HR: 15:45h
AN: IA33A-08    [Abstracts]
TI: Paleoclimate Impact on a Proposed Canadian Deep Geologic Repository for Low and Intermediate Level Radioactive Waste
AU: * Normani, S D
EM: sdnorman@uwaterloo.ca
AF: University of Waterloo, Dept. of Civil and Environmental Engineering 200 University Ave. W., Waterloo, ON N2L 3G1, Canada
AU: Sykes, J F
EM: sykesj@uwaterloo.ca
AF: University of Waterloo, Dept. of Civil and Environmental Engineering 200 University Ave. W., Waterloo, ON N2L 3G1, Canada
AU: Yin, Y
EM: y2yin@engmail.uwaterloo.ca
AF: University of Waterloo, Dept. of Civil and Environmental Engineering 200 University Ave. W., Waterloo, ON N2L 3G1, Canada
AB: A Deep Geologic Repository (DGR) for low and intermediate level radioactive waste has been proposed by Ontario Power Generation (OPG) for the Bruce site near Tiverton, Ontario Canada. As envisioned, the DGR is to be constructed at a depth of about 680 m below ground surface within the argillaceous Ordovician limestone of the Cobourg Formation. Within the geologic setting of southern Ontario, the Bruce site is located west of the Algonquin Arch within the Bruce Megablock, positioned along the eastern edge of the Michigan Basin. It is clear that to credibly address the long-term safety of a deep geologic repository, long-term climate change and in particular a glaciation scenario, must be incorporated into performance assessment modelling activities. In addition, by simulating flow system responses to the last Laurentide (North American) glacial episode, insight is gained into the role of significant past stresses (mechanical, thermal and hydrological) on determining the nature of present flow system conditions, and by extension, the likely impact of similar, future boundary condition changes on long-term flow system stability. The last Laurentide glacial episode was characterized by the following: occurred over a 120 000 year time period; included numerous cycles of glacial advance and retreat, with maximum ice thickness over a typical Ontario site reaching nearly 3 km; included extensive periods of transient, peri-glacial conditions during which permafrost could impact the subsurface, depending on location, to several hundreds of metres; and was accompanied by significant basal meltwater production near the end of the glacial episode. The impact of glaciation and deglaciation on density-dependent groundwater flow was investigated using results from the deterministic University of Toronto Glacial Systems Model (GSM) of continental ice-sheet evolution. The 18,500 km2 regional-scale domain extends from Lake Huron to Georgian Bay and includes 31 sedimentary strata that may be present above the Precambrian crystalline basement rock. The effects of long- term climate change on the groundwater flow system are investigated by modifying the permeability of rock within the permafrost zone, by changing the surface boundary conditions to reflect a glacial scenario, and depending on the one-dimensional loading efficiency, by the inclusion of a pressure modifying term in the flow equation. At the DGR site, two glaciation events were predicted to occur over the regional-scale domain with the first event spanning a period from approximately -62.5 kyr to -56 kyr and the most recent event occurring in the period from approximately -24 kyr to -13 kyr. Permafrost occurred approximately 12 kyr to 14 kyr prior to the onset of glaciation and was fully absent approximately 1 kyr after onset. The model results indicate that basal meltwater does not penetrate below the units of the Salina at the DGR site. The most significant consequence of glacial loading is the generation of elevated transient pore pressures throughout the rock column, with the level dependent on the compressibility of the rock and the one-dimensional loading efficiency. The analyses clearly show that glacial impact is very sensitive to local scale lithology and stratigraphy.
DE: 0720 Glaciers
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
DE: 1847 Modeling
SC: International Association of Hydrogeologists, Canadian National Chapter [IA]
MN: 2009 Joint Assembly