3D Modeling of Saline Groundwater Flow and Transport in a Flooded Salt Mine in Stassfurt, Germany

The abandoned, flooded deep salt mine in Stassfurt, Germany has been extensively studied. The mine causes serious uncontrolled salt leaching and mass displacement effects underground that have led to significant regional-scale subsidence. Collapsing mined areas and further large-scale subsidence pose a potential danger to the city of Stassfurt. Comprehensive modeling of the three dimensional (3-D) variable density flow dynamics is required at both large and local scale to assess the stability of the cap rocks and the potential of subsidence due to salt leaching processes, and to better control (minimize) salt leaching. The impact of different engineering solutions and appropriate remedial strategies (e.g. pumping schemes) on the subsurface spatio-temporal distribution of salinity is of specific concern. Coupled variable density flow and transport simulations were performed using FEFLOW, a finite-element simulator, which is capable of both porous media (Darcy-type) flow computations and lower-dimensional discrete elements for laminar or turbulent flow. The geometry of the mine workings is incorporated in suitable detail and resolution in the developed 3-D model. Computational results were successfully compared with field observations and geophysical measurements. Different model scenarios provide better insight into flow and mass transport processes in the study area, which could provide significant information to quantify subsidence potential of the mine site.