Detection of iron-rich groundwater "hot spots" entering streams in Lusatia

In the German Lusatian Lignite Mining Region, high iron concentrations occur in the groundwater, which discharges to natural streams and brings about unfavourable conditions. It was suspected that the iron load to streams varies greatly in space, and that the contamination originates from discrete point sources (hot spots). Water quality analyses of the few local monitoring wells were found to be insufficient to characterise the problem. A direct push technique for exploring iron hot spots was therefore developed to better identify the areas of high priority for remediation. The developed method was tested at a 700-m-long section of the stream "Kleine Spree", where the presence of hot spots was expected and the planning of remedial measures is already underway. Along that section several samples have been taken from the stream bank and a large spatial variation of iron concentrations was found. While the highest detected dissolved iron concentration in the groundwater beneath the stream bank was about 400 mg/L, 50 m downstream the concentration was only about 240 mg/L and 100 m further it decreased to 50 mg/L. Temperature measurements were conducted to qualitatively characterize the groundwater influxes along the studied section of the stream.