Final Outcome of Sulfate Transport Modelling and a Prediction of Ground and Surface Water Quality in Aquifers Influenced by Lignite Mining in Germany

摘要

Lignite mining in central Germany has played an important role for more than 100 years. Former and present mining activities, as well as remediation processes, affect the aquifers. The investigation area, south of the city Leipzig, occupies 205 km~2. For this area, the environmental objectives of the European Union (EU)'s Water Framework Directive are currently not achieved. A prediction of ground and surface water qualities has been established focussing on pyritic sulfuroxidation and the generation of sulfate .To predict the sulfate migration out of overburden dumps into unaffected aquifers, as well as the influence on surface waters, several steps were necessary. The first step involved characterization of the un-disturbed overburden material to predict the geochemical behaviour of the dumps. Therefore, a geological model, generated from several thousand drillings, was formed. Furthermore the concentrations of sulfur and carbonate, within the different geological layers, were examined in the geochemical model. The average dump compositions were based on a blending of the geochemical parameters with the thickness of the different geological layers.The prediction of dump water quality was carried out using PhreeqC (Parkhust & Apello, 1999) modelling. Predicted amounts of weathering products were used to calculate the equilibrium between groundwater, secondary minerals (gypsum, siderite) and CO2 concentration of the gas phase by consideration of redox reactions, mineral dissolution, precipitation and cationic exchange. The flow and one component transport modelling for the investigation area was carried out by the existing large scale model (HGMS) of the company IBGW Leipzig and was based on the flow and transport code PCGEOFIM?. Selected "Hotspot zones" were subsequently modelled using a reactive hydro-geochemical transport model, based on the program code PHT3D.The results describe an expansion of dump water plumes into unaffected aquifers within the stratigraphic sequence from the upper to the lower layers.