The coal mining goes, the water stays. The consequences for eternity and how to cope with them

The coal mining goes, the water stays. The consequences for eternity and how to cope with them

Another facet of water management in the Ruhr region is coming to the fore these days with the end of hard coal mining. Many consequences of mining are visible for miles around – even if the air and rivers are clean again, the mining damage remains. The Ruhr area is riddled with holes. On average, it has subsided by twelve meters. In addition, there are depressions up to 25 meters deep. In which the rain no longer runs off. If the water were not pumped out, a huge lake landscape would soon be created here. One example is the Phoenix Lake in Dortmund.

The deeper the Ruhr coal mining industry dug into the earth, the more water had to be pumped out. Only in this way was it possible to mine the coal at all. Because what seeps into the ground there, especially through precipitation, migrates through the cavities and fissures created by mining operations. For a long time, the areas where mining still took place were threatened. As at the Prosper-Haniel mine in Bottrop in 1.200 meters below the surface, where coal was mined until these days. To keep water away from underground mining areas, the mining industry has developed a sophisticated system known as dewatering. RAG’s work continues even after the closure of the last mine in Bottrop. Especially in the case of water drainage, the company will be faced with important tasks in the long term, the so-called "eternity tasks", also known as "eternity burdens". They are used to regulate the water balance in the region both underground and above ground.

The coal mining goes, the water stays. The consequences for eternity and how to cope with them

Mine water drainage – preventing drinking water from mixing with mine water

In order to keep shafts and roadways dry deep underground and thus to be able to extract coal at all, penetrating water had to be permanently pumped to the surface. The water was "lifted" and directed into the adjacent streams and rivers. Special attention is paid to drinking water, the mixing of which with the mine water is to be prevented. If RAG stops mining coal in the Ruhr region after 2018, there will no longer be any need to keep underground operating areas dry. This opens up opportunities to design mine water management for the long term with a focus on relieving pressure on the receiving waters. In the long term, RAG’s mine water concept envisages a reduction in the number of water retention sites, conversion to well water retention and an increase in the pumping level. For example, the average pumping height in the Ruhr region is to be raised from 900 to 600 meters. The water may rise to a maximum of 150 meters below the important drinking water reservoirs of the Haltern sands.

The advantages of future mine water drainage are obvious: the shorter the path through the rock strata, the lower the salt content; in addition, as the pumping height decreases, so does the energy consumption. Finally, numerous rivers and streams can be relieved of mine water in terms of volume. At 13 sites, around 85 million cubic meters of mine water a year are pumped up through risers in this way. This would eliminate the need to discharge mine water with salts, sediments and possible pollutants into public waters. This should not only improve the quality of the water, but also the living conditions of plants and animals on and in the watercourse.

The coal mining goes, the water stays. The consequences for eternity and how to cope with them

Groundwater management – protecting groundwater from mining pollutants

In the years when the pot was boiling, "environmental protection" was still a foreign word. On many former industrial sites, the pollutants were discharged superficially and thus got into the soil. The consequences were impurities that contaminated the soil. Especially from the end of the 19. until the middle of the 20. At the beginning of the twentieth century and as a result of destruction during the Second World War, pollutants such as tar and aromatic hydrocarbons were released, particularly from coking plants and ancillary extraction facilities. In many cases it was too late to protect the soil, but the groundwater was in danger. The pollutants sink further and further into the ground through the rain and endanger the groundwater. This must also be prevented in the future.

The groundwater is therefore monitored as part of the "perpetual pollution" program. Groundwater monitoring at almost 100 sites from Ahlen in the east to Kamp-Lintfort in the west is providing around 2.100 measuring points provide data on the quality of the groundwater. The analysis results show if there is contamination of the groundwater, if groundwater purification is necessary or if remediation success is apparent. The contaminated water is then pumped to a connected purification plant. This filters out the pollutants with activated carbon. The water is only discharged into the sewage system if it meets the official discharge standards. More than 20 rehabilitation and pumping plants with over 80 production wells or. Drainages are currently in operation. In the coming years, more groundwater purification plants may be added at several locations. Around 680.000 cubic meters of groundwater are cleaned by RAG in this way each year.

Polder measures – Where the Ruhr region and Holland are similar

The last of the three areas of RAG’s "eternal tasks" are the polder measures. Anyone coming to the Ruhr for the first time will be surprised to see crooked front doors or wide cracks in building facades. Those who live here are familiar with the "subsidences", hardly any region has been spared. Nature is also affected, so streams can no longer flow down a free gradient. The depressions – so-called polder areas, which are actually only known in Holland – have to be artificially drained to prevent surface water from collecting in them. As a result, more than one billion cubic meters of water per year are pumped throughout the Ruhr region – equivalent to the amount of water that flows through the Rhine near Duisburg in five days.

The Emschergenossenschaft explains its important role in balancing the water flows in the Ruhr region as follows: "Shift in the shaft" is the motto for coal mining in the region – but not for the pumping stations on the Emscher and Lippe rivers. The Emschergenossenschaft, which was founded in 1899 and plays a special role as a special-law association and operates many wastewater facilities, started operating the first pumping station on the Alte Emscher in Duisburg in 1914 to regulate the water balance. The Emschergenossenschaft and Lippeverband water management associations, which have now merged organizationally, have the eternal task of keeping the area from "drowning": 344 pumping stations drain the so-called polder areas, some of which have sunk by up to 25 meters as a result of coal mining. They account for almost 40 percent of the region’s groundwater.

A classic example is the stream that would have to flow "backwards" or floods depressions because its gradient has changed. Waterlogging can also occur, as is known from peatlands. They occur when the distance between the surface and the groundwater level decreases and the water cannot flow away. In short, to ensure that the Ruhr region does not sink in the long term, pumps must be operated to regulate the groundwater level as part of the "eternity tasks". Pumps ensure that the water flows in its original direction, even at the deepest point of a body of water. The challenge explained Dr. Emanuel Grun, technical director of Emschergenossenschaft and Lippeverband: "The facilities should and should be capable of raising the runoff that occurs, even during the heaviest precipitation events. If they were shut down, large parts of our region would be under water".

The coal mining goes, the water stays. The consequences for eternity and how to cope with them

Environmental protection – planned mine water management also has opponents

"Where there is light, there must also be shadow", the change in mine water management does not only find supporters. For decades, mining was the "sacred cow". Protected because of its industrial and employment significance. For a long time, environmental and nature conservation associations have had to watch helplessly as mining has wreaked havoc on the land and the waters. This has cost a lot of trust. It is therefore not surprising that the environmental associations now have doubts as to whether the "burdens of eternity" will actually be borne by RAG after the end of mining and whether everything will really be taken into account. Environmental association BUND NRW is concerned about the quality of public waters and in the course of this criticizes the approval procedures, because as is well known, mining is subject to mining law and this is something very special for the reasons mentioned at the beginning of this article. But water law also has to be observed, and this sets strict standards. BUND stands by its criticism. Nevertheless "This mine water rise", says BUND, "The mine water management project currently being applied for and implemented by RAG represents the biggest environmental problem for the entire water management and hydrogeology of the Emscher Lippe Ruhr region. Despite an increase in mine water to a level that is compatible with water management, large quantities of mine water will have to be discharged into surface waters in the long term. This mine water is heavily contaminated with chlorides, heavy metals and other pollutants. In addition, the large quantities of PCBs, which were used underground in the past, are released into the environment via the mine water." BUND NRW is therefore calling for greater transparency and that "a final operating plan procedure and a planning approval procedure under mining law with an environmental impact assessment must be carried out."

It will certainly be necessary to advance scientific knowledge in the prevention and treatment of mine water and groundwater management. To this end, RAG has an extensive concept entitled "Concept for the long-term optimization of RAG’s mine water drainage for NRW". This is based on a so-called legacy contract from the year 2007. Accordingly, a whole series of conditions must be observed when implementing the water conservation concept. This also includes the question of economic viability, i.e., the question of costs. The mine water concept for North Rhine-Westphalia presented by RAG AG was discussed in a specially formed "mining safety subcommittee" of the North Rhine-Westphalia state parliament and accepted as future-proof (see sources).

Research and dialogue – the task of the "Mining and Water Forum" foundation

It is important to identify and research the challenges and incorporate new findings into appropriate mine water concepts. To this end, RAG has donated five million euros to promote science and research in this field. This research is to drive forward the five-year foundation "Forum Mining and Water. The forum, in which renowned scientists participate, is administered in trust by the Stifterverband fur die Deutsche Wissenschaft e.V. (see sources). The tasks of the forum include, for example, the "conception of monitoring measures for mine water rise processes". In this way, the precautionary principle is taken into account, and at the same time the Forum also sees itself as a mediator between research and the interests of citizens and the environment, and seeks dialog with those affected by it. With the aim of presenting initial research projects and generating impetus for further research, the Forum held its first dialog event on the topic of "Mine Water: Developing Sustainable Solutions" in Bochum a year ago. Things will get exciting on 7. February 2019. Then a second dialog event will take place in Saarbrucken. The agenda is still being worked on, explained to me on request, Rainer Ludtke, Head of Science Foundations German Foundation Center, representing the Forum. In any case, a lively discussion is expected.

Heat turnaround – residential buildings heated with mine water

The nexus "mine water and energy" shows where the journey in research can go. We know warm sources and their importance as CO2-free heating energy. Standing in front of a geyser in Iceland gives you a feel for it. This is also possible with mine water. Warm mine water from coal mines and opencast lignite mines can make a noticeable contribution to heating homes in North Rhine-Westphalia, according to calculations from a study just published by the NRW State Environment Agency (LANUV). For example, in the regions of hard coal mining alone, warm mine water, which can be used via water retention sites or accessible shafts, could provide a heat quantity of around 1.300 gigawatt hours per year are made available in the reference year 2035 for the future heat supply in NRW. This corresponds to the heat demand of approx. 75.000 single-family households. If one takes the warm mine water alone from the mining regions studied in NRW, a saving of up to 1.2 million tons of CO2 per year should be possible. A particularly high technical potential is offered especially by the remaining water retention sites of the hard coal mining industry, since here the potential could be taken to a very large extent by surrounding heat sinks in the immediate vicinity of the "warm springs". This example shows that the conversion of the mining industry not only poses challenges and possible risks, but also has potential for environmental protection. Heat is referred to as the "sleeping giant of the energy transition".

Today is the last day of mining

Mining goes, infrastructure stays. The challenges will also be preserved for future generations. The protection of the environment and the waters has a different emphasis today than when mining began. Society has become more sensitive, laws stricter. It is mining and the industrial development based on it that have given us, with all their facets, those CO2 emissions and ecological consequences that must be subsumed under the term climate change. We will have to work on the challenges as a society. Water supply is one of them, as has been demonstrated in this 2018 summer – the warmest since weather records began. No matter how the next summer turns out, RAG will stay with us so that the eternal tasks and their burdens do not fall into the "mining free zone.

Good luck!

Note: This series of articles on "Energy and water" will be continued. After this prelude "Hard coal phase-out", the next article will deal with lignite and water – see here "What are the consequences of the lignite phase-out in Lusatia for the water industry??" (Guest article by Dr. Uwe Grunewald) from 23.2.2021

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