Geology
The formation that makes up Yucca Mountain was created by several large eruptions from a caldera volcano and is composed of alternating layers of ignimbrite (welded tuff), non-welded tuff, and semi-welded tuff. The tuff surround the burial sites is expected to protect human health as it provides a natural barrier to the radiation. It lies along the transition between the Mohave and the Great Basin Deserts.
The volcanic tuff at Yucca Mountain is appreciably fractured and movement of water through an aquifer below the waste repository is primarily through fractures. While the fractures are usually confined to individual layers of tuff, the faults extend from the planned storage area all the way to the water table 600 to 1,500 ft (180 to 460 m) below the surface. Future water transport from the surface to waste containers is likely to be dominated by fractures. There is evidence that surface water has been transported down through the 700 ft (210 m) of overburden to the exploratory tunnel at Yucca Mountain in less than 50 years.
Some site opponents assert that, after the predicted containment failure of the waste containers, these cracks may provide a route for movement of radioactive waste that dissolves in the water flowing downward from the desert surface. Officials state that the waste containers will be stored in such a way as to minimize or even nearly eliminate this possibility.
The area around Yucca Mountain received much more rain in the geologic past and the water table was consequently much higher than it is today, though well below the level of the repository.
Read more about this topic: Yucca Mountain Nuclear Waste Repository