Hydrologic mechanisms governing partially saturated fluid flow in fractured welded units and porous non-welded units at Yucca Mountain
A discrete fracture, porous matrix model and a composite medium model were used to study hydrological responses to cycles of pulse infiltration at Yucca Mountain, a potential site for a nuclear waste repository. The pulses were applied to fractures at the top of a vertical column composed of alternating layers of welded and nonwelded volcanic tuff. For average infiltration rates of 0.1 to 0.5 mm/yr, pulses expressed as short durations separated by periods up to 5000 yr, the transition from partially saturated conditions to fully saturated conditions and the corresponding onset of fracture flows occur in the top Tiva Canyon welded unit. As water moves down into the Paintbrush nonwelded unit, most effects of the transient infiltration pulse are damped during the first few thousand years. The responses of the underlying Topopah Spring welded unit to the pulses exhibit only small changes in saturation, pressure, and potential from the steady-state values. In addition to the downward motion, some of the infiltrating water may move laterally. Lateral flows in the column model are caused by an assumed fixed gradient in the horizontal direction, corresponding to the eastward dip of the bedding planes. For 0.1 mm/yr average infiltration cases which the fixed-gradient approximation is applicable under steady-state conditions, the infiltration pulses prefer to move essentially downward with a small fraction of water moving laterally.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 60024
- Report Number(s):
- SAND-85-7114; ON: DE87003587
- Resource Relation:
- Other Information: PBD: Oct 1986
- Country of Publication:
- United States
- Language:
- English
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