Million-year-old groundwater revealed by krypton-81 dating in Guanzhong Basin, China

Groundwater age, defined as the mean subsurface residence time spent isolated from the atmosphere, is of crucial significance for managing water resources and industrial waste. It is also very useful for understanding subsurface contaminant transport, and for paleoclimate reconstruction. It is an important parameter for characterizing aquifer hydrogeology including aquifer storage capacity, the rate of groundwater renewal, and flow velocity.