The Impact of a Contaminated Lignite Seam on Groundwater Quality in the Aquifer System of the Bitterfeld Region – Modeling of Groundwater Contamination

Until 1990 the Bitterfeld region (Germany) was heavily polluted by mining, an obsolete chemical industry and the uncontrolled deposition of chemical wastes. The cessation of lignite-mining and open-pit drainage may result in a rise of the groundwater level followed by the mobilization of contaminants, especially halogenated hydrocarbons.At a research area in Bitterfeld, highly mobile chlorinated hydrocarbons were detected in both groundwater and sediments. In particular, the pollutants were found to have penetrated a lignite seam separating the quaternary and the tertiaryaquifers. The consequences of the present situation for the progressive groundwater quality of the quaternary aquifer are assessed by means of hydrodynamic modeling using the groundwater simulation program FEFLOW.Starting from the results of the preliminary investigations and adjusting the relevant hydrogeological parameters for diffusion, dispersion, adsorption and initial pollutant distributions, various scenarios were modeled and discussed. It was shown that the impact of a diffusion-controlledscenario on groundwater quality can be neglected, and that only the reversal of the advective vertical direction of flow from the lower seam border to the surface will result in a significant deterioration of groundwater quality.