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An entire geothermal field uses 1-8 acres per megawatt (MW) versus 5-10 acres per MW for nuclear operations and 19 acres per MW for coal power plants. Coal power plants also require huge acreages for mining their fuel. These mining operations can involve large-scale movement of earth for construction of underground mine shafts and tunnels, waste heaps, and/or open pits. Disturbed surfaces from open pit mining also can limit plant life participation in the carbon cycle and evapotranspiration, which replenishes water in the atmosphere. Adequate remediation of strip-mined areas can be expensive too.
A typical geothermal power plant requires wells, and drilling them impacts the land. However, advanced directional or slant drilling technology has evolved, which minimizes the impact. This drilling technology allows several wells to be drilled from one location. This reduces the amount of land needed for drilling pads, access roads, and geothermal fluid piping.
For geothermal exploration, slimhole drilling can be used to minimize environmental impact. Slimhole wells are only 4-6 inches in diameter while traditional geothermal exploration wells have been 8-12 inches in diameter. Slimhole drilling also reduces the amount of land needed for site preparation and road construction.
Land subsidence can occur following the withdrawal of large amounts of fluid—water, oil, and even geothermal fluid—from beneath the earth's surface. The common practice by geothermal power plants to inject spent geothermal fluids back into reservoirs to sustain resources helps prevent subsidence from occurring.
Induced seismicity or earthquake activity also becomes a concern when large amounts of geothermal fluids are withdrawn and injected below the earth's surface, especially in areas with a high frequency of naturally occuring seismic events. If induced seismicity occurs, it's typically less than magnitude 2.5 on the Richter scale (earthquakes usually aren't felt below 3.5). Recently, some areas near The Geysers geothermal field in California have been experiencing increased seismic activity. There's concern that it could be due to wastewater injection—which helps replenish the geothermal resource—from the Lake County Sanitation District (LACOSAN). The U.S. Department of Energy, the U.S. Geologic Survey, and the geothermal power companies at The Geysers are monitoring this activity.
For more information about LACOSAN's effluent injection at The Geysers, see The Geysers Pipeline Project on the Geo-Heat Center Web site.
Other Land Uses and Landscape
Because of their minimal land use and impact, geothermal power plants also blend in harmoniously with a variety of other land uses. For example, once the geothermal power plant and associated wells are completed, the land can be used for livestock grazing or other agricultural purposes. The Imperial Valley of southern California hosts 15 geothermal power plants producing more than 400 MW of electricity within one of the most productive agricultural areas in the world. One of these plants—at the southern end of the Salton Sea—is neighbor to a national wildlife refuge that shelters hundreds of animal species. Visitors to Mammoth Lakes, California, enjoy many outdoor activities without even noticing the geothermal power plant in the area, which was designed to blend into the landscape.
In areas with natural hot springs and steam vents, proper siting of geothermal wells can minimize any impact to these scenic and recreational areas.