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5. ASSUMPTIONS
The assumptions documented below are necessary to develop the Calibrated Properties Model.
This section presents the rationale for the assumptions, and references the section of this AMR in
which an assumption is used. Other assumptions basic to the Unsaturated Zone Flow and
Transport Model (UZ Model) of Yucca Mountain are elements of the conceptual model, which is
summarized at the beginning of Section 6 and will be fully documented in a future AMR
supporting the Unsaturated Zone Flow and Transport PMR, so they will not be documented in this
section.
The following assumptions are used to develop the Calibrated Properties Model.
1. It is assumed that one-dimensional (1-D) vertical flow adequately describes the flow
patterns around the boreholes used for rock mass (nonfault) property calibration
(Sections 6.1 and 6.2).
Inverse modeling involves many forward simulations, and therefore is computationally intensive.
1-D, columnar models are used because the time that is required for each forward simulation is
short (a minute or less). Therefore many simulations, thousands in this case, can be accomplished
in a reasonable (i.e., less than a day) time period. The effect of using 1-D columnar models is that
all flow is forced to be vertical; there is no lateral flow. From the surface to the repository, lateral
flow is not expected to be significant because perched water has not been found here. Below the
repository, in the Calico Hills nonwelded unit (CHn: see Table 5) and the Crater Flat
undifferentiated unit (CFu), areas of perched water exist where lateral flow may be significant.
Properties needed to produce perched water and varying degrees of lateral flow are not addressed
in this AMR but will be addressed in a future AMR supporting the Unsaturated Zone Flow and
Transport PMR. This future AMR will also address the suitability of other CHn and CFu
properties with respect to flow changes as a result of perched water and lateral flow.
2. It is assumed that 2-D flow (vertical and east-west) adequately describes the flow
patterns around borehole USW UZ-7a used for fault property calibration (Section 6.3).
As above, inverse modeling is computationally intensive. For this reason, it is necessary to use the
simplest model that will adequately simulate the system being modeled. For flow in and around a
fault zone, a 2-D model is necessary to capture the interaction of the hanging wall, fault zone, and
foot wall. An east-west, vertical cross section through USW UZ-7a and the Ghost Dance fault
should capture this interaction. The cross section is aligned approximately parallel to the dip of
the beds and parallel to the dip of the fault (perpendicular to the strike). Any lateral flow in or
around the fault zone should follow the dip of the beds and the fault.
3. It is assumed that layers bf3 and bf2 are analogs for tr3 and tr2, respectively.
No data except geologic contacts exist for layers tr3 or tr2 (the Tram Tuff). Because the Tram Tuff
has a structure similar to the Bullfrog Tuff and the two Tuffs are divided into model layers
similarly (see Table 5), the hydrologic properties should also be similar. Further, model layers tr3
and tr2 constitute only a small portion of the unsaturated zone in the northern part of the modelMDL-NBS-HS-000003 REVOO
U0035
Title: Calibrated P l
23
March 2000
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Ahlers, C. & Liu, H. Calibrated Properties Model, report, March 12, 2000; Las Vegas, Nevada. (https://digital.library.unt.edu/ark:/67531/metadc787768/m1/23/: accessed May 7, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.