Seismicity
Induced seismicity, also known as manmade or induced earthquake, is associated with rather negative perceptions. Even when the probability of seismic events is considered low, the high perceived consequences may constitute a major concern (Knoblauch, Stauffacher, et Trutnevyte 2018; Benighaus et Bleicher 2019; Stauffacher et al. 2015; Manzella et al. 2018). Various main factors are known to influence perceptions of seismicity. Uncertainty about long term consequences of geological disturbance can create the perception that geological disturbance must be avoided as a principle (Knoblauch, Trutnevyte, et Stauffacher 2019). Also, unclarity about the use of technologies such as fracking have a major influence on perceived seismic risks (Benighaus et Bleicher 2019; Carr-Cornish et Romanach 2014). Furthermore, the siting of deep geothermal is key, the public preferring the implementation of deep geothermal in remote rather than urban areas to avoid the consequence of seismicity on buildings (Knoblauch, Trutnevyte, et Stauffacher 2019).
The perception of induced seismicity is further impacted by contextual elements and social dynamics. Accidents caused by induced seismicity like the one in Basel, Switzerland in 2006, greatly impacted public opinion fed by the negative discourse in media reports (Stauffacher et al. 2015; Kunze et Hertel 2017), which eventually led to the emergence of an environmental protest movement in Germany, and to the withdrawal of deep geothermal projects. National and local context may also alter the perception of induced seismicity. The environmental protest movement in Germany, for example, emerged in a context of overall protestation against nuclear power, carbon capture, shale gas and wind parks (Kunze et Hertel 2017).
Groundwater pollution
Several studies on public acceptance of deep geothermal carried out in Europe such as France, Italy, Greece, Germany, Switzerland, and outside of Europe such as in Australia and Chile continuously highlight that groundwater pollution is perceived as a dominant environmental concern by the citizens (Manzella et al. 2018). For example, in Québec, a survey showed that out of 1353 respondents, 58% of them put groundwater pollution as first environmental concern (Carr-Cornish et Romanach 2014). The literature is not always clear in what it is exactly meant by ‘groundwater pollution’, but it usually refers to the risks associated to water quality or the fear of poisoned water such as arsenic contamination (Vargas Payera 2018; Carr-Cornish et Romanach 2014; Chavot et al. 2018). Some of those concerns are triggered by a lack of knowledge or information on deep geothermal operation processes (Manzella et al. 2018; Carr-Cornish et Romanach 2014). They are also linked to past events such as the Basel seismic event in Switzerland, or by the collective memory of particular events concerning water, such as the contamination of water due to uranium mining activities conducted until the 1980s in Schneeberg/Bad Schlema, in Germany, which still impacts the lives of its citizens (Carr-Cornish et Romanach 2014; Benighaus et Bleicher 2019). A mismatch between local risks and global benefits can also be observed. For example, water usage concerns raised during the drilling phase remain mostly local concerns, compared to global benefits such as low emissions on the environment (Carr-Cornish et Romanach 2014). Overall, while demanding complete avoidance of human impact on the environment, some express the need for more research (Benighaus et Bleicher 2019).
Air emissions
The topic of air emissions shows more contrasted results in the perception of deep geothermal energy. They trigger the question of whether deep geothermal energy is a renewable energy or not. In Germany, in 65 arguments related to the most concerning environmental preoccupations, only 4 arguments questioned the environmental friendliness of deep geothermal in terms of CO2 emissions, and some participants even proposed some solutions, calling for more research or the responsibility to decrease CO2 emissions (Benighaus et Bleicher 2019). In contrast, there is a strong negative perception of air emissions when controversial cases associated to deep geothermal developments are made publicly known. For example, the case of the Milos pilot plant in Greece, and the case of the Mount Amiata in Italy. In Greece, fierce opponents to deep geothermal developments rose because of errors in the construction of the plant on the Milos Island, which lead to extensive air pollution (Karytsas, Polyzou, et Karytsas 2019). In Italy, a real organization of civil society emerged, and established itself as a social movement called the Amiata, advocating against the development of deep geothermal. This social movement is supported by the Italian 5 Star party, even supported by a few decision makers among European Institutions. The topic of deep geothermal development turned into a controversial situation concerning the emissions of Monte Amiata power plants, and the Amiata movement pledge their case before the court of Tuscany in 2018 (Pellizzone, Allansdottir, et Manzella 2019). They argue in their SOS Geotermia Manifesto that “each geothermal plant emit to the atmosphere, on top of steam, CO2, mercury, arsenic, sulfuric acid, ammoniac and other polluting steam causing severe damages to the environment and the health of its inhabitants (Mobertos 2015)”.
Surface disturbance: noise, vibration, dust, smell, land occupation, visual.
Disturbance can occur throughout the development of a deep geothermal plant. It includes noise, vibration, the land occupation, dust, smell, or the visual pollution. As noise occurs during the drilling and production processes, noise pollution is usually poorly perceived (Benighaus et Bleicher 2019). A survey carried out in 2012 in Soultz-sous-Forêts, France, highlights that it is not so much the presence of the plant that preoccupies but well the noise by 56.7% of the respondents (Chavot et al. 2019). In Switzerland, the noise pollution and the impact on landscape became such a public mater for the inhabitants of the Haute-Sorne that the case was introduced before the Court (Ejderyan, Ruef, et Stauffacher 2019). Concerning the vibration felt by the local residents, an empirical study in France (Richard, Maurer, et Lehujeur 2016) concluded the absolute necessity to avoid vibration felt by the population in order for deep geothermal operations to gain more acceptance.
Disturbance in the literature can also be linked to the location of the deep geothermal project. Several authors (Majer et al. 2012; Richard, Maurer, et Lehujeur 2016; Knoblauch, Trutnevyte, et Stauffacher 2019; Chavot et al. 2019) highlight that the location of the Enhanced Geothermal System technology “ in populated areas could be regarded by some as an intrusion on the peace and tranquility of populated areas due to its potential ‘annoyance factor’ (Majer et al. 2012 p.1)”. Some interviewees comment: “After reading all the information I think I would be ok if they were to start a project in my area, I am not sure how far they should be, far away enough that there is a minimal noise, traffic congestion, and an eyesore to the environment?” (Carr-Cornish et Romanach 2014, 1567). Disturbance due to the location and occupation of the land can also trigger lots of concerns and fierce opposition if there is disturbance to protected natural environment such as natural parks (Chavot et al. 2019).
Ground elevation
The perception of ground elevation is rather slim in the literature. Concerns were raised during one controversial event in Germany, in the city of Stauffen, where it was reported that the ground had lifted from 12 centimeters, caused by the drilling operations. It was concluded that the media reports frame and impact “what and how much people learn from the event presented” (Benighaus et Bleicher 2019, 53).
Radioactivity
Very little is known about the perception by the citizens of radioactivity in the development of deep geothermal plant. Nevertheless, during the legal public inquiry performed in France for the Alsace, Haute-Savoie and Reunion Island projects, it turned out that those legal public enquiries became real protest platforms, through which the radioactive upwelling was reported as one of the major environmental concern by the inhabitants (Chavot et al. 2019).