Water Quality of Seepage in the Akaishizawa Tunnel within the Sandstone and Clay Slate Regions

Hydrogeochemical investigations were carried out for the seepage water in Akaishi tunnel which was under construction in sandstone and clay slate regions. Cations, anions, pH, electric conductivity, Eh, dissolved oxygen, tritium and oxygen isotope ratio were analysed. From the results, it was made clear that the deep groundwater is characterized by heigher pH, heigher Na+ concentration, lower Eh than the stream water. The relationship between the oxygen isotopic ratio and Eh showed that Eh can be the index of residence time of groundwater.