Geothermal Environmental Impact
The impact that geothermal energy has on the environment depends on the type of cooling and conversion technologies used. Environmental impacts are often discussed in terms of:
- Water Consumption
- Geothermal power production utilizes water in two major ways. The first method, which is inevitable in geothermal production, uses hot water from an underground reservoir to power the facility. The second would be using water for cooling.
- Geothermal Air Emissions
- When considering air emissions knowing whether a power plant is a closed loop or an open loop makes a significant difference. In closed loop systems the gases from inside of the well are never exposed to the atmosphere and therefore end up back inside the geothermal reservoir. In an open loop system steam as well as any other gases in the reservoir are emitted into the atmosphere. Not every reservoir is the same and therefore the gases that may be emitted are different at every location, but some common gases found in geothermal reservoirs are: Hydrogen Sulfide, Carbon Dioxide, Ammonia, Methane and Boron. The most common of the emitted gases in geothermal power plants is Hydrogen Sulfide.
- Air pollution from geothermal power plants are significantly lower than those from an average US power plant. Geothermal plants are responsible to less than 5 percent of non condensable gas emissions. Tables below summarize air emission information provided by EPA website.
- Geothermal Land Use
- The amount of land required for a geothermal power plant depends on many factors including, but not limited to; reservoir size, conversion technology, temperature of geothermal water, cooling requirements, and building needs. The Geysers Geothermal field in California is the world's largest geothermal area comprising 15 individual power plants that net 725 MW of electrical production. The facility is about 45 square miles (28,800 acres) which equates to about 16 MW/square mile (25 kW/acre). 
- Life-Cycle Analysis Results of Geothermal Systems in Comparison to Other Power Systems Argonne National Lab, 2010.
- Life-Cycle Analysis of Geothermal Technologies Argonne National Lab, 2010. (Presentation)
- Environmental Impacts of Renewable Technologies
- EERE Geothermal - Environmental Impacts, Attributes, and Feasibility Criteria
- Promoting Geothermal Energy: Air Emissions Comparison and Externality Analysis
When discussing environmental impacts from a regulatory perspective, different topics are discussed. Most NEPA documents (Environmental Assessments (EA) and Environmental Impact Statements (EIS)) have similar topics of discussion, including:
- Cultural Resource Assessment
- Any project that requires the developer to disturb the surface has the potential to uncover cultural resources. Cultural resources include objects or sites that have historical, cultural, or archaeological value. Specifically, the Native American Graves Protection and Repatriation Act includes human remains, funerary objects, and sacred objects. Discovery of cultural resources during any stage of development will usually require operations in that area to cease and certain parties to be notified. Potential parties may include the State Historic Preservation Office for federal lands and the county coroner/state archaeologist at the state and local level.
- Flora and Fauna Resource Assessment
- In choosing a potential geothermal development site, the developer must consider the presence of protected plants and animals. The potential to disrupt or destroy the natural habitat of any such species could add significant delays to the development timeline. At the federal level, important statutes include the Endangered Species Act, the Migratory Bird Act, and the Bald and Golden Eagle Protection Act. Statutes and regulations regarding flora and fauna at the state and local level vary but often concern development in state wildlife areas.
- Assessment of Impact on Previous Land Uses in the Area
- Land use assessment describes a process that includes onsite inspection of the potential development site to identify and a evaluate site-specific concerns and requirements. This process will usually take into account the presence of any local land use plan and whether the development of a geothermal energy production facility will be consistent with that plan.
- Water Quality Resource Assessment
- A geothermal project will inevitably have an impact on the water resources around it. The Clean Water Act (CWA) is the major federal statute in this area. Under the CWA, states are required to classify bodies of water by their intended uses and develop plans to ensure those bodies of water meet certain ambient water quality standards. In addition, under the CWA, the National Pollution Discharge Elimination System (NPDES) issues permits for the discharge of a pollutants into waters of the United States. States and localities may also have statutes and regulations related to water quality. It is the developer's responsibility to be aware of the water quality standards in the area and adopt protocols to control discharges into local water resources including stormwater runoff.
- Air Quality Resource Assessment
- A geothermal project will most likely have an impact on the air quality in the immediate area, whether through construction or operation. The Clean Air Act (CAA) is the major federal statute regarding air quality. The CAA directs the Environmental Protection Agency (EPA) to develop regulations aimed at preserving and improving air quality in the United States. The parts of the CAA that are most relevant to the geothermal developer are Title I: Programs and Activities and Title V: Permits. Title I controls air permits for construction and specific minor sources. Operating air permits are issued under Title V. Under the CAA, states are free to enforce stricter air quality standards and many issue their own air permits.
- Geological Resource Assessment
- The geothermal developer must also be aware of any potential impacts on geological resources, including soils and paleontological resources. Projects in certain areas may also impact protected cave systems and rock formations. In these situations, the appropriate permits must be acquired to continue development.
- Aesthetic Resource Assessment
- On federal land, the BLM is required to take scenic value into account in its management of those lands. Under the Federal Land Policy and Management Act requires the BLM to assign land areas to classes based on an objective scenic value determination. The class to which a certain area is assigned may serve as part of the baseline for National Environmental Policy Act (NEPA) evaluations. At the state and local level, aesthetic concerns may also form part of the land use and permitting policy for a given area.
- Waste and Hazardous Material Assessment
- The use of above ground or underground storage tanks and the storage, treatment, production, disposal, or discovery of hazardous waste onsite will require the geothermal developer to obtain certain permits. The EPA authorizes individual states to permit storage tanks. The Resource Conservation and Recovery Act (RCRA) controls permitting for the treatment, storage, and disposal of certain hazardous wastes. The discovery of hazardous waste onsite will trigger the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) which is tasked with the clean up of such sites.
Geothermal Regulations and Permitting for Environment
For information about regulations and permitting related to environmental considerations for geothermal projects, see the Regulatory and Permitting Information Desktop Toolkit.
- "GEA (2007) - A Guide to Geothemral Energy and the Environment"
- "The Geysers - About Geothermal Energy"
- "NREL - Renewable Electricity Futures Study"
- "NREL - A Review of Operational Water Consumption and Withdrawal Factors for Electricity Generation Technologies"
- "GEA (2008) - The State of Geothermal Technology"