Development and Application of a Database of Deep Groundwater Chemistry using Geographical Information System (GIS)

From the viewpoint of geological disposal of high-level radioactive waste, it is necessary to understand a wide range of geological environments such as physical and chemical characteristics of rock formation and groundwater therein. We have collected more than 1000 of groundwater samples in all over Japan, and developed a database of deep groundwater chemistry. The database contains information on geographical location, sampling depth, pH, Eh, water temperature, conductivity, concentrations of major anion and cation, and stable isotope ratios (e.g. 2H, 13C, 18O). To evaluate geochemical characteristics of groundwater in Japan, the data were plotted onto a geological information system (GIS), and classified into major rock-type categories (i.e. sedimentary rock, accretionary complex, volcanic rock, plutonic rock, and metamorphic rock) according to a digital geological map. The sedimentary rock and accretionary complex were further divided into their ages (e.g. quaternary and neogene), whereas the volcanic rock and plutonic rock were divided into detailed rock types (e.g. silicic and mafic). We report the preliminary results of the hydrochemical feature of groundwater in various rock types using piper diagrams, and discuss its usefulness. This research project has been conducted under the research contract with the Nuclear and Industrial Safety Agency (NISA).