Hydraulic tomography in fractured granite; The Mizunami Underground Research Site, Japan

Illman, W. A.*; Liu, X.*; Takeuchi, Shinji; Yeh, T.-C. J.*; Ando, Kenichi*; Saegusa, Hiromitsu

Two large-scale cross-hole pumping tests were conducted at separate locations in deep boreholes at the Mizunami Underground Research Laboratory (MIU) construction site in central Japan. We analyze the two cross-hole tests using the transient hydraulic tomography (THT) code to compute the hydraulic conductivity () and specific storage () tomograms, as well as their uncertainties in three-dimensions. The equivalent and obtained using asymptotic analysis served as the initial parameter estimates for the 3D stochastic inverse modeling effort. Results show several, distinct high and low zones that are continuous over hundreds of meters, which appear to delineate fault zones and their connectivity. The THT analysis of the tests also identified a low zone which corresponds with a known fault zone trending NNW and has been found to compartmentalize groundwater flow at the site. These results corroborate well with several hydrogeological phenomena around the site.