Results of remediation of hard coal overburden and tailing dumps after a few decades: Insights and conclusions

The historical hard coal mining area of the districts of Zwickau and Lugau/Oelsnitz in Saxony (Germany) is a source of heavy metals and arsenic polluting the adjacent ground- and surface waters. Some of the dumps are partially older than 150 years, and some of them were remediated more than 50 years ago. Today we still can learn from the more or less successful remediation measures after some decades of application. In this paper, three different dumps are presented and differences between their remediation measures and long-term success are pointed out. As a result, especially a sealing and covering of a dump turned out as very successful for the prevention of AMD (acid mine drainage) generation. Thus, a reduction of the specific seepage water load of SO42−, Zn2+, Ni2+ and Cd2+ up to 85%, 98.6%, 98.5% and 99.98%, respectively, compared to a revegetated, but not additionally covered dump could be achieved. The covered dump has been stable since more than 50 years; only a low pyrite oxidation grade was detected. But also the infiltration of oxygen consuming organic substance from the top of the dumps and/or by inflowing groundwaters makes a further contribution to the long-term stabilization of a former coal mining dump by keeping the redox potential of such a material quiet low. Microbial investigations resulted in increased counts of sulfate reducers depending especially on the availability of infiltrating organic substance. T. denitrificans seems to be abundant in a moderately acidic environment with nitrate infiltration and atmospheric input. her utilization of such a remediated and revegetated area is possible, or it can be “given back” to the nature. By contrast, only revegetation without covering of a dump results in a long-term AMD generation of such a mining site.