1) Depletion of resources. Geothermal fluid extraction for the generation of electricity typically involves the removal of heat from reservoirs, at a rate that is about 10 times of their replenishment rate. This includes removing water, steam, and gases. However, it is possible to improve the resulting imbalance by injecting the geothermal system with waste fluids. This impact can therefore be mitigated.
2) Geothermal features damage. This is one of the biggest environmental impacts of geothermal energy. Geothermal development can damage natural features like geysers, mud pools, hot springs, sinter terraces, steaming ground and fumaroles (steam vents). This damage can be irreparable. For example, the great Wairakei Geyser has already vanished in Geyser Valley, which once shot up to a height of 42 meters.
3) Subsidence. When geothermal fluids are extracted, the underground reservoir pressure is reduced, which makes the land sink. When this happens, the ground also tends to tilt toward the center, as it moves sideways. This puts a strain on pipelines and could cause damage to roads and buildings. It could also change patterns of surface drainage. This is not normally a big problem though as geothermal energy is extracted in rural areas.
4) Waterways pollution. Another one of the environmental impacts of geothermal energy is the potential pollution factor. Geothermal fluids contain mercury, boron, lithium, and arsenic at elevated levels. This is because of the contact geothermal water has with underground rocks. If this water gets released into lakes and rivers, there may be damage to aquatic life, and the water may become unsafe for irrigation and drinking.
5) Air emissions. There are dissolved gases in geothermal fluids that may be released into the atmosphere. The main toxic gases are hydrogen sulfide (H2S) and carbon dioxide (CO2). These gases are classified as a hazard for urban areas, and especially for workers in bore fields and geothermal stations.
6) Issues with water and wells. Another concern with geothermal energy is the potential depletion of aquifers if they are not reinjected with water. Also, there is an issue with wells that are not properly installed, which may create a surface run-off path that may carry fertilizers, pesticides, and various contaminants into aquifers.
7) CFC and refrigerant issues. Geothermal heat pumps on the current market use modern refrigerants, which are potential leak sources. These leaks may be harmful to the environment, as refrigerants should never be released into the atmosphere. They are a hazard when not handled carefully and correctly.
Having said all this, it is still important to acknowledge the endless benefits of geothermal energy. These environmental impacts are minor compared to the advantages geothermal energy has over fossil fuels (which are much more hazardous than geothermal fluids). In addition, the majority of these impacts can be mitigated, and their actual impact can be very small. Geothermal remains quite possibly the source of renewable energy with the most potential as of now.
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