Global post-mining challenges Experiences gained from the German hard coal mining industry

Transcription

1 Global post-mining challenges Experiences gained from the German hard coal mining industry P Goerke-Mallet 1*, C Melchers 1 and J Kretschmann 2 1 Research Institute of Post-Mining, TFH Georg Agricola University of Applied Science, Bochum, Germany 2 TFH Georg Agricola University of Applied Science. Bochum, Germany. * Contact: Goerke-Mallet@tfh-bochum.de Abstract: Mine Closure is a global challenge. The environmental and climatic framework under which a mine closure process takes place is wide-ranging and includes various requirements. Germany s largest hard coal mining area, the Ruhr Area is the largest urban agglomeration in Germany and one of the most densely populated coal mining areas worldwide. Early coal mining activities date back to the twelfth century and since then, a total of about 10 billion tons of coal has been produced with a maximum mining depth of 1,500 m below the surface. Mining sites, deposits, specific local circumstances and consequently, the basic parameters of the mine closure process are very heterogeneous. However, there are commonalities as abandoned mine sites can affect the environment in terms of polluting the air, the burden, the water, the people and the security of the surface all over the world alike. One central task of the Post-Mining Research Institute at the University of Applied Sciences Georg Agricola in Bochum is to review best-practice cases in order to find solutions for the numerous and various problems of mine closure in Europe and worldwide. Focusing the global need for environmentally compatible closure and safekeeping methods, the primary objective should be to enhance the transparency of communication on this subject in order to transfer specific preexisting know-how across distinct mining regions all over the world. Important elements are the international exchange of experiences and the establishment of collaborations. Some of the current research projects of the Post-Mining Research Institute are: Acquisition of density stratification in flooded mine workings, Monitoring of underground flooding processes, Analysis of water-bearing adits, and the Analysis of terminated flooding processes of mines in Germany, Europe and worldwide. From our point of view the monitoring of the mine closure phase is very important. Hence, we investigate the existing possibilities concerning the survey-data of satellitebased sensors. The aim of the paper is bringing Germany s experiences from the hard coal mining industry but also from other mining branches to the global mine closure discussion in order to achieve sustainable safety for the ground surface, the population and the water bodies in combination with reasonable costs. I. INTRODUCTION In the Federal Republic of Germany the hard coal production will be phased out by the end of The abandonment of the coal mining industry triggers a crucial structural change in the former mining regions, which has to be planned and shaped actively. In order to come up with the challenges, risks and chances of post-mining, the University of Applied Sciences Georg Agricola in Bochum established a new master program for post-mining which is unique in the world. In addition, the Research Institute for Post-Mining was founded. It investigates possible solutions for central issues in coping with the perpetual obligations. A 287 major task of the Research Institute is to maintain and pass on the mining-based Know-How. The establishment of the Master course and the Research Institute is specifically promoted by the RAG-Foundation. This includes the foundation of an endowed chair. FIG 1 Mining Cycle. Mining raw materials is a finite business that reaches its limits once the deposits mined are depleted or the resources can no longer be mined in an economically profitable way. However, the impact of winning raw materials by mining is potentially an infinite one. The mining cycle can be divided into three stages: the exploration phase, the mining period and the post-mining stage (figure 1). The last phase of the mining process is probably the last one because the human interference into geology and nature is usually intensive and irreversible. Mining can lead to consequences which have a permanently adverse impact on people and the environment; therefore, they have to be managed as best as we can. In Germany, what has to be done at the post-mining stage is called Ewigkeitslasten or Ewigkeitsaufgaben which translates as perpetual obligations or perpetual tasks. The literal translation for Ewigkeit is eternity, expressing that we will have to cope with post-mining endlessly (Kretschmann, 2015). From our point of view it is necessary to focus the life cycle of a mine in all periods. As the post mining period is connected with high costs, it is reasonable to keep this period during the pre-mining stage and especially in the mining phase in mind. II. MINE CLOSURE AND POST-MINING Mining activities lead to worldwide challenges after their ending, which are often marked by similar problems. Besides a variety of risks, also numerous existing opportunities of post-mining should be exploited. In this

2 context, the Research Institute of Post-Mining at the University of Applied Sciences in Bochum works on strategies for environment friendly, sustainable and economical handling of all aspects of old- and post-mining. This includes intensive study of existing experience on the closure of mines and the risk management (Melchers et al., 2015a). The subject of mine closures is of global significance, posing a challenge for cities, regions and governments all over the world. Structural change in mining districts is a complex process comprising social, ecological, economic and cultural aspects. Therefore, the demand for environmentally compatible concepts for the back filling and plugging of mines, shafts and caverns is continuously increasing. These concepts apply to both active production plants and mines that are already closed. The handling of mine water in active mining as well as in post-mining areas yields specific challenges. Global post-mining challenges are summarize in Figure 2, which shows the main problems and effects in areas with abandoned mine sites. III. THE RUHR AREA In Germany, three coalfields are currently in the transition phase between production and closure. The largest of these is the Ruhr-area, followed by the Saarland and the coalfield around Ibbenbüren (figure 3). Production in the Saar coalfield ceased in The last remaining collieries are the Prosper-Haniel colliery in Bottrop (Ruhr-area) and the Anthrazit Ibbenbüren colliery in Ibbenbüren, which will both shut down by the end of FIG 3 - Map of Central Europe; the German coalfield regions under discussion are highlighted in black ( Worldatlasbook, edited). FIG 2 Abandoned Mining In Europe there is a strong focus on the water bodies. Directive 2000/60/EC from the European Parliament and the Council from 23 October 2000 established a framework for community action in the field of water policy. This EU water framework directive commits EU member states to achieve good qualitative and quantitative status for all water bodies by Unfortunately, in numerous cases it is still not clear how to achieve this objective. Actually there are a lot of abandoned mine sites where one can consider the problem of acid mine water. Hence the clarification of mine water is a big challenge. In this context, it should be noted that according to the court decisions of recent years and the German mining law the last mining operator is obliged to deal with the legacies and consequences resulting from all mining activities within the respected excavation site in the case of potential endangerments. The population density and the infrastructure in Germany require in all mining areas a long-term stability of the surface and a corresponding security of the people and the environment. This focus is complemented by the mentioned parameters for water and responsibility. All in all the mining companies, the mining authorities and the research institutes be under pressure to establish an efficient risk-management and best practicable environmental options (Kretschmann and Hegemann, 2012). The Ruhr-area, named after the Ruhr River, covers parts of the Federal State of North-Rhine Westphalia (NRW). The Ruhr metropolitan region covers an area of about 4,400 km2 and is populated by more than five million people living in 11 cities and four districts. It is the largest urban agglomeration in Germany and the third largest in the European Union after Paris and London. The average population-density is 1161 people per km2. In the five largest cities Duisburg, Essen, Gelsenkirchen, Bochum and Dortmund the highest population-density is 2,800 people per km² (Figure 4). The beginning of the retreat of the mining industry 50 years ago triggered a crucial structural change in the region. Today, the overall economy is dominated by service industries, high-tech operations, logistics sites and research and educational institutions. In the course of this industrialisation, the population of the Ruhr-area increased very quickly. The infrastructure of the whole region is therefore very well developed. The extraction of hard coal in the Ruhr coalfield region dates back to the twelfth century. It started in the south, where the coal seams crop out directly at the surface or underneath thin overlying quaternary sediments. The active mining site operates further in the north, where the target depth reaches up to 1,500 m. The mines in the southern part of the area were closed gradually in recent decades. In total, about 10 billion tonnes of coal have been exploited from the Ruhr deposit. The exploitable areas influence a zone of more than 3,000 km2 at the surface, and the mining-induced subsidence reaches an absolute number of 25 m locally (Melchers et al., 2015a). 288

3 16TH INTERNATIONAL CONGRESS FOR MINE SURVEYING, BRISBANE, AUSTRALIA, SEPT 2016 FIG 4 - Settlement structure of the Ruhr-area; all named cities have more than 50,000 inhabitants, and the settlement areas are marked in dark grey ( RVR, edited). IV. POST-MINING CHALLENGES The perpetual mine management obligations (also referred to as inherited liabilities with unlimited duration ) are water management measures that will continue in perpetuity even after coal mining has ceased. In order to reduce the costs for the public sector and thus for the taxpayers, RAG-Stiftung has committed itself to funding perpetual management measures for the coalfields of the Ruhr-area, Saarland and Ibbenbüren. The foundation will obtain the funds for these tasks by selling its shares in Evonik Industries AG and through income from its holdings and diversified financial assets. It should be noted that the correction of mining-related damage is not a perpetual management measure. The financing of mining-induced damage to buildings, properties and roads is and will be covered by the financial reserves of the RAG Corporation. This will also be the case after Over the centuries, mining has caused changes to landscapes. Entire regions have subsided. As a result, 30% of the morphological plane region between the rivers Emscher and Lippe is made up of polder areas potential flooding areas with no outlet (Figure 5). Diking and deepening of water bodies resulted in a hydrological system with a dominant anthropogenic character. The surface water will always have to be actively regulated in these areas in order to prevent it from collecting in the depressions. More than 200 special pumping facilities are currently operating in order to ensure that the water is properly drained. FIG 5 - Polder areas in the zone of influence of the rivers Emscher and Lippe ( EGLV, edited). To avoid flooding or pollution around and in urbanised areas, it will be necessary to maintain water management for an unforeseeable period beyond the production phase. Annually, around 70 million m3 of mine water and about 900 million m3 of ground- and rainwater in polder areas have to be pumped and drained. Beyond that, contaminated water (e.g. around former coking plants) has to be collected and cleaned to prevent it from mixing with drinking water reservoirs. The calculated annual costs for these three tasks are 220 Mill. per year and will be carried by the RAG-Foundation. As water management represents a high expense factor, thought should be given to how to reduce costs of water drainage measures by partially or completely flooding open underground mine workings. Thus, after active mining has ceased by the end of 2018, the task is to extensively flood the mine workings in the whole Ruhr-area. The rising mine water level may lead to various impacts on the caprock groundwater reservoir and on the ground surface. The protection of important drinking water reservoirs against infiltration of mine water will be a special challenge in this context. Potential risks and the level of mine water recovery have to be assessed at an early stage in the process in order to minimise these risks. In the long term, the flooding concept provides an average mine water level between 250 m below zero in the south and 600 m in the west. This will keep the mine water level far below the lowermost boundary of sub-surface groundwater horizons in order to avoid any risk of mixing. After the mine water table has reached the predicted level about 600 m below the surface, which is expected to be in 2035, it is planned to operate six main water management facilities in the Ruhr region. At these localities, well water management facilities (Brunnenwasserhaltungen) will be installed within the existing shafts (Figure 6 ). With the help of powerful submersible pumps, the water will be discharged to the surface and then pumped into the receiving watercourse. FIG 6 Schematic image of a well water management facility ( RAG Aktiengesellschaft, edited). 289

4 V. DESCRIPTION OF COMMONALITIES OF CLOSURE PROCESSES To date, Germany has been characterised by extensive abandoned surface and underground mine workings. Around 60,000 abandoned shafts and adits are expected in NRW alone, with 28,000 of these being registered at the mining authority NRW. According to the mining authority NRW, 52 % of the total land surface of NRW is affected by abandoned mining. In addition, a huge number of the presumed 60,000 openings to the surface have to be classified as not or inadequately secured. Numerous shafts and near-surface openings require longterm securing measures in order to avoid any damage to the surface and to enable subsequent use of the area or to reconstruct the former morphology. A few spectacular sinkholes brought the maintenance required to secure the surface to the public s attention. In order to establish the long-term stability of insufficient backfilled shafts and near-surface extraction fields, highperformance technologies have been developed to be flexibly tailored to the specific requirements in each case. It is the same with the remediation of mine dumps and tailing ponds. For the reasons mentioned above, the mining authority NRW and numerous mining companies established a riskmanagement program (Hegemann, 2014). With Figure 7 one can summarize all the challenges with the former and the actual mining process in the Ruhr area. The cross section is generally useful to illustrate the tasks in the post mining process. FIG 7 Schematic cross-section through the hard coal deposit of the Ruhr ( Bezirksregierung Arnsberg, edited). Not only in urban agglomerations like the Ruhr area a stakeholder orientated sustainable land management (SLM) is an additional challenge (Kretschmann, 2014). It tries to combine the different interests of the stakeholders in this area to create win-win-situations in a sustainable context. The ecological, social and economical change of this former heavy industrial region can serve as a role model for SLM in urban areas all over the world. Besides this, the experiences in the Ruhr area are showing that the past is not necessarily a burden but can be a precious heritage to enhance towards the future. The three-dimensional approach to sustainability can easily be transferred to mining and post-mining activities of today: sustainable management of the mining impact means that environmental damage caused by emissions, subsidence and such can be limited (environmental dimension); the cost of managing both mining damages and perpetual tasks can be kept as low as possible (economic dimensions) and the population living in the mining regions can be offered future prospects to ensure their standard of living and their wellbeing after mining has come to an end (social dimension). VI. RESEARCH INSTITUTE OF POST-MINING The Research Institute of Post-Mining is an integral part of the University. While the institute has its own set of specialist core skills, the diverse disciplines that are practised within the wider University - which has traditionally had a high mining content - help create an interdisciplinary network (Melchers and Goerke-Mallet, 2015). As a result, the complex issues associated with the post-mining society can be tackled in a multi- and interdisciplinary way, thereby providing the central platform for the Research Institute. As well as having its own University-based interdisciplinary set-up the Research Centre also has access 290

5 to a comprehensive network of mining and former mining companies, public authorities, water boards and regional associations, industry organisations, consultative and administrative bodies and higher education establishments. The broad-based network also includes international contacts, as the challenges facing post-mining societies have a global relevance. There is now real interest in the global debate on the best approach to be used when closing a mining facility and ensuring transparency. Research is the main task of the Post-Mining Research Institute institutes work, with the long-term liabilities left by the coal industry provide the special focus of attention. These activities are centred around the key problem of mine water, which creates a whole range of issues associated with rising water levels. Against this background, the research activities of the Post-Mining Research Institute at the University of Applied Sciences TFH Georg Agricola Bochum focus on the flooding of underground openings, water bearing adits, subsurface mine openings and on international experiences with mine closure. Very important is an efficient monitoring of the post-mining processes. Besides local investigations, it is absolutely necessary to have spatial data. Impact studies based on 'Experiences with rising minewater levels in the disused coalfields of Germany and Europe' are currently under way. This including an assessment of the flooding process as it affects certain individual areas (Goerke-Mallet and Drobniewski, 2013). A survey is also being carried out of the bottom levels and water-bearing galleries of the Ruhr coalfield, along with separate investigations aimed at acquiring a temporal and spatial understanding of the density stratification in flooded mine shafts (Melchers et al., 2015a and 2015b). Innovative concepts for monitoring the rise in mine-water levels are also being examined and studies are under way into mine-water treatment and purification. Investigations are also being conducted into gas migration as mine-water levels rise and into the fundamental permeability of hydraulic barriers (Coldewey et al., 2014). The findings from this research work will help enormously in providing a record of rising mine-water levels and improving our basic understanding of this process. The provision of the security of the surface in old mining areas yields a major challenge (Goerke-Mallet et.al., 2016). To establish a successful re-use of the influenced areas, it is necessary to avoid instabilities above shafts, adits and subsurface mine openings. According to court decisions of recent years the last mining operator is obliged to deal with the whole post mining process. At this point monitoring measures come into focus. The European Union and the European Space Agency established the satellite mission program Copernicus. Copernicus builds up a modern and strong infrastructure for monitoring the earth and for geoinformation services. The task of this project is to supply the experts with remote sensing data. Seven satellites will be developed especially for this mission. The name of the satellites is Sentinel. The earth observation satellites Sentinel-1 and Sentinel-2 have been in operation since 2014 and FIG 8 Sentinel 1 and 2 ( esa, DLR). In cooperation with other partners the Research Institute of Post-Mining is working on the application of satellite data for remote sensing and monitoring of current post-mining processes. Particular emphasis is placed on the hydrochemistry of water bodies, the soil water content, the land use and the land coverage. With respect to the potentials of the Copernicus-program and the reliability of the data provision, the connection between information provided by the satellites and terrestrial expertise, will lead to an innovation of monitoring. As a consequence, it will be able to reduce post-mining risks and increase post-mining chances like the valorisation of mining infrastructures for the recovery of renewable energy. VII. CONCLUSION Mining activities lead to worldwide challenges after their ending, which are often marked by similar problems. Besides a variety of risks, numerous existing opportunities of postmining should be exploited. In this context, the Research Institute of Post-Mining at the University of Applied Sciences in Bochum works on strategies for environment friendly, sustainable and economical handling of all aspects of old- and post-mining. This includes intensive study of existing experience on the closure of mines and the risk management. Not only for the Ruhr deposit, but also numerous other mining areas worldwide, the development and deepening of knowledge on the optimisation of closure processes is important for environmental and financial reasons. The projects of the Research Institute are designed to provide information about chances and risks in managing planned flooding of underground mine workings in different settings in the foreseeable future. This includes dealing with former extraction fields and proposing solutions for an environmentally compatible purification of mine water. 291

6 The current domestically sourced production of raw materials covers approximately 70% of the total demand for resources in Germany. Germany remains a mining country with an extensive sector of old mining. In a region with such a high population density, the old mining sector creates special risks for the safety of the ground surface, the population and the environment. Unstable abandoned mine openings and sub-surface mine workings, uncontrolled methane emissions and acid mine drainage must be considered. One subject of the ongoing research at the Research Institute of Post-Mining at TFH Bochum is risk management for post-mining and the optimisation of closure processes in the mining industry. Thus, the environmentally compatible flooding of the underground mines of the largest German hard coal region, the densely populated Ruhr-area, is to be planned and accompanied by an efficient monitoring program. Beyond pit water management, the so-called perpetual obligations include extensive polder measures and groundwater purification. The specific need for action in this context is also spurred by European regimentations. There is a global need for environmentally compatible closure and safekeeping methods. The objective should be to enhance the transparency of communication on this subject in order to transfer specific pre-existing know-how across distinct mining regions all over the world. An important element is the international exchange of experiences. the Annual Meeting of the Society for Mining, Metallurgy & Exploration, Seattle, Washington, USA. Red Hook, NY: Curran Associates, Melchers, C. and Goerke-Mallet, P., Research Institute of Post- Mining, TFH Georg Agricola University of Applied Sciences, Bochum Strategies, Activities and Research Priorities. Mining Report 151, Melchers, C, Goerke-Mallet, P., Henkel, L., Hegemann, M., 2015a. Experiences with mine closure in the European coal mining industry: Anoverview of the situation in Germany, and adjacent regions. Mine Closure Conference, Vancouver, Canada. Melchers, C, Goerke-Mallet, P., Henkel, L., Coldewey, W.G., Wesche, D. 2015b. Density stratification in mine water bodies as a contribution to better long-term water management. Mining Report REFERENCES Coldewey, W. G., Wesche, D., Rudolph, T., Melchers, C., Methods for evaluating the hydraulic barrier effects of the Emscher Marl following the cessation of coal mining in Germany. An Interdisciplinary Response to Mine Water Challenges. Proceedings of the 12th Congress of International Mine Water Association, Goerke-Mallet, P. and Drobniewski, M., Planning long-term minewater management for the Ibbenbüren coal basin, in Deutscher Markscheider-Verein e.v. (DMV) (ed), Proceedings XV International ISM Congress, (International Society for Mine Surveying), Aachen, September 2013, Goerke-Mallet, P.,Mersmann, F., Beermann, T., Stöttner, M., Optimizing long-term mine water management of mining sites with the help of directional drilling and liner technology. Mining Report 152. Hegemann, M., Support of Solving the problems of Abandoned Mining Areas in Germany by Improvement of the University Education. Proceeding Book, pp 48-54, 33rd International Conference on Ground Control in Mining (China 2014), Beijing, China Kretschmann, J., Stakeholder orientated sustainable land management: The Ruhr area as a role mod-el for urban areas. Vestnik 02/2014: Kretschmann,J., The Sustainable Development Strategy of the German Hard Coal Mining Industry. 7th SDIMI conference, University of British Columbia, Vancouver, British Columbia. Kretschmann, J. and Hegemann, M., New chances from old shafts. Risk management in abandoned mine sites in Germany. In Proceedings of 292