Hydrogeological investigations of surface-based investigation phase of Horonobe URL project

Kurikami, Hiroshi  ; Takeuchi, Ryuji  ; Yabuuchi, Satoshi; Seno, Shoji*; Tomura, Goji; Shibano, Kazunori; Hara, Minoru; Kunimaru, Takanori

Japan Atomic Energy Agency has been conducting the Horonobe Underground Research Laboratory (URL) project in Horonobe, Hokkaido, as a part of the research and development program on geological disposal of high-level radioactive waste. This paper shows the results of hydrogeological investigations in the surface-based investigation phase of the project. Hydrological and meteorological investigations show that the infiltration rates of the drainage basins varies and that the infiltration rate depends on the flora and the topography. The hydraulic tests using the deep boreholes reveals that hydraulic conductivity of the scale of a few decameters to a hundred meter varies widely and decreases with depth in the same formation, while the laboratory hydraulic tests suggest that hydraulic conductivity of the intact rock is influenced by the stress history. The hydraulic tests and the long-term monitorings of hydraulic pressure clarify relatively high pressure in the deep underground. Furthermore, groundwater flow analysis shows that the groundwater in and around the URL area flows regionally from the east to the west and depends locally on the geography and geology.