A series of minor human-induced earthquakes in the area of Strasbourg, eastern France, last December has reminded local inhabitants about the safety of geothermal energy, highlighting the challenges faced by deep drilling technology.
In December, the area around Strasbourg was shaken by several induced tremors, including one of 3.5 magnitude, after a geothermal company carrying out tests injected high-pressure water into the ground earlier in the autumn.
Induced earthquakes – those caused by human activity – had begun since tests started in the Alsace region in October at the geothermal plant operated by Fonroche, a French energy company.
The tremors were directly linked to the starting-up activities of the plant, said the French association of geothermal professionals, the AFPG.
“It appears that seismicity related to deep geothermal in Rhine Basin geologic reservoir is mainly associated with testing phases during drilling and starting-up operations,” AFPG said in a statement. “This seismicity is measured and monitored all along the construction and operating phases during which events are generally not felt,” it added.
Fonroche, the company operating the plant, confirmed to AFP that the shock was linked to its activities. In a statement, it said the December episode “could be a continuation of the movements induced by the tests undertaken” in October but was “also taking place in a context of intense seismic activity on the West European ridge for several weeks”.
The Alsace region is prone to natural tremors and has put in place a seismic plan to better map the risks and inform the population.
Several geothermal plants are already operating there, without causing major seismic activity to date. Tests on geothermal plants that use a technology called enhanced geothermal systems (EGS), can cause tremors, but those are controlled and usually don’t go above a level of 2 on the Richter scale.
For the geothermal industry, the tremors in December, which hit a level of 3.5 on the Richter scale, were “exceptional”.
“We see this as an excuse for people to say no to geothermal,” said Sanjeev Kumar, head of policy at the European Geothermal Energy Council (EGEC), an industry body. “For decades, we’ve been going ahead of the curve in terms of how we manage this,” he told EURACTIV.
After the December tremor, the French authorities requested the operator to close the plant. This started a progressive and total shutdown of the geothermal fluid circulation between the 5km-deep boreholes, which caused another 2.8 magnitude earthquake on 10 April.
According to Fonroche, those will stop once the plant is fully operational because the water pressure will be constant.
An investigation is ongoing into how and why the tremors were caused. Earthquakes were already registered in October and November 2019, including a 3.1 magnitude one thought to have been induced. The French government and Fonroche carried out scientific tests to discover the origin of these, which could also explain the December 2020 earthquake.
The plant, due to be France’s most ambitious geothermal project, was a €90 million investment that would supply 15,000-20,000 homes with electricity and 26,000 with direct heat as well as mine lithium.
The geothermal unit was built in the same area as a recently decommissioned nuclear power plant, in Fessenheim. And in the run-up to the French regional elections in June, some have questioned the timing of the test.
“There are questions over the timing of the incident, and who were the people who made the decisions,” said Kumar.
‘Confidence has been shattered’
The village of La Wantzenau near Strasbourg was particularly affected, with 450 insurance claims.
“There is significant damage. It is an attack on heritage,” said the mayor of the village, Michèle Kannengieser, adding the tremors caused a collective fear.
“We no longer believe in [the project], and we are not ready to believe in it again. I think that no demonstration today, however scientific, will be able to modify our position, which seems to me to be very legitimate,” she added.
Because it was not a natural disaster, people who are not insured have been forced to take direct action against Fonroche. According to Kannengieser, this has been hard to deal with for the victims.
“People are still not cured of this fear and it remains an extremely sensitive subject. In this village, there are many single people, elderly people, who have quite large cracks [in their walls] and who are alone in defending their interests,” she said.
According to the French industry association, the incident does not bring into question the wider benefits of deep geothermal for the energy transition.
“Those seismic events do not question the relevance of deep geothermal projects in such geological framework, as they remain a renewable and emission-free technology for the energy transition,” said AFPG, pointing to several power plants already operating in the Rhine Basin.
According to EGEC, there are over 150 geothermal power plants in operation and more than 300 direct heating geothermal projects in Europe, which have all met environmental impact assessments.
Philippe Dumas, secretary-general of EGEC, said the incident in Strasbourg shows the need for higher levels of public engagement and sharing of best practices across Europe. “The aspect of communication and public engagement is really part of best practices,” Dumas said.
But for the local authorities in Strasbourg, the incident does raise fundamental questions.
“Geothermal energy has the advantage of rapid conversion. With one project, we can convert tens of thousands of homes into heating. It is also an energy source with a stable and competitive price for the user,” said Marc Hoffsess, the deputy mayor of Strasbourg.
However, he admitted that the industry’s development in the region is now likely to be stopped in its tracks.
“Confidence in the operator, Fonroche, and also in deep geothermal energy, has been completely shattered. The psychological impact is very strong and this will be the first condition for the rehabilitation of deep geothermal technology,” Hoffsess said.
[Edited by Frédéric Simon]