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Title: Influence of faults on groundwater flow and transport at YuccaMountain, Nevada

Abstract

Numerical simulations of groundwater flow at Yucca Mountain, Nevada are used to investigate how faults influence groundwater flow pathways and regional-scale macrodispersion. The 3-D model has a unique grid block discretization that facilitates the accurate representation of the complex geologic structure present in faulted formations. Each hydrogeologic layer is discretized into a single layer of irregular and dipping grid blocks, and faults are discretized such that they are laterally continuous and varied in displacement varies along strike. In addition, the presence of altered fault zones is explicitly modeled, as appropriate. Simulations show that upward head gradients can be readily explained by the geometry of hydrogeologic layers, the variability of layer permeabilities, and the presence of permeable fault zones or faults with displacement only, not necessarily by upwelling from a deep aquifer. Large-scale macrodispersion results from the vertical and lateral diversion of flow near the contact of high- and low-permeability layers at faults, and from upward flow within high-permeability fault zones. Conversely, large-scale channeling can occur as a result of groundwater flow into areas with minimal fault displacement. Contaminants originating at the water table can flow in a direction significantly different from that of the water table gradient, and isolated zonesmore » of contaminants can occur at the water table downgradient. By conducting both 2-D and 3-D simulations, we show that the 2-D cross-sectional models traditionally used to examine flow in faulted formations may not be appropriate. In addition, the influence of a particular type of fault cannot be generalized; depending on the location where contaminants enter the saturated zone, faults may either enhance or inhibit vertical dispersion.« less

Authors:
;
Publication Date:
Research Org.:
Ernest Orlando Lawrence Berkeley NationalLaboratory, Berkeley, CA (US)
Sponsoring Org.:
USDOE
OSTI Identifier:
926686
Report Number(s):
LBNL-44635
R&D Project: 0; BnR: YN0100000; TRN: US0803126
DOE Contract Number:  
DE-AC02-05CH11231
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
58; CHANNELING; GEOLOGIC STRUCTURES; GEOMETRY; TRANSPORT; UPWELLING; WATER TABLES; YUCCA MOUNTAIN

Citation Formats

Cohen, Andrew J.B., and Sitar, Nicholas. Influence of faults on groundwater flow and transport at YuccaMountain, Nevada. United States: N. p., 1999. Web. doi:10.2172/926686.
Cohen, Andrew J.B., & Sitar, Nicholas. Influence of faults on groundwater flow and transport at YuccaMountain, Nevada. United States. doi:10.2172/926686.
Cohen, Andrew J.B., and Sitar, Nicholas. Thu . "Influence of faults on groundwater flow and transport at YuccaMountain, Nevada". United States. doi:10.2172/926686. https://www.osti.gov/servlets/purl/926686.
@article{osti_926686,
title = {Influence of faults on groundwater flow and transport at YuccaMountain, Nevada},
author = {Cohen, Andrew J.B. and Sitar, Nicholas},
abstractNote = {Numerical simulations of groundwater flow at Yucca Mountain, Nevada are used to investigate how faults influence groundwater flow pathways and regional-scale macrodispersion. The 3-D model has a unique grid block discretization that facilitates the accurate representation of the complex geologic structure present in faulted formations. Each hydrogeologic layer is discretized into a single layer of irregular and dipping grid blocks, and faults are discretized such that they are laterally continuous and varied in displacement varies along strike. In addition, the presence of altered fault zones is explicitly modeled, as appropriate. Simulations show that upward head gradients can be readily explained by the geometry of hydrogeologic layers, the variability of layer permeabilities, and the presence of permeable fault zones or faults with displacement only, not necessarily by upwelling from a deep aquifer. Large-scale macrodispersion results from the vertical and lateral diversion of flow near the contact of high- and low-permeability layers at faults, and from upward flow within high-permeability fault zones. Conversely, large-scale channeling can occur as a result of groundwater flow into areas with minimal fault displacement. Contaminants originating at the water table can flow in a direction significantly different from that of the water table gradient, and isolated zones of contaminants can occur at the water table downgradient. By conducting both 2-D and 3-D simulations, we show that the 2-D cross-sectional models traditionally used to examine flow in faulted formations may not be appropriate. In addition, the influence of a particular type of fault cannot be generalized; depending on the location where contaminants enter the saturated zone, faults may either enhance or inhibit vertical dispersion.},
doi = {10.2172/926686},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Oct 07 00:00:00 EDT 1999},
month = {Thu Oct 07 00:00:00 EDT 1999}
}

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