Study on validation method of regional groundwater flow model; Case study for Boso peninsula

Sakai, Ryutaro; Munakata, Masahiro ; Kimura, Hideo; Ichikawa, Yasuo*; Nakamura, Masaru*

In the safety assessment for a geological disposal of radioactive waste, it is important to establish modelling methods and validation methods for regional groundwater flow system in the depth of 3001000m to estimate radionuclide migration to human environment through groundwater flow system. The study discussed application of data and assessment methods for model validation based on multiple indicators such as hydrology, groundwater chemistry, temperature and age of groundwater in case of the Boso Peninsula in Chiba Prefecture where a lot of in-situ data about groundwater was measured. This results show that existing hydrochemical and thermal data are applicable to explain freshwater and saltwater distribution and groundwater flow pattern in case of regional scale. It also indicates that gravitational groundwater is likely to flow into the deep part of fresh-saltwater interface based on the exist of Na-HCO type water above fresh-saltwater interface mixed with meteoric water and that multiple indicators are applicable to evaluate groundwater flow property and groundwater flow boundary in case of site scale region.