Chemical investigations of aquifers affected by pyrite oxidation in the Bitterfeld lignite district

In a large area around the former open-pit lignite mines near Bitterfeld, G ermany, groundwater taken from wells was analyzed for the major cations, an ions, and trace elements. Quaternary and Tertiary sediments were collected from aquifers exposed on the sides of the pits and from boreholes outside t he mines and analyzed for major and trace elements, as well as for carbonat e, pyritic sulfur and total organic carbon. The pH and electrical conductiv ity of the sediments in suspension were measured. Significant differences w ere determined between the Tertiary sediments of the aquifers that were exp osed to atmospheric oxygen during the lowering of the groundwater table and those outside the cone of depression. The greatest differences were found in the pyrite content, the pH values, and the electrical conductivity, In o rder to map the degree to which the mining of the lignite has affected the quality of the groundwater in the study area, the water samples were divide d into six classes on the basis of their sulfate content. The neutralizatio n potential was calculated to estimate the potential for acidification. Pre diction of future groundwater quality is based on both (i) the present comp osition of the groundwater, surface water, and Quaternary and Tertiary aqui fer sediments and (ii) the present and future groundwater flow directions. These studies have shown which parameters are important for future groundwa ter monitoring. (C) 2001 Elsevier Science Ltd. All rights reserved.