Preliminary Numerical Simulations of Groundwater Flow in the Unsaturated Zone, Yucca Mountain, Nevada

摘要

Numerical simulations of the natural state of the unsaturated zone underlying Yucca Mountain, Nevada, were performed. The hydrogeology at Yucca Mountain is characterized by a fluid flow through heterogeneous, anisotropic, fractured tuff in an arid environment. The purpose of the study is to examine the general groundwater-flow patterns computed on the basis of the available data and to examine ideas contained in a proposed conceptual hydrologic model of the site. The model simulates two-dimensional liquid-water flow in a vertical cross section extending from the ground surface to the water table at a depth of about 650 m. Various fluxes representing the net infiltration were specified at the surface and the steady-state flux, liquid-saturation distribution, and matric-potential distribution were computed. The results indicate that because of the dip of the stratigraphic units and because of their hydraulic properties, a significant proportion of the flow above and/or below the proposed repository horizon is diverted laterally into a permeable fault zone. The magnitude and location of the lateral flow depend upon whether matrix-flow or fracture-flow conditions are assumed for the highly fractured units, upon the flux specified at the ground surface, and upon the hydraulic properties assigned to the fault zone. Various cases were considered to examine the liquid-water flux through the proposed repository unit; all of the results are controlled by poorly known hydraulic parameters such as the characteristic curves. (ERA citation 11:041875)