In rare cases the injection of water into the ground can unleash seismic activity. Unlike natural earthquakes, this type of induced seismicity can be controlled by regulating water pressure. This requires seismological monitoring, which has now become standard. Monitoring of seismic activity enables tracking its location and quick response. In general, the maximum magnitudes of induced seismic activity are significantly smaller than those in other areas of mining activity. If the precautionary measures as proscribed in the authorisation are taken, risks are neither likely nor severe.
Risks to groundwater used in the extraction of drinking water are unlikely with the applied methods and when applied in compliance with the regulations in mining law and observance of the legal provisions governing drinking water and groundwater. If disruptions occur as a result of leaky boreholes, these can be detected and are limited in their impact. At most, the natural deep groundwaters in the geothermal reservoir may be exposed to a certain risk potential. For example: the process of generating geothermal energy can, depending on region, also evacuate deep groundwater with high salinity along with other trace elements which affect drinking water hygiene. Existing standards must be observed in this regard, and the contaminated groundwater may require professional disposal on the surface. Operation of the geothermal plant itself involves a closed water circuit above ground, and thus no disposal of natural formation water is necessary.
Special preliminary investigations, monitoring and evaluation of all data are recommended for the planning and implementation of hydraulic fracturing. Future projects should be monitored closely and scientifically because of the as yet small number of existing plants. The study also gives recommendations for the establishment of seismic and hydrogeological observation stations. Sampling should commence prior to the installation phase. In sum, these are the requirements for establishing an effective early warning system which minimizes risks.
Methodology and database
The present survey and analysis are based on existing studies and unpublished information provided by operating companies from Germany and from neighbouring countries.