Hydrochemical Changes Associated with Construction of Mizunami Underground Research Laboratory

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  • MIZUNO Takashi
    Tono Research Unit, Geological Isolation Research and Development Directorate, Japan Atomic Energy Agency
  • AOSAI Daisuke
    Tono Research Unit, Geological Isolation Research and Development Directorate, Japan Atomic Energy Agency
  • SHINGU Shinya
    Tono Research Unit, Geological Isolation Research and Development Directorate, Japan Atomic Energy Agency
  • HAGIWARA Hiroki
    Tono Research Unit, Geological Isolation Research and Development Directorate, Japan Atomic Energy Agency
  • YAMAMOTO Yuhei
    Tono Research Unit, Geological Isolation Research and Development Directorate, Japan Atomic Energy Agency
  • FUKUDA Akari
    Tono Research Unit, Geological Isolation Research and Development Directorate, Japan Atomic Energy Agency

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Other Title
  • 瑞浪超深地層研究所の建設に伴う地下水水質の変化
  • ミズナミ チョウシンチソウ ケンキュウジョ ノ ケンセツ ニ トモナウ チカスイ スイシツ ノ ヘンカ

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  Japan Atomic Energy Agency has undertaken the Mizunami Underground Research Laboratory (MIU) Project at Gifu Pref., central Japan. The aims of the project are to establish methodologies for investigation, analysis, and assessment of the deep geological environment, and to develop engineering techniques for deep-underground applications. The MIU consists of two vertical shafts and a number of horizontal tunnels connecting the two shafts. In this study, hydrochemical properties were monitored continuously to evaluate the hydrochemical changes during the MIU construction. The study demonstrated that groundwater salinity changed in relation to the variation of groundwater-flow conditions as a result of the shaft construction. In particular, “up-coning” of the salinity profile was observed at the bottom of the shafts owing to the upward movement of deeper groundwater. The intensity of up-coning was irregular, and depended on the hydrogeological heterogeneity of the groundwater system. Although pH rose to around 12 due to interaction with the concrete lining the shafts and with the grout injected into the adjacent host rock, it decreased to below 10 in less than 2 years. The redox condition remained reducing, which is considered to be controlled by Fe2+/Fe(OH)3(am) and/or SO4 2−/FeS2 couples. These findings can be summarized in a conceptual model.<br>

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