How can sustainability for groundwater use be determined?

The question of sustainability contains two components: can the amount of extracted water be kept constant and will the concentration of possible contaminants remain below official limits? The understanding of water budgets and how they change in response to human activities is a key issue in this context. Although forecasts of future evolutions that are based on calibrated numerical flow models are imprecise, they nevertheless may question of sustainability is discussed for extracted groundwater (1) younger than about 50 years, (2) in the age range between about 50 years and several thousand years and (3) older than several thousand years and is illustrated in the talk by corresponding case studies. Tools are on one side direct measurements of effective or possible contaminants. On the other side chemical, physical and isotopic parameters are useful for model calibration and for the detection of trends. For instance: nitrates, salt contents, pressure heads and man made isotopes are indicators of a change of the flow system. He-3/H-3, SF6, Kr-85 and CFCs can be used for the detection of changes in the age structure, in the mixing components and in the origin and flow path of the water. Time series of these parameters and their gradients help to quantify on-going changes of the flow system and may induce restriction of groundwater extraction