QuESt – Quantification of the iron sulfide turnover in the Spreewitz glacial channel (Lusatia)

Country / Region: Germany/Brandenburg/Lausatia

Begin of project: January 1, 2020

End of project: December 31, 2023

Status of project: April 13, 2022

In the past decades, the mining-related groundwater drawdown in the Lusatian lignite mining area has led to iron sulfide oxidation in the unsaturated zone and subsequently - due to the resurgence of groundwater or flooding of the open pits after mine closure - to elevated sulfate and iron concentrations in the groundwater and surface waters. In the Spreewitz glacial channel, located in the southern part of the Lusatian remediation area, iron and sulfate concentrations in groundwater are particularly high at up to 400 mg/L and 1400 mg/L, respectively. Due to the largely gaining stream conditions (groundwater seepage into the stream), this area is therefore a major source of iron and sulfate input to the Spree River. Although the processes leading to the elevated concentrations (iron sulfide oxidation and subsequent mobilization of the oxidation products) are known in principle, the distribution of iron and sulfate in the aquifers and the contribution of the different sources (natural sediments, dump and tailings deposits) are not yet fully understood. This complicates the development of a remediation concept.

The objective of the QuESt project ("Quantification of the iron sulfide turnover in the Spreewitz glacial channel") is to quantify the iron sulfide turnover in the four aquifers. In the first phase of the project, laboratory column experiments will be performed under different redox conditions on artificial sediments enriched with pyrite. The experiment will be combined with NMR (Nuclear Magnetic Resonance) to determine the correlation between iron sulfides and/or dissolved iron and the NMR signal. In a second phase (2023), NMR will be applied for a spatial characterization of the aquifers, and sediment samples will be collected at the site for comparative column studies. The mass balance calculations will be based on hydrochemical analyses as well as the accompanying laboratory NMR measurements. Continuous isotope tracer measurements will be applied for a high-precision transport characterization.

Goals/Milestones

• Determine the correlation between iron sulfides and/or dissolved iron and the NMR signal (column experiments on artificial sediments)
• Create mass balances for the iron sulfide turnover in the natural sediments of the Spreewitz glacial channel (column experiments on undisturbed samples collected from the Spreewitz channel)
• Conduct a feasibility study for the exploration of iron sulfide hotspots (surface NMR and possibly bore hole NMR)

a. Location of the Spreewitz glacial channel (green point) in the Spree catchment, and b. distribution of sulfate concentrations in the shallow aquifer of the Spreewitz glacial channel Source: Spree catchment: EU-Hydro – River Network Database, EEA (2020), sulfate concentrations: IWB (2020), groundwater contour lines: LfULG (2016)

Partner:

Lausitzer und Mitteldeutsche Bergbau-Verwaltungsgesellschaft (LMBV), Knappenstraße 1, 01968 Senftenberg (Germany)