DEVELOPMENT OF A 3-DIMENSIONAL SITE-SCALE MODEL FOR THE UNSATURATED ZONE AT YUCCA MOUNTAIN, NEVADA

A three-dimensional model of moisture flow within the highly heterogen eous, porous and fractured tuffs of the unsaturated zone at Yucca Moun tain is being developed. This site-scale model covers an area of about 30 km2 and is bounded by major faults to the east and west. A detaile d numerical grid has been developed based on the locations of borehole s, on the spatial distribution of different infiltration zones, hydrog eological units and water level data, and on the offset of the volcani c tuffs due to major faults. Hydrogeologic contour-and isopachs maps, are presented for the different infiltration zones, and for the base o f the Tiva Canyon, the Paintbrush, and the Topopah Spring hydrogeologi cal units. One- and two-dimensional simulations have been performed us ing the TOUGH2 computer code to test the geometry and the accuracy of the model-grid, which consists of about 5000 gridblocks distributed am ong 17 non-uniform vertical layers representing the four main hydrogeo logical units of the unsaturated zone.