenged often in court, and opponents of WIPP may follow legal paths to block the facility's opening.