Présentations Colloques

Oral Presentation
Session 8.10: Recent developments in groundwater modeling and mathematical tools in Hydrogeology
Aus Der Beek Martina
Longterm Saltwater injection into a confined aquifer- A density-coupled mass-transport model taken to the max?
In the vicinity of a potash mine, highly saline production waters have been injected into a con-fined, deep carbonate rock aquifer for over 90 years. This carbonate rock aquifer is a regional aquifer with naturally occurring, extensive salinity variations of its formation waters. Alternating duration, location, and timing, 62 wells were used to inject highly saline production waters. **The aim of the project was, based on available data and results of geological works and mining investigations, to develop a numerical groundwater model capable of simulating the impact of the injection regime of the past 90 years on regional flow patterns and solute transport under-ground, and identifying possible relations between saltwater injections and non-point saltwater inflows into the nearby river. **The model has thus been taken to its limits with regards to three aspects- 1) simulation of density dependent flow of highly dense waters and strong gradients of salinity+ 2) a simulation length of 90 years for past and current conditions complemented by additional 45 years of scenario simulation time+ and 3) the aquifer itself as well as the large overburden are included in the 3D modelling space to give a holistic picture of the total groundwater flow behaviour in the region for an area of 1220kmC with a maximum depth of 1000m. Modelling was carried out with the three-dimensional density-coupled flow and mass-transport simulation system FEFLOWy.**This contribution will discuss obstacles and challenges involved in the whole modelling process, from model set-up over actual simulation, verification and interpretation of results. Owing to the large 3D modelling space and the long simulation period, the clash of scales of measured field data (point measurements) and expected regional interpretation of flow behaviour became particularly obvious. Specifically in the light of public perception and political decision making, two almost opposing requirements of representing locally anthropogenic and natural impacts and characteristics while interpreting regional flow pattern and density-dependent system behaviour had to be overcome.