Depletion of a Mineral Water Aquifer – Implications on Sustainable Groundwater Management

Deep groundwater extraction alters both the reservoir's hydraulic and hydrochemical state. Although deep groundwater is part of the hydrologic cycle, it is considered a limited resource regarding the original hydrochemical composition and age structure. Mineral water producers share the privilege to use this resource for commercial purposes. Here, geological protection against surface influences and highly constant hydrochemical conditions are legally required.

This study evaluates the development of a deep groundwater aquifer that has been used for bottled water production since the 1900s. Production stopped in late 2019, offering the unique opportunity to study the recovery of the aquifer. Detailed data from the past 40 years show a hydrochemical stratification in the mineral water aquifer with salinity and age increasing with depth. The saltwater horizon seems to have been lowered significantly due to extraction, and the hydraulic potential has also decreased. A connection to shallow groundwater was confirmed through the detection of herbicide metabolites. Isotope activities and metabolite concentrations indicate that the travel times are between 5-10 years.

After the shutdown of the operation, the hydraulic potential increased and some of the wells are now again artesian. In the first analyses of the hydrochemical conditions the deepest wells reveal increasing salinity and CO₂ concentrations. This indicates that the saltwater horizon is now moving upwards. The shallower wells, however, still show slightly decreasing salinity and are far away from the original hydrochemical composition. This indicates that the water extraction at this site has to be considered a mining operation.

The measurements of the hydraulic and hydrochemical development together with an investigation of the flow paths for the recharge will allow an assessment of the sustainability of the groundwater extraction at this and other sites.