Multi-Dimensional Modeling of Unsaturated Flow in the Vicinity of Exploratory Shafts and Fault Zones at Yucca Mountain, Nevada

Modeling studies were conducted to determine the potential effects of exploratory shafts on moisture distribution in the vicinity of an exploratory shaft facility, and the potential for development of perched water table conditions near fault zones in the unsaturated zone at Yucca Mountain, Nevada. Simulations were performed using PORFLO-3, an integrated finite-difference computer code designed to simulate fluid flow, heat transfer, and mass transport in variably saturated porous and fractured media. Simulation results suggest that the modified permeability zones around exploratory shafts and faults may act as conduits for preferential flow of water in the welded tuff units at Yucca Mountain when locally saturated conditions and fracture flow occur. However, episodic pulses of water were damped out with depth in the model simulations so that moisture contents at the level of the proposed repository remained relatively unaffected. These simulation results also indicate a potential for lateral flow in the units overlying the proposed repository horizon. Perched water tables did not develop under the simulated conditions.