This is the final post in the series on mapping in geothermal energy. We will focus on environmental and hazard mapping.  In order to make any geothermal development sustainable, we must reduce its environmental impact and mitigate potential hazards.  Even though emissions associated with geothermal exploration and development are small compared to fossil fuel power plants, there are other environmental concerns to be considered. The major environmental concerns associated with geothermal energy exploration and development includes:

  • Physical effects – Fluid withdrawal in natural manifestations, land subsidence, induced seismicity, visual effects/landscape modification, surface water;
  • Noise;
  • Thermal pollution (hot liquid and steam release on the surface);
  • Chemical pollution (liquid and solid waste disposal, gas emissions) and
  • Ecological protection Flora and fauna.

It’s good to note that the importance of each varies depending on the phase of geothermal development. For example feasibility- chemical pollution, visual effects, noise; plant construction – surface disturbances, noise, visual impact, ecological impacts and disposal of waste; and power plant operation – induced seismicity, subsidence, and noise.

Environmental mapping in geothermal energy includes land subsidence, impact on natural manifestations and induced seismicity (I will talk about induced seismicity seismic geo-hazards). Land subsidence associated with geothermal energy production can occur due to fluid withdrawal without balanced reinjection. We can map this using satellite interferometric synthetic aperture radar (InSAR) and from subsidence leveling surveys. InSAR has been recently applied to image structures with a lateral outflow of thermal fluids by showing areas of subsidence associated with fluid production and areas of uplift related to the injection. Land subsidence has been observed in New Zealand (max event 400mm/year,) and Tuscany, Italy (max event 250mm/y).

Image 1: Ohaaki, New Zealand contour map of average subsidence rates 1998 to 2006 (From Bromley et al 2015).

Geothermal production can impact natural manifestations due to subsurface pressure changes. This can result in a decrease or increase in the activity of thermal manifestations. Examples of increase thermal manifestation include Craters of the Moon, (Karapiti), Wairakei and Mokai, Tirohanga Road Craters in New Zealand. An increase in soil temperatures has been observed in Reykjanes, Iceland. Monitoring of thermal manifestations have been carried out using thermal infrared imagery (TIR) and an example from Iceland can be seen below.

Image 2: TIR image of the geothermal area in Reykjanes, Iceland, May 2011. (From Óladóttir, 2012)

Most medium to high-temperature geothermal resources are located in tectonically active regions. Thus increasing the chances of geo-hazard occurrences. These are hazards related to geological phenomena and includes, seismic and volcanic events and mass flow movements (landslides and debris flows). Geo-hazard mapping is important in order to identify potential hazard zones and aid in the development of mitigation measures.

Seismic events are related to ground motions caused by earthquakes (natural or induced). Hazard mapping and analysis of these events try to determine the location of potential earthquakes, identify past events, locate active faults and potential areas of associated hazards (landslides, liquefaction and ground deformation). On January 13th, 2001, a magnitude  7.6  earthquake was recorded in El Salvador which affected the Ahuachapán and  Berlín.

Reinjection of water into the reservoir or hydraulic fracturing (for Enhanced Geothermal Systems, EGS) can induce seismicity. Seismic monitoring has been done and is recommended for producing geothermal fields. This often results in a seismic map showing distribution, intensity, and location of seismic monitoring stations. Induced earthquakes occurred in Switzerland on two occasions:

  1. Basel (2006) associated with EGS reservoir stimulation which resulted in 4 seismic events with magnitude > 3;
  2. St. Gallen (2013) associated with hydrothermal resources in sedimentary rocks which generated a 3.5 magnitude quake during a well control sequence following a blowout.

A protocol for handling induced seismicity due to EGS can be found here.

Image 3: Induced seismicity at sites of geothermal projects Soultz‐sous‐Forêts, Landau i. d. Pf. resp. Insheim, Unterhaching, and Basel (red circles) in comparison with natural tectonic earthquakes (white circles) from June 2000 to March 2011, Switzerland. (From Grünthal, 2014)

A volcanic hazard refers to any potentially dangerous volcanic process (e.g. lava flows, pyroclastic flows, ash). Typically, volcanic hazards increase the closer we are to an eruptive center. However, in the case of a geothermal power plant,  we have to consider long-range associated events with these hazards such as ash falls and ballistic impacts (volcanic bombs and blocks). Understanding and mitigating these hazards require mapping past events (locations and affected zones), constant monitoring of volcanic activity and development of an emergency management plan. The most recent event was the eruption of the Kilauea Volcano that began on May 3, 2018. It resulted in the closure of the Puna Geothermal plant (Ormat Technologies) where lava eventually damaged numerous buildings, blocked an access road and covered 3 geothermal wells.

Mass movements are described as movements of soil and rock debris down slopes in response to the pull of gravity. These are affected by a number of internal and external factors. Internal factors include rock type; slope angles; altered ground; and the presence of faults. External factors include heavy rains, seismic and volcanic activities. A number of movements exist, the most common in geothermal areas are landslides and rockfalls. On January 5, 1991, a deadly landslide occurred at the Zunil I geothermal field (Western Guatemala) covering an area containing active fumaroles, access road and drill pad for one of 6 productions wells in the field. In order to mitigate against such events, detailed surficial geology and slope stability maps are necessary. This should also include information on landslides scars, alteration zones, faults, fractures, etc. Landslide hazard zonation maps have been created and an example from the Mindanao Geothermal Production Field in the Philippines can be seen below. The selection of drill pads, siting of buildings and layout and construction of steam pipes should avoid areas of the obvious potential for these hazards.

Image 4: Landslide hazard zonation map of the Mindanao Geothermal Production Field, the Philippines showing slope failure potential rankings. (From Pioquinto and Caranto 2005)

Even though the environmental impacts of geothermal energy utilization is small, there are still environmental impacts to be considered and managed. Here I covered those aspects that we can ‘map’, but others exist that focuses on showing data using charts and graphs. Geo-hazards can be natural or induced and can have severe impacts on geothermal utilization like in Zunil, Guatemala, and Switzerland. This shows the importance of environmental and hazard mapping including monitoring for geothermal exploration and development.

This concludes our series on mapping as an important tool in geothermal energy exploration and development. We hope that you enjoyed the series and learned something you can apply to your geothermal project. If you have any questions or comments feel free to contact us here or directly at [email protected].

For more #GeothermalFactsandStats check back here weekly and follow us on all our social media platforms.

 

References:

Barrios,L., Hernández, B., Quezada, A., Pullinger, C., 2011, Geological Hazards And Geotechnical Aspects In Geothermal Areas, The El Salvador Experience, Presented at “Short Course on Geothermal Drilling, Resource Development and Power Plants”, organized by UNU-GTP and LaGeo, in Santa Tecla, El Salvador,  January 16-22, 2011, 14 pp, https://orkustofnun.is/gogn/unu-gtp-sc/UNU-GTP-SC-12-46.pdf Accessed on April 08, 2019.

Berrizbeitia, L. D., 2014, Environmental Impacts Of Geothermal Energy Generation And Utilization, Volcanoes of the Eastern Sierra Nevada –G190, Hamburger, Rupp and Taranovic, June 16, 2014, https://geothermalcommunities.eu/assets/elearning/8.21.Berrizbeitia.pdf, Accessed on April 08, 2019.

Bromley, C.J., 2005, Advances in Environmental Management of Geothermal Developments, Proceedings World Geothermal Congress 2005  Antalya, Turkey, 24-29 April 2005, 7 pp, https://www.geothermal-energy.org/pdf/IGAstandard/WGC/2005/0236.pdf Accessed on April 14, 2019.

Bromley, C.J.,  Currie, S., Jolly, S., Mannington, W., 2015, Subsidence: an Update on New Zealand Geothermal Deformation Observations and Mechanisms, Proceedings World Geothermal Congress 2015 Melbourne, Australia, 19-25 April 2015, https://pangea.stanford.edu/ERE/db/WGC/papers/WGC/2015/02021.pdf Accessed on April 14, 2019.

Grünthal, G., 2014, Induced seismicity related to geothermal projects versus natural tectonic earthquakes and other types of induced seismic events in Central Europe. – Geothermics, 52, p. 22-35 DOI: http://doi.org/10.1016/j.geothermics.2013.09.009, http://publications.iass-potsdam.de/pubman/item/escidoc:272247:9/component/escidoc:682911/272247.pdf Accessed on April 14, 2019.

Flynn,T., Goff, F., Van Eeckhout, E.,  Goff, S., Ballinger, J.,  Suyama, J., 1991, Catastrophic Landslide At Zunil I Geothermal Field, Guatemala January 5, 1991, Geothermal  Resources  Council TRANSACTIONS, Vol. 15. October 1991, 10 pp, http://pubs.geothermal-library.org/lib/grc/1002159.pdf Accessed on April 14, 2019.

Majer, E., Nelson,J.,  Robertson-Tait, A., Savy, J., and Wong, I., 2012, Protocol for Addressing Induced Seismicity Associated with Enhanced Geothermal Systems, United States Department of Energy, Energy Efficiency and Renewable energy, Geothermal Technologies Program, 52 pp,  DOE/EE-0662, https://www1.eere.energy.gov/geothermal/pdfs/geothermal_seismicity_protocol_012012.pdf Accessed on April 11, 2019.

Ogola, P. F. A., 2005,  Environmental And Social Considerations In Geothermal Development

presented at Workshop for Decision Makers on Geothermal Projects and Management, organized by UNU-GTP and KengGen in Naivasha, Kenya, 14-18 November, 2005, 12 pp, https://orkustofnun.is/gogn/unu-gtp-sc/UNU-GTP-SC-01-15.pdf, Accessed on April 08, 2019.

Óladóttir, 2012, Application of soil measurements and remote sensing for monitoring changes in geothermal surface activity in the Reykjanes field, Iceland,  thesis submitted in partial fulfillment of a Magister Scientiarum degree in Geology, Faculty of Earth Sciences School of Engineering and Natural Sciences University of Iceland Reykjavik, July 2012, 128 pp, https://skemman.is/bitstream/1946/13001/1/LOKAUTGAFA.pdf Accessed on April 14, 2019.

Pioquinto, W. P. C.  and Caranto, J.A., 2005, Mitigating the Impact of Landslide Hazards in PNOC-EDC Geothermal Fields, Proceedings World Geothermal Congress 2005  Antalya, Turkey, 24-29 April 2005, 9 pp, https://www.geothermal-energy.org/pdf/IGAstandard/WGC/2005/0261.pdf Accessed on April 15, 2019.

Saemundsson, K., 2008,  Geohazards In Geothermal Exploitation, Presented at Short Course III on Exploration for Geothermal Resources, organized by UNU-GTP and KenGen, at Lake Naivasha, Kenya, October 24 -November 17, 2008, 7 pp, https://orkustofnun.is/gogn/unu-gtp-sc/UNU-GTP-SC-07-14.pdf, Accessed on April 08, 2019.

Wamalwa, H. and  Wetang’ula, G., 2012,  Environmental Impact Mitigation Considerations in Geothermal Drilling: A Case Study of Menengai Geothermal Drilling Project,  Proceedings of the 4th African Rift Geothermal Conference 2012 Nairobi, Kenya, 21-23 November 2012, 5 pp, https://www.geothermal-energy.org/pdf/IGAstandard/ARGeo/2012/Wamalwa.pdf, Accessed on April 08, 2019.

Wiemer, S., Kraft, T., Trutnevyte, E.,  Roth, P., 2017, “Good Practice” Guide for Managing Induced Seismicity in Deep Geothermal Energy Projects in Switzerland, Swiss Seismological Service (SED), 69 pp, http://www.seismo.ethz.ch/export/sites/sedsite/research-and-teaching/.galleries/pdf_products_software/Good-Practice-Guide-for-Managing-Induced-Seismicity-in-Deep-Geothermal-Energy-Projects-in-Switzerland_v1.0.pdf Accessed on April 13, 2019.

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