One of the important methods for the safety assessment of the geological disposal of HLW (high-level radioactive waste) is a performance assessment based on a numerical model of groundwater flow. Thus, improvement of groundwater flow model is crucial for the reliability of the safety assessment. To improve the groundwater flow model, it is useful to use the groundwater monitoring data for its validation and updating. For this purpose, water level, pore pressure and chemical composition of groundwater in wells are often monitored, while systematic geophysical monitoring is not widely used. In this paper, we reviewed the case studies of the geophysical exploration method used for the groundwater monitoring and proposed its feasibility to the monitoring program for geological disposal of HLW especially for gravity, resistivity, self potential, and micro-seismicity. Monitoring of these data should be started from early stage of the site selection survey for capturing the baseline characteristics before the groundwater perturbation caused by construction of the shafts and drifts. With these monitoring data, computer codes called "post-processor" is often used to calculate geophysical parameters using groundwater flow model for the parameter matching. It is emphasized that progress of modeling technology including the development and validation of these codes is important as well as the progress of monitoring technology.
