Althought, it is believed that the environmental impacts of geothermal energy are rather low compared to other resources, especially to fossil fuels., Geothermal energy does have some environmental considerations, including: Air and water pollution: Geothermal power plants can release small amounts of sulfur dioxide and carbon dioxide. However, they emit 97% less acid rain-causing sulfur compounds and about 99% less carbon dioxide than fossil fuel power plants of similar size. Land subsidence: As plants remove water and steam from underground reservoirs, the land begins to sink over time,... Show more

Althought, it is believed that the environmental impacts of geothermal energy are rather low compared to other resources, especially to fossil fuels., Geothermal energy does have some environmental considerations, including:
Air and water pollution: Geothermal power plants can release small amounts of sulfur dioxide and carbon dioxide. However, they emit 97% less acid rain-causing sulfur compounds and about 99% less carbon dioxide than fossil fuel power plants of similar size.
Land subsidence: As plants remove water and steam from underground reservoirs, the land begins to sink over time, altering vegetation and wildlife. However, most geothermal plants reinject geothermal waters back into the earth to reduce this.
Water use: Geothermal plants use water and steam as fuel, but they use less water than coal, oil, or nuclear plants.

Drilling: The impact of drilling can still affect wildlife and surrounding areas. 

And also:
Hazardous waste disposal
Siting
Noise and sight pollution
Production of foul odors
Soil subsidence
Surface instability

Related: Renewable Energy Practice Test: Geothermal Energy & Applications

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