Problems with public acceptance of geothermal projects and, the possible annoyance that they could cause are known obviously known from the experience of numerous projects in Europe. As it is sometimes difficult to avoid any disturbance during the development of a geothermal site, it is important to try to either minimize them or to deal with people’s fear.
The main problem that we have to face at Soultz is related to induced seismicity. We performed 4 massive hydraulic stimulation tests between 2000 and 2005. During each experiment around ten earthquakes reached a magnitude 2 or higher among the thousand of recorded events. The strongest event was of magnitude 2.9 and several other were above 2.6. Our experience shows that magnitude 2 is the threshold above which people begin to feel the induced earthquakes. The stronger ones provoked lots of troubles among the inhabitants. They were felt quite largely in the region around the site and, especially after the M=2.9 event, we had to face several complaints about presumed damages and a growing anger among population and local authorities. Knowing that induced seismicity is somehow unavoidable during hydraulic stimulation process, we take different measures to reduce the risk of getting any strong opposition from the population. Three different ways were followed: scientific, technical (both aiming at reducing the number and the magnitude of seismic events) and communication.
- Scientific: Focus was made on the understanding of the processes responsible for higher magnitude earthquakes (research studies by our partners, creation of an independent group of experts to evaluate the seismic risk, international cooperation). A permanent surface seismological network was installed by EOST. Additional accelerometers were installed by EOST to measure the effective acceleration of the ground at different locations around Soultz.
- Technical: Instead of achieving massive hydraulic stimulation, we try to act on the medium by performing chemical stimulations which are generally softer procedures. As fractures are sealed with hydrothermal deposits (calcite, silica, clays …), a testing program was built to define different proper chemicals to target each minerals. This allows reducing the injected flowrates and consequently the overpressure in the reservoir and thus leads to less numerous seismic events and no larger magnitude.
- Communication: Public information meetings were organized to explain what we were doing on the site and give information on earthquakes. Local authorities were also informed of each planned hydraulic experiment. A small macroseismic investigation was achieved after the 2.9 earthquake to collect information about how people felt the vibrations. One accelerometer was installed in the Gendarmerie buildings and another one in the cellar of one inhabitant’s house. Since then public information meeting are organized every 2 months and we noticed that a lot of participants are coming from the region around Soultz and are very interested and satisfied in knowing more about the project. Moreover, a regular 2-fold flyer written in three different languages is distributed and mailed to a large audience in order to increase the communication process. The web site is also regularly updated.
The extensive scientific studies, which helped to better understand the stimulation processes, the use of low seismicity-inducing tests and a better information to motivated population have contributed to significantly increase the social acceptability by producing a more quiet social environment around the project for 2 years now. And we hope that, once our project (and other) will run and that people will see concrete results, they will be able to make a better balance between the benefits given by a geothermal project and the possible disturbances that it could induce.