Three-dimensional inverse modeling of two large-scale cross-hole hydraulic tests in fractured granite at the Mizunami Underground Research Laboratory site, Japan

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

Two cross-hole tests were conducted at separate locations in deep boreholes at the MIU construction site in central Japan. We analyze the two cross-hole hydraulic tests using the Transient Hydraulic Tomography (THT) code of Zhu and Yeh [2005] to compute the hydraulic conductivity (K) and specific storage (Ss) distributions as well as their uncertainties in three-dimensions. The equivalent K and Ss were obtained using the asymptotic analysis served as the initial parameter estimates for the 3D stochastic inverse modeling effort. Results show 2 distinct high K and low Ss zones that are continuous over distances ranging from 550 - 1,200 m, which delineate 2 separate fault zones. The fault zones that are imaged through THT correlate well with available geological data and drawdown records. The analysis of the tests with the THT code also identified a low K zone which corresponds with a known fault zone trending NNW and has been found to compartmentalize groundwater flow at the site.