Geothermal/Water Quality

From Open Energy Information

Geothermal Water Quality

Water Quality
Present, Potentially Affected

Three federal statutes impact water quality at a geothermal site. They are:

  • The Clean Water Act (CWA) (33 U.S.C. 1251-1387) sets standards for the chemical, physical and biological properties of all bodies of water in the United States. It mandates a permitting system and is responsible for programs to mitigate the impacts of certain pollutants.
  • The Oil Pollution Act (OPA) (33 U.S.C. 2701) sets prevention, preparedness, and emergency response plan requirements to ensure environmental qualities.
  • The Safe Drinking Water Act (SDWA) (42 U.S.C. 300 et. seq.) protects public drinking water sources from unsafe pollutant levels by setting water quality standards. This act requires programs to ensure aquifer, reservoir, river, and lake health.

Office of Indian Energy and Economic Development-Laws Applicable to Geothermal Energy Development

Both primary and secondary water quality standards are mandated at the state and federal levels. Primary standards are strict requirements to mitigate public health effects. Secondary standards are strong recommendations, but are not required. These recommendations include cosmetic and aesthetic properties such as color, odor, and taste.

Water from geothermal sites are subsequently used as:

  • Drinking water to go onto a public water treatment plant
  • Untreated ground water and surface water
  • Treated effluent
  • Reclaimed or recycled water

These water sources are governed by state and federal regulations. Whether or not the injection water is potable, is decided on the state level. Potable water quality varies state to state, however, it is commonly referred to water that can be consumed by humans without posing any health risks.

Environmental Protection Agency-Aquifer Recharge and Aquifer Storage and Recovery

Water Quality Impacts & Mitigation

Geothermal plants ensure water quality standards are upheld because of the large quantities of water geothermal processes require and how many ecosystems effluent waters impact. Typical impacts and mitigation measures to ensure water quality are listed below.

Heating and Cooling Systems:

  • To mitigate impacts to lake and river species such as algae and fish, cooling towers, or air-cooled condensers, are used to reject waste heat into the atmosphere or nearby water sources. This process ensures that only small amounts of warm water are expelled into lakes and rivers.


  • Line injection wells with steel or titanium casing and cement to separate fluids from groundwater and other materials.
  • To mitigate casing and cement leaks; increase monitoring systems usage such as sonic logging instruments and videography.
  • Develop an operations and safety plan to mitigate blowouts, well casing failure, pipeline leakage, and other surface spills to decrease water contamination impacts.

Aquifer Contamination:

  • Primary and secondary drinking water standards may be difficult to meet when drilling additives or naturally occurring elements such as total dissolved solids, fluoride, chloride, and sulfate are either used or discovered to reduce solid deposition on equipment and casings.
  • When temperature increases, so does dissolved solid material. In the event of a leak in an EGS system, potential reservoir contamination increases. Hot-water contaminants include chlorides, silica, boron, and arsenic.
  • To mitigate contaminant levels, use disinfecting pathogens in the injection fluid. Remove soluble organic carbon before disinfecting to decrease the carbon reaction to form trihalomethanes and haloacetic acid in the reservoir. Side effects of disinfecting water prior to injection include situ residue. Since the quality of injection fluid varies state to state, contamination may be unavoidable where raw water and treated effluent water is allowed.
  • Arsenic and radionuclides may cause chemical differences between the injection solution and the receiving aquifer. Injection solutions that interact with the geologic matrix have higher reduction-oxidation components and may increase health risks.

Injection wells:

  • Geothermal drilling, testing, septic system, cesspools and wastewater wells are categorized by the Environmental Protection Agency (EPA) as Class V Underground Injection Control wells. These wells are shallow and use gravity to drain liquid waste into the ground. A state or federal agency may require permits and water quality tests. Some states require the well water to be potable to decrease the risk of aquifer contamination.

Factors Affecting Water Quality

To manage water quality, control the water quantity. Techniques to increase onsite water efficiency are listed below.

Onsite water efficiency:

  • Reuse water during construction for mud drilling and hydraulic stimulation fluids.
  • To decrease the overall water usage, reuse drilling fluids when drilling more than one well. Return geothermal fluids into the underground reservoir for proper disposal and to replenish the water supply.
  • When possible, use other water sources besides freshwater. These sources include, oil and gas production water, carbon capture and storage production water, and saline groundwater.
  • Use binary systems when possible. These systems mitigate water pollution by eliminating the non-condensable gas venting and decreasing the need for hydrogen sulfide controls. They minimize or eliminate many of the key drivers of scale formation. Binary systems also decrease the evaporative cooling losses that other geothermal resource extraction methods have.

Environmental Protection Agency-Aquifer Recharge and Aquifer Storage and Recovery