DVRFS PROJECT
BACKGROUND
The U.S. Geological Survey, in cooperation with the U.S. Department of Energy (DOE) and
other Federal, State, and local agencies, is evaluating the geohydrologic characteristics
of the Death Valley regional ground-water flow system. The Death Valley regional
ground-water flow system is one of the larger flow systems within the Southwestern
United States and includes in its boundaries the Nevada Test Site (NTS), Yucca Mountain,
and much of Death Valley.
Scientists from the USGS are evaluating the geologic
and hydrologic characteristics
of Yucca Mountain in order to assess if it can meet specified repository-performance
criteria. A national, federally-operated, mined-geologic, high-level nuclear waste
repository has been mandated by law for the isolation of spent nuclear fuel from
energy facilities across the country. Yucca Mountain, on and adjacent to the Nevada
Test Site (NTS), has been chosen as the potential site for this repository.
The DOE and the U.S. Department of Defense (DOD) conducted various types of
underground
nuclear tests at the NTS in southern Nevada between 1951 and 1992.
These tests contaminated ground water with radionuclides beneath some parts of the NTS.
Because of the potential for radionuclides to be transported by ground water away from
the repository and the underground test areas to the accessible environment, ground-water
flow-system dynamics in the area must be characterized.
As part of support to DOE , three-dimensional, steady-state and transient ground-water
flow models of the Death Valley flow system, which includes the Yucca Mountain area
and the NTS, are being developed.
These models will assist in the:
·
Definition of boundaries of the subregional and local flow
systems;
·
Characterization of regional 3D ground-water flow paths;
·
Definition of locations of regional ground-water discharges;
·
Estimation of magnitudes and rates of regional subsurface
flux;
·
Evaluation of potential and existing anthropogenic effects
on ground-water flow;
·
Characterization of potential impacts of the regional
carbonate aquifer on subregional and local flow components; and
·
Determination of potential effects of regional geologic
structure on the flow system.
OBJECTIVES
Develop a
comprehensive 3D hydrogeologic framework and ground-water flow model of
the Death Valley region. The
model will describe flow-paths and magnitude of flow in the ground-water
system.
APPROACH
The Death Valley regional ground-water flow system is being simulated using a three-dimensional
steady-state simulation that incorporates a nonlinear least squares regression
technique to estimate aquifer variables.
The numerical modeling program MODFLOW 2000 is being used to create a
finite-difference model consisting of 160 rows,
194 columns, and Sixteen layers.
The grid cells are oriented north-south and are of uniform size, with
side dimensions of 1500 meters.
The required model parameter
values are supplied by discretization of the three-dimensional
hydrogeologic framework model and digital representations of the remaining
conceptual model components. The
three-dimensional simulation supports the analysis of interactions between
relatively shallow local and subregional flow paths and the deeper
dominant regional flow paths controlled by the carbonate aquifer.
RELEVANCE AND BENEFITS
Societal relevance of this investigation includes the development of three-dimensional
hydrogeologic modeling tools that will be used to assess the feasibility of isolating
nuclear waste from the accessible environment for over 10,000 years and the migration
of contaminants from nuclear testing. The resulting flow model also serves as important
water management tool for the Death Valley region.
