Introduction
The Environmental Restoration Program of the U.S. Department of Energy, Nevada Operations
Office, was developed to investigate the possible consequences to the environment of 40 years of
nuclear testing on the Nevada Test Site. The majority of the tests were detonated underground,
introducing contaminants into the ground-water system (Laczniak and others, 1996). An
understanding of the ground-water flow paths is necessary to evaluate the extent of ground-water
contamination. This report provides information specific to Yucca Flat on the Nevada Test Site.
Critical to understanding the ground-water flow beneath Yucca Flat is an understanding of
the subsurface geology, particularly the structure and distribution of the pre-Tertiary rocks, which
comprise both the major regional aquifer and aquitard sequences (Winograd and Thordarson, 1975;
Laczniak and others, 1996). Because the pre-Tertiary rocks are not exposed at the surface of Yucca
Flat their distribution must be determined through well logs and less direct geophysical methods
such as potential field studies.
In previous studies (Phelps and others, 1999; Phelps and Mckee, 1999) developed a model
of the basement surface of the Paleozoic rocks beneath Yucca Flat and a series of normal faults that
create topographic relief on the basement surface.
In this study the basement rocks and structure of Yucca Flat are examined in more detail
using the basement gravity anomaly derived from the isostatic gravity inversion model of Phelps
and others (1999) and high-resolution magnetic data, as part of an effort to gain a better
understanding of the Paleozoic rocks beneath Yucca Flat in support of groundwater modeling.
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First posted April 18, 2000
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