Geothermal Water Quality
Present, Potentially Affected
- Antelope Valley Neset (AVS - Neset 345 kV Transmission Line Project)
- BLM-NV-WN-ES-08-01-1310, NV-020-08-01 (Blue Mountain Geothermal Well Field and Power Plant EA)
- Barren Ridge Renewable Transmission (Barren Ridge Renewable Transmission Project Environmental Impact Statement)
- Big Eddy-Knight (Big Eddy-Knight Transmission Project Environmental Impact Statement)
- Cameron to Milford-138kV Transmission Line (Cameron to Milford - 138kV Transmission Line Project)
- Central Ferry Lower Monumental (Central Ferry-Lower Monumental 500-kilovolt Transmission Line Project)
- DOI-BLM-ID-220-2009-EA-3709 (Raft River Geothermal Drilling Project EA for Geothermal/Exploration)
- DOI-BLM-NV-B020-2011-0026-EA (Clayton Valley Geothermal Exploration Project EA for Drilling and Well Testing)
- DOI-BLM-NV-B020-2012-0214-EA (Silver Peak Area Geothermal Exploration Project EA for Drilling and Well Testing for Geothermal/Exploration)
- DOI-BLM-OR-P000-2010-0003-EA (EA for Drilling, Testing and Monitoring of up to 12 Temperature Gradient / Passive Seismic Geothermal Exploratory Wells at Newberry Caldera Geothermal Area for Geothermal/Exploration)
- DOI-BLM-UT-W020-2010-042-EA (EA for Exploration and Development Drilling at Drum Mountain Geothermal Area for Geothermal/Exploration)
- Eldorado Ivanpah Transmission Project (EIS/EIR for the Eldorado-Ivanapah Transmission Project)
- Gateway West Transmission Line (Environmental Impact Statement for the Gateway West Transmission Line Project)
- McNary-John Day (McNary-John Day Transmission Line Project Environmental Impact Statement)
- Mona to Oquirrh Transmission (Mona to Oquirrh Transmission Corridor Project and Proposed Pony Express Resource Management Plan Amendment)
- North Steens 230kV Transmission (North Steens 230-kV Transmission Project EIS)
- One Nevada (Final Environmental Impact Statement for the One Nevada Transmission Line Project (ON Line Project))
- Sigurd Red Butte No2 (Sigurd to Red Butte No. 2 345kV Transmission Project)
- Southline Transmission Line (Environmental Impact Statement for the Southline Transmission Line Project)
- Sunzia Southwest (SunZia Southwest Transmission Project)
- Tehachapi Renewable Transmission (Environmental Impact Statement for the Tehachapi Renewable Transmission Project)
- Transwest Express (Transwest Express Transmission Project Environmental Impact Statement)
- Vantage Pomona Heights (Environmental Impact Statement for the Vanage to Pomona Heights 230kV Transmission Line Project)
- West-wide Energy Corridors (West-wide Energy Corridor Programmatic Environmental Impact Statement)
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.
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.
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.
- 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.
- 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.