Flooding Induced Effects from the Mining Lake Goitzsche on Groundwater and Land‐use in the Bitterfeld Area

Abstract

The exceptional flooding event of the river Mulde in August 2002 led to an unexpected filling of the Goitzsche, an open‐pit lignite mining lake, within two days. Due to this exceptional situation, the groundwater table in the vicinity of the lake rose several meters in the area of Bitterfeld. Over the last 100 years, this region has been affected by a large‐scale contaminated aquifer of the former chemical industry complex Bitterfeld/Wolfen. Consequent to the rising groundwater level, the regional hydraulic situation and the groundwater flow direction changed entirely, as proven by hydraulic modelling results. Due to the heterogeneous aquifer conditions, the hydraulic importance was shown of a small scale channel‐fill at the bottom of the upper aquifer. This predominant geological structure evidently affects the groundwater flow direction indicated by the modelled path lines. The resulting pathways of the contaminants can be used for the identification of exposure routes related to areas of high ecological sensitivity. The monitoring of highly soluble groundwater contaminants (e.g. benzene, TCE, cis‐1,2‐DCE), close to the flooding event, shows (irregular patterns of increasing, as well as decreasing, concentration values of related groundwater contaminants. Until the present, no consistent regional pattern can be recorded in the shift of the distribution of the concentration induced by the flooding event. Local differences in the concentration values are obviously more related to small scale variations within the Quaternary aquifer in terms of hydraulic conductivity and higher residual concentration of the contaminated matrix sediments. The temporal effects of concentration values ca be traced back, by most of the organic compounds, to distinct observation wells within the monitored time span at the starting point before flooding.

Pit lakes of the Central German lignite mining district: Creation, morphometry and water quality aspects

“…Organic contamination of groundwater in the neighbourhood of Lake Goitsche did not affect the lake water quality due to changes in flow direction of the groundwater as a result of the flood event in 2002 (Wycisk et al, 2005). Contaminants leaving a waste deposit at the southern margin of Lake Hufeisensee via groundwater are accumulated in the monimolimnion of the lake and the respective sediment (Stottmeister et al, 1999).…”

Dioxin- and POP-contaminated sites—contemporary and future relevance and challenges

“…Another paper in the series will describe the comprehensive groundwater modelling approach developed for Bitterfeld. This is one of the largest contaminated megasites in Germany with a complex hydrological regime and which has been impacted by releases of industrial chemical and by open-pit lignite mining (Wycisk et al 2005). This process-orientated approach will be presented in this series with a focus on HCH contamination and can be regarded as a potential standard tool to facilitate decision making of remediation strategies for contaminated megasites in respect to ground water contamination.…”

Flood effects on phosphorus immobilisation in a river water filled pit lake—Case study Lake Goitsche (Germany)

“…The increase in Cl À concentrations in the pore water and in the monimolimnion above the sediment (Tables 2 and 3) suggest a stronger inflow of groundwater in August 2003. This stronger inflow of groundwater in August 2003 is probably a part of the general changes in the groundwater flow regime in the vicinity of Lake Goitsche after the flood, which was described in detail by Wycisk et al (2005) for the area north of Lake Goitsche. The Cl À concentrations in the pore water and in the monimolimnion at site N3 in August 2003 agreed well with each other and were in line with the Cl À concentrations of the groundwater at the western edge of subbasin Niemegk (3.75-6.79 mmol/L; Trettin et al, 2007), indicating inflow of water from the aquifer below the excavated lignite from western direction.…”