Effects of Paleo Climate Boundary Conditions on ...

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XVI International Conference on Computational Methods in Water Resources (CMWR-XVI) Ingeniørhuset

Effects of Paleo Climate Boundary Conditions on Regional Groundwater Flow in Discretely Fractured Crystalline Rock
Author:Stefano D. Normani <sdnorman@uwaterloo.ca> (University of Waterloo)
Jon F. Sykes <sykesj@uwaterloo.ca> (University of Waterloo)
Edward A. Sudicky <sudicky@uwaterloo.ca> (University of Waterloo)
Presenter:Stefano D. Normani <sdnorman@uwaterloo.ca> (University of Waterloo)
Date: 2006-06-18     Track: General Sessions     Session: General

A detailed groundwater flow analysis for a 100 sq. km. portion of a larger regional 5734 sq. km. watershed situated on the Canadian Shield has been conducted to illustrate aspects of regional and sub-regional groundwater flow evolution due to glaciation and deglaciation events over a period of 120,000 years. Field investigations at the Underground Research Lab (URL) of the Whiteshell Research Area (WRA) near Lac du Bonnet, Manitoba, show evidence of anomalously high piezometric heads, likely resulting from surface loading from the Laurentide Ice Sheet, and high total dissolved solids (TDS) concentrations of 50 to 100 g/L in the deeper sparsely fractured rock (SFR). Consequently, long-term climate change is an important factor which can influence the safety and performance of a hypothetical used nuclear fuel repository, particularly the occurrence of peri-glacial and glacial conditions that would alter a repository’s mechanical, thermal, and hydraulic boundary conditions over a period of tens to hundreds of thousands of years. A 121,000 year continental scale paleo climate simulation is used as the basis for assigning boundary conditions and permeability reduction due to the presence of permafrost to the sub-regional scale model. Ice thicknesses of over 3,000 m and permafrost depths of more than 400 m are encountered during the course of the simulation. The discrete-fracture dual continuum finite element model FRAC3DVS was used to investigate the importance of glaciation events on flow and particle migration. Orthogonal fracture faces (between adjacent finite element blocks) were used to best represent the irregular discrete-fracture network. Crystalline rock between these structural discontinuities was assigned properties characteristic of the URL representing either SFR or moderately fractured rock (MFR). The transmissivity and porosity of the complex planar fracture zones was represented using random permeability, thickness and porosity fields that were scaled to various permeability depth models which were conditioned using data from the URL. The permeability and porosity distributions of MFR were developed in an independent inverse modeling study of tracer experiments in the MFR at the URL. Interconnectivity of permeable fracture features is an important pathway for the relatively rapid migration of average water particles and subsequent reduction in residence times.