Safe yield of deep groundwater aquifers - a case study from mineral water production

Deep groundwater aquifers offer a high-quality drinking water supply and serve as a vital reserve in emergencies because no prior treatment is required. However, considering its slow replenishment, deep groundwater in its original hydrochemical composition, and age structure has to be considered as a finite resource. At the same time its extraction alters both the hydraulic and hydrochemical dynamics of the aquifer. Ensuring the long-term availability and protection of mineral water necessitates sustainable management practices to prevent depletion of the reservoir or "mineral water mining".

This study aims to develop concepts determining the sustainable yield of mineral water, using time-series of the hydrochemical signature and persistent organic trace substances. Together with production data this concept elucidates the flow paths in the deeper aquifer and the availability of the mineral water resource. The different approaches are discussed and illustrated using a deep groundwater aquifer that has been used for bottled water production since the early 1900s. Following the stop of the production in 2020 we observed a rather rapid increase of the hydraulic potential and a slower decrease of persistant trace chemicals. The concentration of dissolves solids recovered faster for the deeper wells compared to the more shallow wells. The hydrochemical signature reveals a change in the ion ratios which can be attributed to changing mixing ratios in the groundwater wells.

The unique data collected before and after the shut-down of the operation suggests that the mineral water, in its original composition has been depleted in the shallow parts of the stratified fracture aquifer. The concepts developed in this study would have suggested a lower limit to the extraction rates and volumes to sustain the operation.