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Borehole DGR-3 and DGR-4 Porewater Investigations

Hobbs, M.
Koroleva, M.
Mazurek, M.
Mäder, U.
Meier, D.
Publication Geofirma Engineering Ltd, 2011
Collection DGR Site Characterization Document; TR-08-40
Description 255 p.
Abstract Intera Engineering has been contracted by the Nuclear Waste Management Organization on behalf of Ontario Power Generation (OPG) to implement the Geoscientific Site Characterization Plan (GSCP) for the Bruce site located on Lake Huron, Ontario. The GSCP is described by Intera Engineering Ltd. (Intera, 2006; 2008a). The purpose of the site characterization work is to assess the suitability of the Bruce site to construct a Deep Geologic Repository (DGR) to store low-level and intermediate-level radioactive waste. This Technical Report (TR) presents the results of porewaters investigations conducted on formations sampled in boreholes DGR-3 and DGR-4. These results are integrated with porewater characterization work conducted on DGR-2 samples (Koroleva et al., 2009), building on the understanding obtained from this earlier research. The work described in this report was completed by the Rock-Water Interaction Group, University of Bern, Switzerland, under contract to Intera Engineering Ltd. In low porosity and permeability formations in the Palaeozoic sedimentary sequence at the Bruce site, direct sampling of porewaters is not feasible. Investigating the chemical composition of porewaters requires application of a suite of indirect techniques, each of which provides partial information. The understanding of porewater composition gained from the application of these techniques can be augmented with geochemical modelling. To determine the isotopic composition of the porewaters, the diffusive exchange technique originally developed and applied by Rubel et al. (2002) has been adapted by RWI over the course of DGR site characterization activities for application to formations containing highly saline porewaters. This method was initially developed for rocks containing pore water with salinities up to seawater. Significant developments were required to adapt the method to high salinity pore waters (e.g. Waber et al., 2007; de Haller et al., 2008; Koroleva et al., 2009). The most recent and complete adaptation of this method was applied to samples from DGR-4. To obtain information on the chemical compositions of the porewaters, results of aqueous extractions were evaluated together with mineralogical and petrophysical data to assess whether the extracted ions are predominantly from porewater or significantly influenced by water-rock reactions during the extractions. Where applicable, apparent porewater compositions were derived. As part of research on samples from DGR-3, ethanol-water extractions were also investigated as a potential technique for extracting porewater while minimizing mineral-water interactions during the extraction. The results of initial testing including extractions on pure mineral phases and on DGR-3 samples are presented in this report. Out-diffusion experiments have been performed on select formations, providing information on the pore diffusion coefficients for Cl-. Estimates of apparent Cl- porewater concentrations from these experiments are compared to those determined for aliquots of the same samples using aqueous extraction. The advective displacement technique (e.g. Mäder et al., 2004; Mäder, 2005) was also tested as a direct method for the extraction of porewater from a sample of the Cobourg Formation; the results to date are summarized in this report. In the final section of the report, the status of our understanding of the chemical and isotopic composition of porewaters is evaluated and an approach for reconstructing porewater compositions using geochemical equilibrium modelling is presented.
Keywords PorewaterHydrochemistryWater isotopesMineralogyPhysical propertiesAqueous extractionOut-diffusionAdvective displacement isotope diffusive exchange.
Note Geofirma Engineering Project 08-200
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HOBBS, M. et al. Borehole DGR-3 and DGR-4 Porewater Investigations. 2011

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Deposited on : 2018-01-03

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