Ninth International Conference on Permafrost ... - IARC Research

Deep Permafrost Studies at the Lupin Mine:Hydrogeological and Geochemical Information for Nuclear Waste DisposalLasse AhonenGeological Survey of FinlandTimo RuskeeniemiGeological Survey of FinlandRandy StotlerUniversity of Waterloo, CanadaShaun FrapeUniversity of Waterloo, CanadaKimmo LehtoPosiva Oy, FinlandIgnasi PuigdomenechSKB (Swedish Nuclear Fuel and Waste Management Co), SwedenMonique HobbsNuclear Waste Management Organization, CanadaPaul DegnanNirex, UK (present position CSIRO Exploration & Mining, Australia)IntroductionThe deep geological disposal of high-level and long-livednuclear waste requires a comprehensive understanding ofthe possible impacts of long-term future climate change ona repository environment and the surrounding rock mass.Despite the general scientific consensus that global warmingis underway due to anthropogenic greenhouse gas emissions,future glaciation scenarios have to be taken into accountand included in the long-term safety analyses of disposalsystems, especially in Fennoscandian countries, Britain, andCanada.The Lupin gold mine, situated in the territory of Nunavut,Canada, is located in a subarctic tundra environment,where continuous permafrost reaches depths of 400–600m. The bedrock of the Lupin area consists of Archeanmetasedimentary crystalline rocks, which are consideredto be good analogues for host rocks at potential repositorysites in the Fennoscandian Shield. Consequently, severalnuclear waste management organizations, together withthe Geological Survey of Finland and the University ofWaterloo, started a joint venture to study the hydrogeologicaland hydrogeochemical conditions below and within thepermafrost at the Lupin mine (Ruskeeniemi et al. 2003).Several important uncertainties relating to the potentialeffects of permafrost on the safety of nuclear waste disposalwere identified as follows:• Depth range and rate of formation of permafrost incrystalline rock and the controlling factors.• Hydrogeological conditions in frozen rock, theimportance of taliks as possible flow paths and thefreezing of water in major fracture zones.• Hydrogeochemical effects of permafrost, formationof saline segregations (cryopegs) in and/or below thefrozen rock mass.• Methane hydrates, the abundance and formation ofmethane in crystalline rock and the nature of anyaccumulations below the permafrost.Research ActivitiesThe research project at the Lupin mine was conductedin three phases. During the first phase, background data ongeology and hydrology were compiled, potential fracturezones were identified by a seismic refraction study, andunderground waters were sampled (Ruskeeniemi et al.2002). Phase II activities included an electromagnetic survey(SAMPO), drilling of two research boreholes from insidethe mine upwards through the bottom of the permafrost,water and gas sampling, crush and leach studies of therock material, and freezing experiments of water samples(Ruskeeniemi et al. 2004, Frape et al. 2004).Phase III (Stotler et al. 2008) focused on the collectionof representative data concerning the chemistry and isotopiccomposition of waters and dissolved components frompacked-off boreholes, the long-term monitoring of hydraulicheads in the boreholes, mineralogical studies of fracturedrock, and a ground penetrating radar survey.Hydrogeological ConditionsIn the mine, the bedrock below the permafrost down toabout 900 m appeared distinctly dry, as observed along theramp roadway. Mine statistics indicate pumping rates ofabout 6 m 3 /h (in 2003), of which a major proportion wasidentified to be fresh water supplied for various purposes inthe mining process. Most of the water-producing boreholessituated at the level 1130 m were plugged. At higher levelsthe seepage of groundwater through frozen bedrock does notappear to take place at all. Measured effective porosities of1