The Influence of Open-Cast Lignite Mining on Adjacent Ground Water Systems

Abstract

Investigation area The investigated lignite mine is located Southeast of Halle (Sachsen-Anhalt, Eastern Germany), a town in the south-eastern Hartz foreland. Between 1925 and 1968 lignite was mined, first by underground mining and in later decades by open-cast mining. In the region Permo-Triassic, Tertiary and Quaternary sediments can be found. The pre-Tertiary basement shows extensive disconformities and is characterised by an intensive block structure. The hydrological situation of the area is strongly influenced by open-cast mining, because intensive water drainage was necessary to mine the local seam. The water table was lowered to the base of the mined seam by about 45 m from a natural level of 95 m above sea level. Water drainage is still performed. At least five aquifers are distinguished in the investigation area: Two river gravel aquifers occur in the Quaternary sediments. Within the Tertiary sequence several preponderantly thin aquifers are differentiated, usually limited in their lateral expansion. Locally water bearing lower Triassic sediments occur whereas a karstic aquifer in Permian dolomite and anhydrides is regionally disseminated. The ground waters in Tertiary and pre Tertiary formations are generally confined. In the surrounding of the lignite mine ground water movement in all aquifers is directed towards the pit.