A HYDROGEOLOGICAL 3D STRUCTURE MODEL VISUALISING THE GORLEBEN SALT DOME OVERBURDEN IN NORTHERN GERMANY

The salt dome of Gorleben is situated in Northern Germany between Hamburg and Berlin near the river Elbe and has been investigated as potential repository for nuclear waste. Therefore, the salt dome overburden as well has been investigated intensively by means of an extensive drilling and exploration programme from 1979 to 1998. We now verify that data and combine them to a consistent hydrogeological 3D structure model.

First step of the modelling process has been the definition of hydrogeological units regarding the hydrogeological properties of geological units. The model bases upon 456 well logs, 10 geological cross-sections and 18 geological contour maps including subcrops. From this data 1697 model cross-sections have been constructed providing the line framework for surface calculation. We resort to a line-based modelling software (openGEO) because of complex sediment bodies especially included in the glacial and periglacial deposits of Saalian age.

The salt dome and its cap rock are covered by sediments of Tertiary and Quaternary age. The Oligocene Rupel Clay is regarded as base of the groundwater system in the overburden. Between Rupel Clay and Hamburg Clay, the Lower Lignite Sands of Miocene age have aquifer quality. In Quaternary, lower Elsterian sands are divided from highly inhomogeneous Saalian deposits by the aquitard Lauenburg Clay Complex. The most remarkable interface of the model is the Quaternary base. Lower Quaternary sediments are deposited in channels incised into Tertiary layers. Therefore, the Tertiary Hamburg Clay and the Quaternary Lauenburg Clay Complex together build up one aquitard which widely separates a narrow fresh water deposit from a deeper ground water body mainly consisting of higher concentrated brine.

The model is intended to serve as base for three-dimensional numerical modelling of hydrological parameters with special emphasis on spatial changes in groundwater density as a function of brine concentration.