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Fig. 1. Greater transparency between the scientific community and society (from left to right): BIK Chairman Holger Perrevort, Mayor Rainer Doetkotte, Prof. Tobias Rudolph from the FZN and Andreas Müterthies from EFTAS sign the new research cooperation at the edge of the cavern field. Photo: THGA

What is causing the ground motion in Epe cavern field?

The ground below Gronau and the surrounding area is a challenge, even for geologists: Salt has been mined here intensively for almost 50 years. This has created large cavities, known as caverns, at depths of between 1,000 and 1,500 m. Most of them are now used to store natural gas, crude oil or helium, and are important to the economy of the entire region. Right next to this cavern field is Amtsvenn nature reserve, spanning 9 km2 of moorlands.

This special place has been the frequent source of tension over the years – not only in the geological structures themselves, but also between residents, the city and the various operating companies. The main cause of this tension is the ground motion, which in the long term could lead to subsidence in the area and consequently cause damage to buildings and alter the water balance. But what is actually caused by mining? And what is caused by nature? This is where a new, unique research cooperation, formed to investigate Epe cavern field, comes in. The new cooperation includes the City of Gronau, the citizens’ group Bürgerinitiative Kavernenfeld Epe e.V. (BIK), EFTAS Fernerkundung Technologietransfer GmbH and the Research Center of Post-Mining (FZN) at TH Georg Agricola University (THGA) in Bochum (Figure 1). Together, they want to find a solution to determine where the ground motion in the cavern field is coming from. “In order to understand the processes in detail, it is crucial to carry out tailored, extensive monitoring of all factors that are having an impact on ground motion in the region,” explains Prof. Peter Goerke-Mallet from the FZN. This includes satellite data from Copernicus, the EU’s space programme, as well as the use of local infor-mation and the knowledge of residents.

“Above all, we want to use this new research cooperation to establish a foundation of trust,” says Prof. Goerke-Mallet. “Today, all mining projects require transparency and the extensive sharing of expertise with society and vice versa. In this project, we can benefit from the knowledge of local people in a really special way,” says the experienced mine surveyor and mining expert. “After all, the residents know best where the challenges lie in their local area and can observe and document the changes in the landscape and buildings, sometimes even over years and decades. The research cooperation for Epe cavern field therefore offers a highly innovative approach to conflict resolution through active participation.”

Holger Perrevort, chair of the citizens’ group, also hopes that the cooperation will improve the flow of information and create more opportunities for involvement. “Above all, we want more accurate information about what is happening right below our very feet.” A lot has gone wrong here in the past, according to the resident. Not enough attention was paid to the potential risks and impact of ground motion, Perrevort says. “As a citizens’ group, we have been fighting for our concerns to be taken seriously for years already. Politicians must also fulfil their duty of care towards residents, e. g., if cellars get wet or cracks appear in walls.”

The experts at the FZN in Bochum also want to get to the bottom of this damage. Over the next twelve months, they will perform specific measurements to investigate the issue – using drones, which can detect changes in vegetation, e. g., and satellite data, which the specialists from EFTAS in Münster will analyse. “But we will also make a deliberate effort to visit the locals, to conduct building inspections and measure buildings and properties that may have been affected by ground motion,” explains Prof. Tobias Rudolph, a geomonitoring expert at the FZN. “Close cooperation with local residents is vital for us to be able to complete this work, so we are extremely grateful that new doors have been opened to us in this respect – in the truest sense of the word.”

The scientists are likely to spend most of their time analysing the large volume of data: “We will examine information on the groundwater and the surrounding bodies of water, on the ground, the subsurface and the caverns, among other things.” Their contact with members of the citizens’ group and the city also gives them access to many other important sources of information, such as private measuring points, springs and municipal geodata, which they plan to link together and analyse. Naturally, this will not all be done behind closed doors, but rather – in keeping with the pursued aim of transparency – alongside regular information events, where the results will be freely disclosed and discussed.

This planned approach also convinced Rainer Doetkotte, the Mayor of Gronau, to add his signature. Most importantly, he can envisage the positive effects this cooperation will have on the region in the long term: “This research cooperation marks the start of an important project, and I am delighted that we have the FZN, EFTAS and BIK on board for it. Ultimately, we want to provide the interested public with detailed information using the results obtained, in order to resolve any concerns, dispel any prejudices and increase acceptance within society. The results can also be used to create other concepts in the future, bringing further scientific progress to Gronau.” (THGA/Si.)