After 150 years of industrial mining, large areas in Middle Germany are affected by miming related activities that deeply impact the hydro-geology of the region, change the groundwater regime by intensive pumping and leave large pit lakes behind. Remediation measures for abandoned mines coexist with active mining in close vicinity.
Two regional scale groundwater models based on the modeling system PCGEOFIM are used to quantify these impacts and the effectiveness of remediation. They cover areas of several thousand square kilometers. Each model includes about 80 lakes and numerous rivers as coupled boundary conditions. In addition local modeling using boundary conditions from the regional models is performed to investigate more detailed processes, such as water quality, at finer spatial resolution.
Detailed modeling was carried out for Lake Zwenkau to the south of Leipzig, an open pit lake that will be filled with about 180 million m3 of water in the next few years. The water quality of the forming lake is of great importance, because the lake is intended to be used for recreational purposes where there is considerable acid mine drainage (AMD) from the surrounding dumps. The groundwater model was coupled with the lake model CE-QUAL-W2, a quasi three-dimensional model for lake hydrodynamics, transport, and biological water quality, which in turn was coupled with PHREEQC to account for very low pH-values induced by AMD. Predictions of future water quality were made to enable planning of adequate measures to establish a suitable water quality.