Prof. Dr Takeshi Hayashi has over 30 years of research experience in various surface and subsurface water environments in Japan and other countries and has been working on regional groundwater flow and solute transport systems integrating hydrogeological, hydraulic, geochemical properties, and age indicators. In recent years, he also has been developing a multi-tracer method using anthropogenic chemical compounds such as PPCPs and artificial sweeteners, and microorganisms in order to evaluate the groundwater flow and mass transport in urban areas.