Abstract
Several hydrogeological investigation techniques have been used at the Mizunami Underground Research Laboratory site to assess hydrogeological structures and their control on groundwater flow. For example, the properties of water-conducting features (WCFs) can be determined using high-resolution electrical conductivity measurements of fluids, and compared to measurements using conventional logging techniques. Connectivity of WCFs can be estimated from transmissivity changes over time, calculated from the pressure derivative of hydraulic pressure data obtained from hydraulic testing results. Hydraulic diffusivity, obtained from hydraulic interference testing by considering the flow dimension, could be a key indicator of the connectivity of WCFs between boreholes. A conceptual hydrogeological model of several hundred square meters to several square kilometers, bounded by flow barrier structures, has been developed from pressure response plots, based on interference hydraulic testing. The applicability of several methods for developing conceptual hydrogeological models has been confirmed on the basis of the hydrogeological investigation techniques mentioned above.
