Modelling the Long-term Release of Sulphate from Dump Sediments of an Abandoned Open Pit Lignite Mine
The generation of acid drainage from overburden spoil piles at open-pit lignite mines impacts water quality in large parts of the Lusatian mining area in Germany. The Lohsa Mine was exploited until the early 1990s and is to be flooded by 2005. It will then be used as a reservoir basin for the river Spree. Future acidity and sulphate concentrations in the surface water are of great interest because considerable amounts of the bank filtrate of the river are used to supply drinking water to communal water plants downstream. In our study, the input of sulphate from the unsaturated zone of the heap into the groundwater was calculated using the one dimensional reactive transport code SAPY. The SAPY program, which had been calibrated for effective diffusion and tortuosity using oxygen breakthrough curves of a column experiment with original heap sediments, was scaled up to field conditions and verified by measuring the oxygen and sulphate profile of the heap. Scenarios for a period of 80 years were simulated for different distances of the groundwater level to the subsurface, and the mass input of sulphate from the unsaturated zone into the groundwater was calculated in terms of specific fluxes for different times. Plans are to use the calculated source terms in a regional three-dimensional model to predict the evolution of the ground- and surface water in the area.