Case Study: Inflow of Groundwater into Open-Cast Mine Hambach, Germany

In November 1997 an outflow of up to 0.4m3/s of groundwater from deep seated aquifers occurred in the open-cast lignite mine of Hambach, Germany. Although this incident was technically under control and did not affect the mining activities, it was studied in a joint research project to exclude recurrences at other locations. In this paper we summarize the results from a hydromechanical point of view. One key issue of this paper is to present a continuous and consistent explanation of the progression of the incident based on an analysis of the available geological, hydraulic, and chemical data. The probability of similar incidents is highly unlikely due to the rare combination of a thin sealing clay smear in the fault, high pressure gradient, and fractured coal seams in direct contact with the sealing clay. As a perspective, strategies for a responsible mining policy are derived based on the outcome of this study to prevent a recurrence of this type of incident and to ensure optimal safety for the mining operations with minimum effects on water resources.