Deep geothermal energy: environmental risks can be controlled

Groundwater not at risk – seismic monitoring now standard

gush spring — **Gush spring: Geothermal energy is thermal energy generated and stored in the Earth.**
Source: kichatof / Fotolia.com

Deep geothermal energy holds no uncontrollable risks for the environment in Germany. These are the findings of a study done by the Federal Institute for Geosciences and Natural Resources (BGR) on the basis of an administrative agreement with the German Environment Agency (UBA). Deep geothermal energy originates from depths of 2,000 metres and more, where temperatures are higher than 60 degrees Celsius. In order to use this geothermal heat it is sometimes necessary to inject water at high pressure into those deep rock layers. This creates flow paths for the subsequent water circulation at the geothermal power plant. The method does not apply any materials which jeopardise the groundwater. The only exception is limestone, where diluted acids are sometimes applied, albeit in an environmentally compatible way. There is no risk from seismic activity in controlled processes.

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.

Further information

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.

Deep geothermal energy: environmental risks can be controlled | Umweltbundesamt

Joint press release by the German Environment Agency and the Federal Institute for Geosciences and Natural Resources