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Abstract: This paper presents a study of solute transport through ground water in the saturated zone and the resulting breakthrough curves (BTCs), using a field-scale numerical model that incorporates the processes of advection, dispersion, matrix diffusion in fractured volcanic formations, sorption, and colloid-facilitated transport. Such BTCs at compliance boundaries are often used as performance measures for a site. The example considered here is that of the saturated zone study prepared for the Yucca Mountain license application. The saturated zone at this site occurs partly in volcanic, fractured rock formations and partly in alluvial formations. This paper presents a description of the site and the ground water flow model, the development of the conceptual model of transport, model uncertainties, model validation, and the influence of uncertainty in input parameters on the downstream BTCs at the Yucca Mountain site. [ABSTRACT FROM AUTHOR]

This paper describes the development and use of a particle-tracking model to perform radionuclide-transport simulations in the unsaturated zone at Yucca Mountain, Nevada. The goal of the effort was to produce a computational model that can be coupled to the project''s calibrated 3D site-scale flow model so that the results of that effort could be incorporated directly into the Total System Performance Assessment (TSPA) analyses. The transport model simulates multiple species (typically 20 or more) with complex time-varying and spatially varying releases from the potential repository. Water-table rise, climate-change scenarios, and decay chains are additional features of the model. A cell-based particle-tracking method was employed that includes a dual-permeability formulation, advection, longitudinal dispersion, matrix diffusion, and colloid-facilitated transport. This paper examines the transport behavior of several key radionuclides through the unsaturated zone using the calibrated 3D unsaturated flow fields. Computational results illustrate the relative importance of fracture flow, matrix diffusion, and lateral diversion on the distribution of travel times from the simulated repository to the water table for various climatic conditions. Results also indicate rapid transport through fractures for a portion of the released mass. Further refinement of the model will address several issues, including conservatism in the transport model, the assignment of parameters in the flow and transport models, and the underlying assumptions used to support the conceptual models of flow and transport in the unsaturated zone at Yucca Mountain. [Copyright &y& Elsevier]

Experimental data have demonstrated that a strong relationship exists between the state parameter and the peak strength and dilatancy characteristics of sands. This paper proposes a way of reproducing this behaviour using a modified Mohr-Coulomb failure criterion, which retains its simplicity while improving substantially its modelling capabilities. The formulated constitutive model is calibrated for Nevada sand following a well-defined procedure and used in the prediction of four centrifuge tests investigating the behaviour of axially loaded footings. It is shown that the proposed model reproduces well both the element tests and the more complex footing problems, demonstrating its usefulness for engineering practice. Moreover, a simplified version which does not require the definition of the Critical State Line is proposed for situations when this aspect of soil behaviour cannot be determined with confidence. It is shown that such simplification results in only slightly less accurate predictions than the full version of the model, while simulating aspects of soil response that cannot be reproduced using constant values for strength and dilatancy parameters. [ABSTRACT FROM AUTHOR]

As climate change research burgeons at a remarkable pace, it is intersecting with research regarding indigenous and rural people in fascinating ways. Yet, there remains a significant gap in integrated quantitative and qualitative methods for studying rural climate change perception and policy support, especially with regard to Native Americans. The objectives of this paper are to utilize our multi-method approach of integrating surveys, interviews, video, literature and fieldwork in innovative ways to: (1) address the aforementioned gap in rural studies, while advancing knowledge regarding effective methodologies for investigation of linkages between socio-political variables and climate change perceptions; and (2) perform comparative primary research regarding the climate change assumptions, risk perceptions, policy preferences, observations and knowledge among rural Nevada's tribes and tribal environmental leaders, non-native ranchers and farmers, and America's general public. The results of this study have ramifications for similar populations in arid and semi-arid lands, particularly in the U.S. Southwest. [ABSTRACT FROM AUTHOR]

The main objectives of this study were to explore the means of reducing or eliminating snow build-up on rear warning lights and snow cloud in the wake of snowplow trucks during high-speed snowplowing (HSSP). These snow build-up on rear surfaces and snow cloud in the wake zone cause serious safety and efficiency problems due to diminishing visibility for the following motorists and amount of time needed to clear snow off from rear surfaces of snowplows. Furthermore, research and studies were carried out to solve the visibility problems experienced by the State of Nevada Department of Transportation (NDOT) snowplow trucks. Fluent 6.3.26 and ANSYS Fluent 12.1 Computational Fluid Dynamics (CFD) were utilized, and field tests were conducted with the mechanical design methods which were feasible and compatible with the snowplow trucks. Previously designed and installed rear foil (airfoil) helped reducing snow accumulation on most of the rear surface of truck except the right taillight. However, its effect in reducing snow cloud in the wake of the truck was limited. In this study several new designs were developed computationally including modifications on the current airfoil design. Based on computational (CFD) results, two of these designs were constructed and tested on NDOT trucks during routine HSSP. Preliminary test results showed promising results. Design process and test results are discussed in this paper. • 3D Computational Fluid Dynamics (CFD) snowplow truck models were utilized to study flow around and rear section of snow plow trucks. • Aerodynamic add-on device prototypes were designed and simulated using 3D CFD models. • Two aerodynamics add-on devices were designed, manufactured, and tested on an actual (full-scale) snow plow trucks during High-Speed Snowplowing (HSSP). • Field tests validated with CFD results and showed promising results. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates influence of pavement macrotexture on paved road PM10 emissions. This study was conducted on different paved roadway types (local, collector and minor arterial) in the Las Vegas Valley, Nevada. Pavement macrotexture was measured using the ASTM E 965 sand patch method and the Digital Surface Roughness Meter™ (DSRM™). A controlled constant soil loading with known PM10 fraction was applied to cleaned road surfaces. The Desert Research Institute''s (DRI) Mini-PI-SWERL™ (Portable In-Situ Wind ERosion Lab) was used to estimate PM10 mass emissions and cumulative mass emitted from pavement surfaces. PM10 mass emissions using controlled applied soil loadings generally declined with increasing pavement macrotexture at all applied shear levels. The relationships were statistically significant, and indicate that pavement macrotexture may need to be included in future development of revised paved road PM10 emissions factors. A change in the slope of emitted PM10 mass and pavement macrotexture occurred between 0.8 and 0.9 mm mean texture depth (MTD). Anomalies in PM10 mass emissions were observed at MTDs exceeding 1.2 mm. Two-way frequency distributions of pavement surface features obtained from DSRM measurements were analyzed to explain the observed anomalies. Results showed that pavement surface feature size distributions may influence on PM10 emissions from paved roads at similar MTDs. PM10 mass emissions were found to linearly depend on adjusted mode size of the pavement surface aggregate. A sharp decrease in friction velocities, computed from wind erosion theory, at MTDs above 0.9 mm matched an observed sharp decrease in PM10 emissions rates at MTDs above 0.9 mm, indicating that classical wind erosion theory could be adapted for non-erodible pavement surfaces and linearly relate PM10 emissions rates to applied shear stress at an aerodynamic roughness height of 0.075 mm. [Copyright &y& Elsevier]

Abstract: Between 1997 and 2002, 16 cases of acute childhood leukemia were diagnosed in children who either lived in Churchill County, Nevada at the time of diagnosis or had lived in the county before their diagnosis. The cases were characterized as a cluster of like illnesses and the probability of having such a cluster occur by chance was estimated to be very small (approximately one in 2.33×108). This suggested that the cluster could be linked to one or more physical, limnological, chemical, or biological agents. This review discusses the setting in which the cluster took place, the epidemiological investigations carried out by the Nevada Bureau of Health Protection Services, the National Center for Environmental Health Centers for Disease Control and Prevention and the Agency for Toxic Substances and Disease Registry, and subsequent investigations supported by a special allocation of federal funds through the US Environmental Protection Agency’s Region IX office in San Francisco, CA. This review is meant as background for the papers in this special issue that report results from multi- and interdisciplinary research into environmental and biological factors potentially related to the Churchill County leukemia cluster. [Copyright &y& Elsevier]

Abstract: Significant advances in regional groundwater flow modeling have been driven by the demand to predict regional impacts of human inferences on groundwater systems and associated environment. The wide availability of powerful computers, user friendly modeling systems and GIS stimulates an exponential growth of regional groundwater modeling. Large scale transient groundwater models have been built to analyze regional flow systems, to simulate water budget components changes, and to optimize groundwater development scenarios. This paper reviews the historical development of regional groundwater modeling. Examples of Death Valley and Great Artesian Basin transient groundwater models are introduced to show the application of large scale regional groundwater flow models. Specific methodologies for regional groundwater flow modeling are descried and special issues in regional groundwater flow modeling are discussed. [Copyright &y& Elsevier]

Abstract: Field experiments were conducted in Nellis Dunes Recreational Area (Clark County, Nevada, USA) to investigate emission of dust produced by off-road driving. Experiments were carried out with three types of vehicles: 4-wheelers (quads), dirt bikes (motorcycles) and dune buggies, on 17 soil types characteristic for a desert environment. Tests were done at various driving speeds, and emissions were measured for a large number of grain size fractions. This paper reports the results for two size fractions of emissions: PM10 (particles <10 μm) and PM60 (particles <60 μm). The latter was considered in this study to be sufficiently representative of the total suspendable fraction (TSP). Off-road driving was found to be a significant source of dust. However, the amounts varied greatly with the type of soil and the characteristics of the top layer. Models predicting emission of dust by off-road driving should thus consider a number of soil parameters and not just one key parameter. Vehicle type and driving speed are additional parameters that affect emission. In general, 4-wheelers produce more dust than dune buggies, and dune buggies, more than dirt bikes. Higher speeds also result in higher emissions. Dust emitted by off-road driving is less coarse than the parent sediment on the road surface. Off-road driving thus results in a progressive coarsening of the top layer. Exceptions to this are silty surfaces with no, or almost no, vegetation. For such surfaces no substantial differences were observed between the grain size distribution of road dust and emitted dust. Typical emission values for off-road driving on dry desert soils are: for sandy areas, 30–40 g km−1 (PM10) and 150–250 g km−1 (TSP); for silty areas, 100–200 g km−1 (PM10) and 600–2000 g km−1 (TSP); for drainages, 30–40 g km−1 (PM10) and 100–400 g km−1 (TSP); and for mixed terrain, 60–100 g km−1 (PM10) and 300–800 g km−1 (TSP). These values are for the types of vehicles tested in this study and do not refer to cars or trucks, which produce significantly more dust. [Copyright &y& Elsevier]

Abstract: We analyzed a data set of thermally induced changes in fractured rock permeability during a 4-year heating (up to 200°C) and subsequent 4-year cooling of a large volume, partially saturated and highly fractured volcanic tuff at the Yucca Mountain Drift Scale Test, Nevada, USA. Permeability estimates were derived from about 700 pneumatic (air-injection) tests, taken periodically at 44 packed-off borehole intervals during the heating and cooling cycle from November 1997 through November 2005. We analyzed air-permeability data by numerical modeling of thermally induced stress and moisture movements and their impact on air permeability within the highly fractured rock. Our analysis shows that changes in air permeability during the initial 4-year heating period, which were limited to about one order of magnitude, were caused by the combined effects of thermal-mechanically induced stress on fracture aperture and thermal-hydrologically induced changes in fracture moisture content. At the end of the subsequent 4-year cooling period, air-permeability decreases (to as low as 0.2 of initial) and increases (to as high as 1.8 of initial) were observed. By comparison to the calculated thermo-hydro-elastic model results, we identified these remaining increases or decreases in air permeability as irreversible changes in intrinsic fracture permeability, consistent with either inelastic fracture shear dilation (where permeability increased) or inelastic fracture surface-asperity shortening (where permeability decreased). In this paper, we discuss the possibility that such fracture asperity shortening and associated decrease in fracture permeability might be enhanced by dissolution of highly stressed surface asperities over years of elevated stress and temperature. [Copyright &y& Elsevier]

This paper describes total gaseous mercury (TGM) concentrations measured in Reno, Nevada from 2002 to 2005. The 3-year mean and median air Hg concentrations were 2.3 and 2.1ngm−3, respectively. Mercury concentrations exhibited seasonality, with the highest concentrations in winter, and the lowest in summer and fall. A well-defined diel pattern in TGM concentration was observed, with maximum daily concentrations observed in the morning and minimum in the afternoon. A gradual increase of TGM concentration was observed in the evening and over night. The early morning increase in TGM was likely due to activation of local surface emission sources by rising solar irradiance and air temperature. The subsequent decline and afternoon minimum in TGM were likely related to increased vertical mixing and the buildup of atmospheric oxidants during the day resulting in increased conversion to oxidized species that are quickly deposited, coupled with weakening of the surface emissions processes. The described diel pattern was seasonally modulated with the greatest amplitude in variation of TGM concentrations occurring in the summer. It is suggested based on the comparison of diel TGM pattern with other gaseous pollutants that natural source surface emissions are a dominant source of TGM in the study area. [Copyright &y& Elsevier]

Abstract: Increasing tension in the Nevada ranch community may have had a negative impact on social capital. Social capital is important because it facilitates cooperation in resolving social dilemmas related to public range management. In this paper, we use a survey of public grazing permit holders in Nevada to investigate factors that affect ranchers'' relationships with the U.S. Forest Service and Bureau of Land Management. Results indicate that, contrary to expectations, economic factors such as income and ranch size have little or no effect on relationships in the Nevada ranch community — on ranchers'' disagreements with public land managers and the deterioration in rancher-land agency relations. Rather, these relationships appear to be affected to a greater extent by our measures of social capital, personal characteristics and experience with wildfire. Indeed, disagreements with the public agencies were mainly affected by gender (males tended to have more disagreements), lack of trust, and disputes concerning responses to wildfire (which increased the chance of disagreement). Not surprisingly, disagreement resulted in a deterioration of relationships that could be offset by higher levels of social capital, particularly trust and positive attitudes towards the future of ranching and the community (as measured by responses to a variety of attitudinal questions). We conclude that, while there remain opportunities to build on existing social capital in the community (horizontal relations), ranchers and the public agencies need to work on building vertical relations, thereby increasing trust. This could potentially help in the resolution of social dilemmas related to range management. [Copyright &y& Elsevier]

Abstract: This paper presents results of five creep tests conducted in uniaxial compression at room temperature. The test specimens were from the welded Topopah Spring tuff formation at Yucca Mountain, Nevada. The specimens exhibited brittle failure. Multiple stress levels were applied in steps to each specimen. Each stress level was maintained for 3 days or longer. The transient creep for all the stress levels can be well described by power functions. The transient creep is caused by an elastic aftereffect. The tuff does not show real steady-state creep. The so-called steady-state creep rate decreases with time. In general it is very low, typically in the range of 10−7 h−1. For the first 50h, the so-called steady-state creep rate may be described as a power function of stress. The specimen failed shortly after it entered into the accelerating creep phase. [Copyright &y& Elsevier]

Abstract: This paper presents thermo-hydro-mechanical (THM) analyses simulating the Drift Scale Test (DST) performed at Yucca Mountain. A double structure approach based on two superimposed domains is adopted. Intrinsic permeability changes with deformations imply full THM coupling. Temperatures and gas permeabilities were measured during 4 years and are used to validate the model. Measured gas permeability variations show patterns that are successfully explained by the model calculations. These gas permeability variations may be attributed to thermo-hydraulic effects, and also to mechanical effects. Different cases of intrinsic permeability variations have been considered in the model and their influence on the calculated temperatures, degree of saturations and gas permeabilities are presented. Volumetric deformation, in contraction or dilatancy, implies changes in the aperture of rock fractures that in turn lead to changes in intrinsic permeability. Dilatancy, caused by shear stresses, increases intrinsic permeability. Consideration of this factor contributes significantly to improve the agreement of calculated gas permeability with the measured values obtained during the DST experiment. [Copyright &y& Elsevier]

Abstract: Xu et al. (2003) [Xu, T., Sonnenthal, E., Bodvarsson, G., 2003. A reaction-transport model for calcite precipitation and evaluation of infiltration–percolation fluxes in unsaturated fractured rock. J. Contam. Hydrol., 64, 113–127.] presented results of a reaction-transport model for calcite deposition in the unsaturated zone at Yucca Mountain, and compared the model results to measured abundances in core from a surface-based borehole. Marshall et al. (2003) [Marshall, B.D., Neymark, L.A., Peterman, Z.E., 2003. Estimation of past seepage volumes from calcite distribution in the Topopah Spring Tuff, Yucca Mountain, Nevada. J. Contam. Hydrol., 62–63, 237–247.] used the calcite distribution in the Topopah Spring Tuff to estimate past seepage into lithophysal cavities as an analog for seepage into the potential repository waste emplacement drifts at Yucca Mountain in southern Nevada (USA). Dublyansky and Smirnov (2005) [Dublyansky, Y.V., Smirnov, S.Z., 2005. Commentary: assessment of past infiltration fluxes through Yucca mountain on the basis of the secondary mineral record—is it a viable methodology? J. Contam. Hydrol. (this issue).] wrote a commentary paper to Marshall et al. (2003) [Marshall, B.D., Neymark, L.A., Peterman, Z.E., 2003. Estimation of past seepage volumes from calcite distribution in the Topopah Spring Tuff, Yucca Mountain, Nevada. J. Contam. Hydrol., 62–63, 237–247.] and Xu et al. (2003) [Xu, T., Sonnenthal, E., Bodvarsson, G., 2003. A reaction-transport model for calcite precipitation and evaluation of infiltration–percolation fluxes in unsaturated fractured rock. J. Contam. Hydrol., 64, 113–127.], containing two points: (1) questionable phenomenological model for the secondary mineral deposits and (2) inappropriate thermal boundary conditions. In this reply we address primarily the modeling approach by showing results of a sensitivity simulation regarding the effect of an elevated temperature history that approximates the temperature history inferred from fluid inclusions by Wilson et al. (2003) [Wilson, N.S.F., Cline, J.S., Amelin, Y.V., 2003. Origin, timing, and temperature of secondary calcite–silica mineral formation at Yucca Mountain, Nevada. Geochimica et Cosmochimica Acta, 67 (6), 1145–1184.]. Modeled calcite abundances using the time-varying temperature history are similar to the results for the steady-state ambient temperature profile (Xu, T., Sonnenthal, E., Bodvarsson, G., 2003. A reaction-transport model for calcite precipitation and evaluation of infiltration–percolation fluxes in unsaturated fractured rock. J. Contam. Hydrol., 64, 113–127), and are still consistent with the measured abundances at the proposed repository horizon. [Copyright &y& Elsevier]

Abstract: Two papers recently published in the Journal of Contaminant Hydrology by Marshall et al. [Marshall, B.D., Neymark, L.A., Peterman, Z.E., 2003. Estimation of past seepage volumes from calcite distribution in the Topopah Spring Tuff, Yucca Mountain, Nevada. J. Contam. Hydrol. 62–63, 237–247] and Xu et al. [Xu, T., Sonnenthal, E., Bodvarsson, G., 2003. A reaction–transport model for calcite precipitation and evaluation of infiltration fluxes in unsaturated fractured rock. J. Contam. Hydrol. 64, 113–127] attempt to assess past volumes of seepage and infiltration fluxes through the vadose zone of Yucca Mountain, Nevada, on the basis of the modeling of the spatial distribution of secondary calcite. In this commentary, we argue that the employed methodology is not viable. In addition, the thermal boundary conditions used in simulations do not correspond to the temperatures of the mineral forming fluids established on the basis of the fluid inclusion studies. [Copyright &y& Elsevier]

Abstract: The use of cosmogenic nuclide dating methods place in doubt the long-term future of weathering rinds (WRs) as a chronometric tool. Why estimate ages when radiometric control is possible? This paper presents evidence that WRs can provide invaluable clues about what particular sample would provide the most accurate cosmogenic age by avoiding “inheritance” of cosmogenic nuclides and by avoiding boulders undergoing spalling. The key to this new use requires testing the occurrence and nature of WR erosion. Back-scattered electron microscopy reveals that ignimbrite, andesite, basalt, and granitic clasts experience WR erosion in all subsurface and surface contexts thus far studied in Arizona, California, Hawaii, Oregon, and Washington. To understand the magnitude of WR erosion, we measured WR thicknesses, all while controlling the cosmogenic and surface stability ages of clasts by chlorine-36 and rock varnish microlamination dating methods. Our data reveal that traditional methodologies of sampling cobbles remove two-thirds of the true thickness of weathering rinds, calling into question many beliefs including the notion that clay minerals are not produced during weathering-rind formation. Comparisons of optical and electron microscope measurements support concerns that measurement of WRs by color changes, while useful as a pedagogical tool, creates serious biases in underestimating the true dynamics of WRs. In the end, we found that concordance of WR and rock coating “age trends” indicates the ideal boulder for cosmogenic nuclide dating. Offsets reveal either ongoing boulder erosion, invalidating “zero erosion” model ages, or a potential problem with “inheritance” of cosmogenic nuclides. [Copyright &y& Elsevier]

A weakly sorbing cation, lithium, will be used as a reactive tracer in upcoming field tracer tests in the saturated alluvium south of Yucca Mountain, Nevada. One objective of the field tests is to determine how well field-scale reactive transport can be predicted using transport parameters derived from laboratory experiments. This paper describes several laboratory lithium batch sorption and column transport experiments that were conducted using ground water and alluvium obtained from the site of the planned field tests. In the batch experiments, isotherms were determined over 2.5 orders of magnitude of lithium concentrations, corresponding to the range expected in the field tests. In addition to measuring equilibrium lithium concentrations, concentrations of other cations, namely Na+, K+, and Ca2+, were measured in the batch tests to determine Li+-exchangeable equilibria. This information was used in conjunction with alluvium cation exchange capacity measurements to parameterize a three-component cation-exchange model (EQUIL) that describes lithium sorption in the alluvium system. This model was then applied to interpret the transport behavior of lithium ion in saturated alluvium column tests conducted at three different lithium bromide injection concentrations. The concentrations were selected such that lithium ion either dominated, accounted for a little over half, or accounted for only a small fraction of the total cation equivalents in the injection solution. Although tracer breakthrough curves differed significantly under each of these conditions, with highly asymmetric responses occurring at the highest injection concentrations, the three-component cation-exchange model reproduced the observed transport behavior of lithium and the other cations in each case with a similar set of model parameters. In contrast, a linear Kd-type sorption model could only match the lithium responses at the lowest injection concentration. The three-component model will be used to interpret the field tests, with the expectation that it will help refine estimates of effective flow porosity, particularly if the lithium response curves are asymmetric. [Copyright &y& Elsevier]

This paper presents several different conceptual models of the Large Hydraulic Gradient (LHG) region north of Yucca Mountain and describes the impact of those models on groundwater flow near the potential high-level repository site. The results are based on a numerical model of site-scale saturated zone beneath Yucca Mountain. This model is used for performance assessment predictions of radionuclide transport and to guide future data collection and modeling activities. The numerical model is calibrated by matching available water level measurements using parameter estimation techniques, along with more informal comparisons of the model to hydrologic and geochemical information. The model software (hydrologic simulation code FEHM and parameter estimation software PEST) and model setup allows for efficient calibration of multiple conceptual models. Until now, the Large Hydraulic Gradient has been simulated using a low-permeability, east–west oriented feature, even though direct evidence for this feature is lacking. In addition to this model, we investigate and calibrate three additional conceptual models of the Large Hydraulic Gradient, all of which are based on a presumed zone of hydrothermal chemical alteration north of Yucca Mountain. After examining the heads and permeabilities obtained from the calibrated models, we present particle pathways from the potential repository that record differences in the predicted groundwater flow regime. The results show that Large Hydraulic Gradient can be represented with the alternate conceptual models that include the hydrothermally altered zone. The predicted pathways are mildly sensitive to the choice of the conceptual model and more sensitive to the quality of calibration in the vicinity on the repository. These differences are most likely due to different degrees of fit of model to data, and do not represent important differences in hydrologic conditions for the different conceptual models. [Copyright &y& Elsevier]

This paper presents a numerical study on the response of the unsaturated zone (UZ) system of Yucca Mountain to heat generated from decaying radioactive wastes emplaced at the proposed repository. The modeling study is based on the current thermal–hydrological (TH) mountain-scale model, which uses a locally refined 2D north–south cross-section and dual-permeability numerical approach. The model provides a prediction of the mountain-scale TH response under the thermal-load scenario of 1.45 kW/m, while accounting for future climatic changes and the effects of drift ventilation. The TH simulation results show that ventilation of the repository drifts has a large impact on thermal–hydrologic regimes and moisture-flow conditions at the repository. In both cases, with and without ventilation, the TH model predicts dry or reduced liquid saturation near the drifts for over 1000 years, during which liquid flux through the drifts is reduced to either zero or less than the ambient flux. Without ventilation, the model predicts higher temperatures at the repository, but no major moisture redistribution in the UZ except in the areas very near the heated drifts. [Copyright &y& Elsevier]

Performance assessment and design evaluation of the proposed repository at Yucca Mountain are facilitated by a thermohydrologic modeling tool that simultaneously accounts for processes occurring at a scale of a few tens of centimeters around individual waste packages and emplacement drifts, and accounts for processes at the multi-kilometer scale of the mountain. The most straightforward approach is to account for the 3-D drift- and mountain-scale dimensionality all within a single monolithic thermohydrologic model. This approach is too computationally expensive to be a viable simulation tool capable of addressing all waste-package locations in the repository. The Multiscale Thermohydrologic Model (MSTHM) is a computationally efficient alternative to addressing these modeling issues. In this paper, we describe the principal calculation stages to predict temperature, relative humidity, and liquid-saturation, as well as other thermohydrologic variables, in the drifts and in the host rock. Using a three-drift repository example (which is a scaled-down version of the proposed repository), we demonstrate the validity of the MSTHM approach against a nested monolithic thermohydrologic model. [Copyright &y& Elsevier]

This paper presents the application of parallel computing techniques to large-scale modeling of fluid flow in the unsaturated zone (UZ) at Yucca Mountain, Nevada. In this study, parallel computing techniques, as implemented into the TOUGH2 code, are applied in large-scale numerical simulations on a distributed-memory parallel computer. The modeling study has been conducted using an over-1-million-cell three-dimensional numerical model, which incorporates a wide variety of field data for the highly heterogeneous fractured formation at Yucca Mountain. The objective of this study is to analyze the impact of various surface infiltration scenarios (under current and possible future climates) on flow through the UZ system, using various hydrogeological conceptual models with refined grids. The results indicate that the 1-million-cell models produce better resolution results and reveal some flow patterns that cannot be obtained using coarse-grid modeling models. [Copyright &y& Elsevier]

A numerical model was used to simulate the flow and transport processes at the Busted Butte Field Test Site for the purpose of quantifying the effects of hydrogeologic conditions beneath the potential Yucca Mountain repository horizon. In situ experiments were conducted on a 10×10×7 m block comprising a layered Topopah Springs/Calico Hills formation with two imbedded faults. Tracer solution was continuously injected in eight parallel boreholes arranged on two horizontal planes. Twelve collection boreholes were emplaced perpendicular to the injection holes and were both horizontal and inclined. Solution samples were collected regularly using a sampling assembly consisting of an inverted membrane and sorbing-paper sampling pads. Comparisons between measurements and predictions show that, except for the occasional drops of concentrations observed in the field, the current model is able to capture the general characteristics of the system with varying levels of agreement using laboratory-measured mean hydraulic properties. Simulation results and field observations revealed a capillary-driven flow in the system. Good quantitative agreement is generally observed for near-field boreholes, however, this agreement deteriorates and the simulated solute concentration is underestimated at boreholes farther away from the injection points. Increasing the spatial resolution of the simulation improves the model predictions only to a limited extent. Scaling issues may need to be considered to describe flow and transport events, as the travel distance becomes large. [Copyright &y& Elsevier]

This paper presents CFD-DEM simulations of undrained true triaxial tests on a granular soil. A CFDEM solver that considers compressible fluid and moving meshes has been developed and calibrated against the results of laboratory testing on Nevada sand. The effect of the intermediate stress ratio (b) on the macro- and micro-mechanical features of undrained granular assemblies was studied. The tests were repeated at different confining pressures, and the trends were similar to each other. The lowest effective frictional resistance was observed for specimens for which b = 0 and the highest value was obtained for specimens with b = 0.5. An increase in b caused samples to exhibit the greatest dilative behavior and increased the absolute maximum negative excess pore pressure. The stress-force-fabric equation that represents the stress state of the assembly in terms of the fabric anisotropy and contact force anisotropy tensors was used to study the micromechanics of the undrained granular samples. The tests were varied from compression to extension in order to qualitatively and quantitatively analyze the evolution of anisotropy under anisotropic loading conditions. Observations on the microstructural evolution of undrained samples were in agreement with those already reported for drained samples. [ABSTRACT FROM AUTHOR]