Redox potential of deep groundwater in the Horonobe area, Hokkaido, was measured, and uncertainty of the measurement and thermodynamic interpretation was evaluated. The redox potential of groundwater obtained using monitoring units in the Underground Research Laboratory ranged between －250 and －100 mV, and the effect of the excavation of drifts on the redox potential is considered to be small in spite of its temporal variation. The redox potential is controlled by the reaction of chemical pairs of SO42－/FeS2, SO42－/HS－ and CO2(aq)/CH4(aq). The comparison between the equilibrium potential for these reactions and the measured redox potentials suggests that ±50 mV of uncertainty for the measurement of the redox potential is appropriate.
This study aims to develop a new method that enables quantitative estimation of groundwater-surface water interaction by combining multiple environmental tracer analyses and geostatistics. The study area selected is around the Kamo and Takano Rivers in the Kyoto Basin, west Japan. Ordinary kriging (OK) of the analytical results of groundwater and river water samples revealed that groundwater in the aquifer near the river bed has lower chloride ion concentration and lighter oxygen isotope ratio compared to the surrounding groundwater. The domain in which the river water infiltrates could be detected by OK. In addition, groundwater inflow rate to the rivers were estimated based on radon concentration. The maximum groundwater inflow rate (36.5 m3/m/day) was obtained around the confluence of the Kamo and Takano Rivers. Mixing ratios of the groundwater in the river water were estimated as 14 % and 35 % in the Kamo and Takano River sides, respectively around the confluence.
The follow-up investigation of impacts of Tsunami caused by 2011off the Pacific coast of Tohoku Earthquake on groundwater and its usage in Asahi-city, Chiba, Japan has been conducted.
High electric conductivities (Max. 16,008μS/cm) found in well waters 2 month after the Tsunami have decreased below 1000 μS/cm in all wells in the research area by February 2018. The groundwater turn over times estimated based on the EC decrease curves obtained from wells in the area were ranged between 2.4 to 4.6 years. Yellow coloured groundwater has started to show after 2 years of Tsunami, which prevents residents from drinking well waters. 32 out of 37 residents who started to drink well water after the Tsunami ceased to drink well water again due to the colour. Based on resident hearing survey, people strongly wish to use well water for drinking again and they feel lack of information on groundwater chemistry and its perspectives. In order to prevent/decrease damage of well water from future Tsunami, perfect water proof sealing of well rids, removal of sea water/evaporation residue on the ground surface after the Tsunami, and continuing pumping up of well water were recommended.