A Modeling Study of Flow Diversion and Focusing in Unsaturated Fractured Rocks

Pan, Lehua; Wu, Yu‐Shu; Zhang, Keni

doi:10.2113/3.1.233

Cited by 3 publications

References 35 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

Temporal damping effect of the Yucca Mountain fractured unsaturated rock on transient infiltration pulses

Zhang

Pan

2006

Journal of Hydrology

View full text Add to dashboard Cite

Performance assessment of the Yucca Mountain unsaturated zone (UZ) as the site for an underground repository of high-level radioactive waste relies on the crucial assumption that water percolation processes in the unsaturated zone can be approximated as a steadystate condition. Justification of such an assumption is based on temporal damping effects of several geological units within the unsaturated tuff formation. In particular, the nonwelded tuff of the Painbrush Group (PTn unit) at Yucca Mountain, because of its highly porous physical properties, has been conceptualized to have a significant capacity for temporally damping transient percolation fluxes. The objective of this study is to investigate these damping effects, using a three-dimensional (3-D) mountain-scale model as well as several one-dimensional (1-D) models. The 3-D model incorporates a wide variety of the updated field data for the highly heterogeneous unsaturated formation at Yucca Mountain. The model is first run to steady state and calibrated using fieldmeasured data and then transient pulse infiltrations are applied to the model top boundary. Subsequent changes in percolation fluxes at the bottom of and within the PTn unit are examined under episodic infiltration boundary conditions. The 1-D model is used to examine the long-term response of the flow system to higher infiltration pulses, while the damping effect is also investigated through modeling tracer transport in the UZ under episodic infiltration condition. Simulation results show the existence of damping effects within the PTn unit and also indicate that the assumption of steady-state flow conditions below the PTn unit is reasonable. However, the study also finds that some fast flow paths along faults exist, causing vertical-flux quick responses at the PTn bottom to the episodic infiltration at the top boundary.

show abstract

Temporal damping effect of the Yucca Mountain fractured unsaturated rock on transient infiltration pulses

Zhang

Pan

2006

Journal of Hydrology

View full text Add to dashboard Cite

show abstract

Hydrogeologic heterogeneity of faulted and fractured Glass Mountain bedded tuffaceous sediments and ash-fall deposits: The Crucifix site near Bishop, California

et al. 2012

View full text Add to dashboard Cite

Lithologic, macrostructural, microstructural, geophysical, and in situ gas permeability data from a natural exposure of highly porous, faulted and fractured tuffaceous sediments and interbedded ash-fall deposits near Bishop, California, are presented and analyzed in relation to published geologic information. This natural analog study was motivated by the need to evaluate potential length scales over which lateral fl ow diversion might occur above and within the nonwelded Paintbrush Tuff at Yucca Mountain, Nevada. Lateral diversion of fl ow in the overlying Paintbrush Tuff was previously proposed by others as a natural barrier that might protect a proposed high-level radioactive waste and spent nuclear fuel repository from percolating water. Because the length scale for capillary barrier breakthrough and leakage is decreased in the presence of subvertical structural heterogeneities, we characterized a horst-bounding fault, small-displacement normal faults within a footwall deformation zone, and secondary heterogeneities within two beds dissected by the faults. Critical deformation-related features that may infl uence fl uid fl ow within bedded tuffaceous sediments include (1) permeability anisotropy imposed by steeply dipping faults and stratigraphic layering; (2) fault zone widths and styles, which are dependent on bed thickness and ash, glass, and clay content; and (3) fracture intensities and overprinting mechanisms (associated with fault deformation and vertical and nonvertical fracture orientations), which strongly infl uence the hydrogeologic heterogeneity of units they dissect. Microstructural analysis reveals structurally induced porosity variations at the micrometer to millimeter scale, gas permeability data show the infl uence of deformation on permeability at the centimeter to tens of centimeters scale, and resistivity and ground-penetrating radar data show lateral variations on the meter to tens of meters scale in horizontally bedded layers. All together, these observations and data show heterogeneity over seven orders of magnitude of length scale. Structurally enhanced porosity and permeability heterogeneities will tend to limit the length scale of lateral fl ow diversion, redirect fl ow downward, and enhance vertical fl uid movement within the vadose zone.

show abstract

Rare earth element transport in the Yucca Mountain region

Zhang¹

2010

View full text Add to dashboard Cite

A Modeling Study of Flow Diversion and Focusing in Unsaturated Fractured Rocks

Cited by 3 publications

References 35 publications

Temporal damping effect of the Yucca Mountain fractured unsaturated rock on transient infiltration pulses

Temporal damping effect of the Yucca Mountain fractured unsaturated rock on transient infiltration pulses

Hydrogeologic heterogeneity of faulted and fractured Glass Mountain bedded tuffaceous sediments and ash-fall deposits: The Crucifix site near Bishop, California

Rare earth element transport in the Yucca Mountain region

Contact Info

Product

Resources

About