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    Session convener-recommended article JpGU Meeting 2013

    201412201412

    Distribution of U and REE on colloids in granitic groundwater and quality-controlled sampling at the Mizunami Underground Research Laboratory

    Munemoto T, Ohmori K, Iwatsuki T

    Mizunami Underground Research Laboratory, Colloid-facilitated transport, Quality-controlled sampling, Deep granitic groundwater, Rare earth elements, Uranium

    Description of the MIU construction site.

    (a) Schematic representation of the MIU facilities and sampling sites.

    (b) Groundwater sampling apparatus (photograph taken at the 10MI26 borehole).

    (c) Groundwater seepage from an excavated gallery wall.

    (d) Schematic representation of groundwater sampling from a borehole.

    Colloids and their association with analogue elements, uranium, and rare earth elements (REEs), in deep granitic groundwater were investigated at the Mizunami Underground Research Laboratory (MIU). Groundwater was sampled from underground boreholes and gallery walls, and the colloids were separated by size-fractionated ultrafiltration (pore sizes, 0.2 μm, 10 kDa, and 1 kDa). For the groundwater sampled from fractures in excavation walls, the size-fractionated concentrations of the colloid-forming elements were approximately constant relative to different size fractions (0.2 μm, 200 kDa, 50 kDa, and 10 kDa). The contamination of Fe- and Al-bearing materials was insignificant in the filtered groundwater from fracture seepages. Changes in the concentrations of U in the groundwater sampled from boreholes and excavation walls were associated with the Al-bearing colloids, Fe-bearing colloids, and organic matter. The REE-bearing material(s) that were >0.2 μm in size were mobile in the deep granitic groundwater, rather than occurring in association with Al-bearing, Fe-bearing colloids, and organic matter. It is suggested that sampling from water-conducting fractures in host rock and colloid elimination in borehole are important components of water quality control in geochemical investigations.