EVALUATION OF A CONCEPTUAL MODEL FOR SATURATED ZONE FLOW AND TRANSPORT

摘要

Estimates of contaminant travel time through the saturated zone (SZ) downstream of the proposed Yucca Mountain HLW repository are dependent on the conceptual model for where and how flow occurs within the SZ. Much of the SZ immediately downstream of Yucca Mountain is in fractured tuff, where the tuff matrix itself is relatively porous. The current conceptual model for SZ flow and transport assumes all flow is in a series of thin flowing intervals separated by approximately 20 meters of intact rock. This conceptualization provides for minimal transfer of contaminants between water in the fractures and water in the near-stagnant matrix. An alternative approach suggests that flow occurs in a network of closely spaced fractures, such that much more fracture/matrix interaction is possible. The implication for average contaminant travel-time estimates through the SZ of choosing one approach versus the other is significant.