Summary of revised potentiometric-surface map for Yucca Mountain and vicinity, Nevada

The revised map for the potentiometric surface of the uppermost saturated zone in Tertiary volcanic rocks at Yucca Mountain, Nevada, is based mainly on 1988 water levels. Refinement of the water-level corrections has increased understanding of the area immediately east-southeast and hydrologically downgradient of Yucca Mountain. This small-gradient area is a nearly horizontal surface which corresponds to the likely direction of ground-water flow from Yucca Mountain - east-southeast. To the west of Yucca Mountain, water levels are approximately 45 m higher than those in the small-gradient area, and to the east of the northern part of Yucca Mountain water levels are approximately 300 m higher than those in the small-gradient area. Water levels are higher to the west of Yucca Mountain apparently because of a barrier to ground-water flow formed by the Solitario Canyon fault and a splay of the fault, and water levels are higher to the north apparently because of a semi-perched ground-water system.