1) Objectives

Based on the goals set for the entire MIU Project and its Phases, the objectives of hydrogeological investigations are set as follows⁷⁾.
Data acquisition on the geological units (faults, fractures,etc.) that could be migration paths of groundwater and on the hydraulic heterogeneity of the rock mass (lithofacies, weathering, alteration, etc.)
Construction of hydrogeological model and verification of its validity
Understanding of the groundwater hydrology in the Shobasama site and predictions of its changes and the amount of water inflow caused by shaft excavation
Development of methodologies for systematic investigations and analyses of hydro-geology

2) Ways to forward the study

It is important for forwarding the study to ascertain the following points :
the extent of understanding of the obtained information
the uncertainty of data/models
the priority of the data acquisition for decreasing the uncertainty
The study is expected to evaluate the uncertainty by implementing a "analysis loop of groundwater hydrology" (henceforth "analysis loop"; Fig.4.25). The analysis loop is set based on the approaches of investigations and analyses shown in Fig.3.1.

3) Construction of hydrogeological model

Hydrogeological models in the rock mass are classified into a continuum model that deals with the rock mass as a porous and continuous medium and a discontinuum model that takes discontinuous structures such as fractures into consideration. In the MIU Project, both continuum and discontinuum models are supposed to be adopted to examine the applicability of each modeling methodologies.

In the Phase I-a, the continuum model is adopted for following reasons.
shortage of information on the distribution of fractures and permeability
constraints of time and computation amount (It takes too long time to analyze the study area as a discontinuum).

This aims at evaluating the validity of the modeling methodologies. In this methodology, physical properties of area macroscopically divided according to the density/tendency of fracture distribution are replaced with an equivalent continuum.

4) Overview of the current status

During the Phase I-a, two analysis loops are implemented. In the 1st analysis loop, only the information obtained from the RHS Project and the study in the Tono Mine is used for construction of the hydrogeological model and the groundwater flow simulation.

In the 2^nd analysis loop, the information obtained in the MIU Project is added to the data used in the 1st loop. And the hydrogeological model is constructed and groundwater flow simulation is carried out. In this 2^nd analysis loop, problems suggested to be solved after the 1^st analysis loop are taken into consideration.

Besides, in the Shobasama site is carried out a groundwater flow simulation. The purposes are as follows.
modeling a fault that is thought to be an important geological structure controlling groundwater hydrology
understanding the effects of hydraulic boundary conditions on the results of groundwater flow simulation
The results⁴⁴⁾ of the simulation are omitted here.