HR: 15:15h
AN: IA33A-06    [Abstracts]
TI: Diffusion Measurements in Low-Permeability Ordovician Sedimentary Rocks From Southern Ontario
AU: * Al, T A
EM: tal@unb.ca
AF: Department of Geology, University of New Brunswick, P.O. Box 4400, Fredericton, NB E3B 5A3, Canada
AU: Xiang, Y
AF: Department of Geology, University of New Brunswick, P.O. Box 4400, Fredericton, NB E3B 5A3, Canada
AU: Cavé, L
AF: Department of Geology, University of New Brunswick, P.O. Box 4400, Fredericton, NB E3B 5A3, Canada
AU: Loomer, D
AF: Department of Geology, University of New Brunswick, P.O. Box 4400, Fredericton, NB E3B 5A3, Canada
AU: Vilks, P
AF: Atomic Energy of Canada Limited, Whiteshell Laboratories, Pinawa, MN , Canada
AU: Van Loon, L
AF: Paul Scherrer Institut, 5234, Villigen PSI, Switzerland
AB: Effective diffusion coefficients for tritiated water (HTO) and iodide tracers, defined as: D_e = φ δ D₀ / τ² where: D_e = solute-specific effective diffusion coefficient (m²s^-1); D₀ = solute-specific free-water diffusion coefficient (m²s^-1); φ = diffusion accessible porosity (-); τ = tortuosity (- ), and δ = constrictivity (-) were measured for samples of Ordovician sedimentary rocks from southern Ontario using through-diffusion (TD) and X-ray radiography techniques. Water-loss porosities were also measured using a gravimetric technique that involves drying to 105 ^oC. The work was conducted as part of on-going investigations related to Ontario Power Generation's proposed DGR at the Bruce site, near Tiverton, Ontario. The radiography method was used effectively for samples with porosity > 0.03 (3%) and TD was used for the low-porosity limestone. In a comparison exercise, diffusion measurements on paired samples using the radiography and TD methods provide consistent results. In addition, results from diffusion measurements conducted independently in three different labs compare favourably. The water-loss porosity values for the Ordovician shales range from 0.053 to 0.10 (5.3 to 10%), and the water-loss porosities from the Ordovician limestones range from 0.005 to 0.021 (0.5 to 2.1%). The D_e values for iodide tracer in shale samples from the Bruce site range from 4.1 x 10^-13 to 6.3 x 10^-12 m²/s, and values for iodide tracer in limestone samples from the Bruce site range from 7.8 x 10^-14 to 1.2 x 10^-12. D_e values for HTO tracer in shale samples from the Bruce site range from 4.3 x 10^{- 13} to 4.8 x 10^-12, and values for HTO tracer in limestone samples from the Bruce site range from 1.0 x 10^-13 to 2.3 x 10^-12. With increasing depth, there is a general trend to lower D_e values from the top of the Ordovician shales (approximately 450 mbgs) to the top of the Ordovician limestones (approximately 650 mbgs), with no trend evident in D_e values from the limestones. Anisotropy was investigated with paired sub-samples, oriented parallel and normal to bedding. For iodide tracer, the D_e values parallel to bedding are 0.4 to 5.5 times larger (mean = 2.2) than those obtained normal to bedding. For HTO tracer, the D_e values parallel to bedding are 1.3 to 8.2 times larger (mean = 3.2) than those obtained normal to bedding. Values of D_e obtained with HTO are up to 2.5 times greater than D_e values obtained with iodide.
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
DE: 5114 Permeability and porosity
DE: 5139 Transport properties
SC: International Association of Hydrogeologists, Canadian National Chapter [IA]
MN: 2009 Joint Assembly