Numerical simulations of possible effects of groundwater pumping on saltwater upconing in the state of Brandenburg, Germany

A. Voss, M.. Koch, Department of Geohydraulics and Engineering Hydrology, University of Kassel, Kurt-Wolters-Strasse 3, D-34109 Kassel, Germany,

A. Grewin, Landesumweltamt Brandenburg, Abt. Gewässerschutz und Wasserwirtschaft; Referat W4, Berliner Strasse 21-25, 14467 Potsdam, Germany

Saltwater intrusion from saline formation waters into groundwater extraction wells has been of concern for some time in the shallow lowlands of the state of Brandenburg, Germany. The present and future demands for increased groundwater use in the wake of recent demographic changes in the vicinity of the new German capital Berlin has significantly accentuated this problem. As new groundwater pump wellfield are being planned to satisfy the future demands, the need for proper pumping management strategies to prevent saltwater intrusion has become imminent. Numerical modeling that may have to include effects of density-dependent (DD) transport provides a powerful tool for that purpose. However, since many of the commonly used DD-codes still lack in versatility as compared with more sophisticated classical flow and transport models, a trade-off choice has to been made by the modeler to forego basic physics for better geological representation.

Based on the geological situation and the present-day chemical composition of the groundwaters in a particular region where a wellfield is being planned, we simulate, using several 2D and 3D flow and transport models, with and without density effects included, the migration of saline groundwaters. This, in order understand their origins, namely, if they are (1) derived from a major leaching saltdome in the study area or (2) are just ancient regional formation water. We find that, due to the shallowness of the aquifer system, the surficial topography has a large effect on the flow and migration patterns and, especially, gives rises to upwelling flow underneath the discharge area of the NUTE river. Comparing models, with and without density effects included, we then investigate possible saltwater upconing due this natural discharge flow pattern. Eventually the accentuated effects of the newly proposed wellfield on the upconing process is simulated, using both classical non-DD and DD- models. Based on these results, the final objective of the investigation is to provide the water agencies with a proper management plan to secure the long-term quality of the extracted groundwater.