(1) Objectives

Based on the goals set for the entire MIU Project and its Phases, the objectives of hydrochemical investigations are set as follows⁷⁾:
Data acquisition on hydrochemical properties of groundwater in the individual geological formations and geological units (fault, fracture zone, etc.) between the ground surface and the depth in the Shobasama site
Clarification of evolution mechanism of groundwater chemistry, construction of hydrochemical model and verification of its validity by examining the data
Prediction of change in hydrochemical properties of groundwater with the advance of the shaft excavation
Development of methodologies for systematic investigations and analyses of hydrohemical properties of groundwater

(2) Ways to forward the study

It is important for hydrochemical investigations to know whether the data on hydrochemical properties of groundwater obtained by investigations in the Shobasama site represent the groundwater widely distributed there. That necessitates specifying the evolution of groundwater chemistry (reaction between water and rock) by investigating geological structures, and chemical and mineralogical compositions of rocks. Furthermore, it requires the knowledge on time of reaction between rock and water. Consequently, it becomes important to know the retention time of groundwater. In addition, it is thought that the retention time of groundwater could be supporting data of the results of groundwater flow simulation⁷¹⁾. Besides, examinations of the evolution of groundwater chemistry and the retention time necessitate hydrochemical data on rain water and river water as initial conditions.