Hydrogeological compartment structure; Significance of its identification and characterization in geological disposal program

Takeuchi, Shinji*; Saegusa, Hiromitsu; Takeuchi, Ryuji  

In hydrogeological characterization of a potential disposal site, one of the specific concerns is to understand what happens if an underground facility is constructed in a hydrogeological compartment (HC) bounded by faults within a fractured rock. If the faults have very low permeability, groundwater cannot easily flow into the HC from its surroundings, causing a huge drawdown in the HC. If the faults have moderate permeability, groundwater can easily flow into the HC, causing a large drawdown outside the HC. Changes in static pressure heads and pressures in response to earthquake have been observed within a larger block bounded by the faults and/or lineaments in the Tono area, central Japan. Because such a HC generally exists in Japan, it is crucial to identify and characterize the HC at varying spatial scales at a potential disposal site.