Estimates of the Mean Residence Time (MRT) or age distributions of groundwater are primarily possible by tracer measurements (e.g. dye, isotope and gas-tracers, etc.) and numerical modeling (e.g. direct simulation of age). The session wants to bring together experience of applied resource management and advanced research using a wide range of different techniques to estimate groundwater age-distributions in variable aquifers. Knowing the residence time or groundwater ages can be important for
1) surface-groundwater interaction and protecting groundwater dependent eco-systems,
2) to estimate the vulnerability and the recovery-time of groundwater bodies impacted by pollution,
3) to define drinking water protection areas and planning the sustainable use of water resources,
4) to quantify quality problems due to climate change impacts, 5) to evaluate numerical groundwater models etc.