Three-dimensional hydrological and thermal property models of Yucca Mountain, Nevada Page: 4 of 351
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Unlimited Release Distribution
Printed November 1997 Category UC-814
Three-Dimensional Hydrological and Thermal Property
Models of Yucca Mountain, Nevada
Christopher A. Rautman
Sean A. McKenna
Sandia National Laboratories
P O. Box 5800
Albuquerque, New Mexico 87185-1324
Three-dimensional heterogeneous, yet spatially correlated models of selected rock matrix properties
have been created using geostatistical conditional simulation for three major rock units present within the
unsaturated and shallow saturated zones in the vicinity of the potential nuclear-waste repository site at
Yucca Mountain, Nevada. The three rock units are all of Miocene age, and they include the nonwelded and
principally vitric materials of the upper Paintbrush Group below the densely welded portion of the Tiva
Canyon Tuff (PTn model unit), the densely welded and principally devitrified rocks of the Topopah Spring
Tuff (unit TSw), and the nonwelded to partially welded and variably zeolitized materials of the Calico
Hills Formation and Prow Pass Tuff unit (CH-PP). The rock properties modeled include porosity, bulk
density, and saturated hydraulic conductivity for each unit, and thermal conductivity for the TSw model
unit. These property models synthesize the vertical and lateral variability of porosity measurements
obtained through both laboratory measurement of core samples and down-hole petrophysical observations
from across the entire Yucca Mountain site area. The models of hydraulic conductivity, bulk density, and
thermal conductivity are based on the use of cross-variable correlations with porosity, in which the spatial
continuity patterns of the different rock properties are coregionalized. The simulated models are intended
principally for use as input to numerical modeling of ground-water flow and radionuclide transport, includ-
ing coupled thermal and hydrologic processes. The suites of statistically similar simulated models have
been summarized as "expected-value" (E-type) models similar to those that would result from application
of an interpolation algorithm. This post-processing of replicate simulations has also allowed an assessment
of the uncertainty in the prediction of spatially varying rock properties that results from less-than-exhaus-
tive site characterization.
The simulated models indicate substantial material-property heterogeneity, both vertically and later-
ally and that this geologic heterogeneity exists on several spatial scales. The use of quantitative spatial cor-
relation through the modeling process, combined with the influence of actual measurements of physical
properties such as porosity, induces small-scale, "layered" and zonal heterogeneity that is not dependent
upon the arbitrary distinction of numerous individual and discrete "stratigraphic" units whose lateral conti-
nuity is uncertain. The modeling methodology makes use of the constraining influence of broadly deter-
ministic geologic processes, while at the same time respecting geologic knowledge from both modern and
other ancient analogue environments that indicates a complex influence of secondary and tertiary alteration
processes on the present-day material properties. The simulated models are constrained to reproduce
observed rock property values at the locations of actual samples (subject to discretization limits). Else-
where, the simulated property values vary stochastically within the statistical bounds of the measured data.
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Rautman, C.A. & McKenna, S.A. Three-dimensional hydrological and thermal property models of Yucca Mountain, Nevada, report, November 1, 1997; Albuquerque, New Mexico. (digital.library.unt.edu/ark:/67531/metadc689852/m1/4/: accessed April 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.