Fluid flow in partially saturated, welded-nonwelded tuff units

Abstract

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 mm/yr, pulses expressed as short durations separated by periods up to 5000 yr, most effects of the transient infiltration pulses were damped by the Paintbrush nonwelded unit. The effects of eastern tilting of the units at Yucca Mountain on the steady state fluid flow distribution were studied using a two-dimensional model. Ghost Dance Fault was modeled as a seepage face. Under the expected flux conditions, saturation increased just to the west of the fault, but the water did not enter the fault with the seepage boundary condition.