Groundwater Transport Characteristics of Fracture Zones in a Granite Batholith

by C. C. Davison, AECL Research/Whiteshell Lab, Pinawa, Canada,
L. H. Frost, AECL Research/Whiteshell Lab, Pinawa, Canada,
E. T. Kozak, AECL Research/Whiteshell Lab, Pinawa, Canada,
N. W. Scheier, AECL Research/Whiteshell Lab, Pinawa, Canada,
C. D. Martin, AECL Research/Whiteshell Lab, Pinawa, Canada,

Document Type: Proceeding Paper

Part of: High Level Radioactive Waste Management 1993


Major low-dipping fracture zones are the dominant pathways for the large scale circulation of groundwater through the Lac du Bonnet granite batholith of southeast Manitoba, Canada. The groundwater transport characteristics of one of these zones have been thoroughly studied at a variety of different size scales as part of investigations done during the siting and development of a 450 m deep underground research laboratory (URL). Complex patterns of permeability can exist within these fracture zones and permeabilities can vary by as much as 6 orders of magnitude over distances of a few metres. Some regions of high permeability form interconnected networks which can be traced for distances of more than 1 km. Measurements of in-situ stress and fracture stiffness reveal that the regions of high permeability correlate to regions of very low normal stress and low fracture stiffness. Conversely, regions of low permeability within the fracture zones are regions of high normal stress and high fracture stiffness. The tracer breakthrough data from groundwater tracer tests performed in the high permeability regions of the fracture zones is best simulated by transport models that partition the transport into spatial domains of distinctly different transport properties.

Subject Headings: Permeability (soil) | Stiffening | Groundwater | Cracking | Probe instruments | Water circulation | Underground structures | Field tests | Canada | Manitoba

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