“…However, unless the groundwater can be successfully dated, or secondary minerals observed, it is not yet possible to resolve the interaction of time and availability. In other geologic settings U concentrations may decrease with residence time, e.g., Brasser et al (2002) studied U migration in argillaceous sediments in Heselbach Site, Germany and concluded that U concentrations in groundwater decreased with flow direction due to Uretention by sorption processes.…”