Geothermal Energy's Water Pollution: What's The Truth?

Geothermal energy is a renewable energy source that has the potential to affect the environment in various ways. While it is generally considered to have a positive impact by reducing the use of non-renewable energy sources, it does have some negative consequences. One of the key concerns is water contamination. Geothermal power plants require large amounts of water for cooling and re-injection, and the use of freshwater can impact water availability for other users and the environment. Additionally, the release of gases and fluids during the energy generation process can result in air pollution and water pollution if not properly contained and treated. The environmental impact of geothermal energy depends on the specific technology and cooling methods used, with closed-loop systems generally having fewer negative effects compared to open-loop systems.

Does Geothermal Energy Cause Pollution in Water?

Water contamination

Brine, a low-quality, high-temperature byproduct of geothermal processes, can contain dissolved compounds such as silica, sulfates, and carbonates. If brine were to mix with freshwater sources, it would degrade water quality. Additionally, scrubbers used to reduce air emissions in geothermal plants produce a watery sludge composed of captured materials, including sulfur, vanadium, silica compounds, chlorides, arsenic, mercury, nickel, and other heavy metals. This toxic sludge must be disposed of at hazardous waste sites, which can also contribute to water contamination if not properly managed.

The use of geothermal energy can have varying impacts on the local environment, depending on the technology used for conversion and cooling. Geothermal plants can require a large amount of water for cooling, and the use of freshwater for cooling can impact water availability and quality. However, most geothermal plants can use geothermal fluid instead of freshwater for cooling, reducing the overall water impact.

While water contamination is a potential issue, it is important to note that geothermal power plants emit significantly fewer harmful substances than fossil fuel power plants of similar sizes. Geothermal plants do not burn fuel to generate electricity, and closed-loop systems that directly convert geothermal steam or hot water into electricity generally have lower environmental impacts than open-loop systems that release waste into the atmosphere.

Air pollution

Geothermal energy is considered one of the cleanest forms of energy used for electricity generation today. However, it does have some impact on air quality.

Geothermal power plants emit small amounts of particulate matter and nitrous oxides, but these are negligible compared to other energy sources. The main air pollutant associated with geothermal energy is hydrogen sulfide, a corrosive and hazardous gas that can cause odour annoyances and, in high concentrations, lead to coma and death. Geothermal power plants can also release small amounts of carbon dioxide, methane, ammonia, and sulfur dioxide. These emissions are much lower than those of fossil fuel power plants, with lifecycle emissions of around 95% less than coal. Modern binary-cycle power plants recycle water and produce almost no air pollution.

To mitigate the release of hydrogen sulfide, geothermal power plants can install Hydrogen Sulfide Abatement Systems, which remove up to 99.9% of the gas before it is released into the atmosphere. Filtration systems can also be used to capture emissions, although the toxic sludge that results from this process must be carefully disposed of in a hazardous waste facility.

In addition to outdoor air pollution, geothermal activity can also cause indoor air pollution, particularly in buildings constructed on geothermal grounds. This can occur through the seepage of gases such as carbon dioxide, hydrogen sulfide, radon, and others through perforations in the structure.

Land subsidence

Geothermal power plants, particularly those using hydrothermal or enhanced geothermal systems, can contribute to land subsidence in several ways. Firstly, the extraction of large quantities of water from geothermal reservoirs can reduce the underlying support for the land above. Secondly, the reinjection of wastewater back into the reservoirs after capturing its heat can also influence land stability. While most geothermal facilities practice wastewater reinjection to prevent land subsidence, not all removed water is reinjected due to some being lost as steam. Consequently, outside water, including non-potable treated wastewater, is introduced to maintain reservoir levels, which can further impact land stability.

The risk of land subsidence is particularly relevant for hydrothermal plants, which are sited on geological "hot spots" with higher levels of earthquake risk. Enhanced geothermal systems, which involve drilling into the Earth's surface to access deeper geothermal resources, can also increase the likelihood of small earthquakes. These seismic activities induced by geothermal operations can trigger or exacerbate land subsidence.

To mitigate the risk of land subsidence, geothermal project developers must carefully consider the ecological sensitivity of the sites they select. Additionally, closed-loop systems, where gases are contained and reinjected into the ground, are preferred over open-loop systems to minimise air emissions and their potential contribution to land subsidence.

Noise pollution

The use of geothermal energy can impact the environment in several ways, including water contamination and the emission of harmful gases. However, the impact of geothermal power plants on water pollution is not commonly discussed. Instead, noise pollution is a more prevalent issue associated with geothermal energy extraction.

While most geothermal power plants are located away from populated areas, minimizing the impact of noise on residents, it is still a factor to consider when assessing the environmental impact of geothermal energy. Wind turbines, for example, often prompt more noise pollution complaints from residents than geothermal power plants. Nevertheless, it is essential to address and mitigate noise pollution to ensure the well-being of those living and working in close proximity to geothermal energy extraction sites.

To mitigate noise pollution, several measures can be implemented. These may include installing noise barriers or enclosures around noisy equipment, adopting noise control technologies, and carefully planning the layout and orientation of the plant to minimize the propagation of sound towards nearby residential areas. Regular maintenance of equipment can also help reduce unexpected failures or inefficient operations, which can contribute to excessive noise levels. Additionally, implementing noise monitoring systems can help detect and address noise level exceedances promptly.

Earthquake risk

The most widely developed type of geothermal power plant is hydrothermal plants, which are located near geological "hot spots" where molten rock close to the earth's crust produces hot water. Enhanced geothermal systems (hot dry rock) involve drilling into the Earth's surface to access deeper geothermal resources. These systems can increase the risk of small earthquakes.

The risk of earthquakes associated with enhanced geothermal systems can be reduced by situating plants at a safe distance from major fault lines. To control earthquake risk, drillers try to keep the size of fractures small and maintain steady water flow rates. The threshold goal for earthquakes is 2.0 or lower on the Richter scale.

In 2006, a magnitude 3.4 earthquake in Basel, Switzerland, led to the suspension of a geothermal project. The largest earthquake ever recorded while building an engineered geothermal system also occurred in Basel. Despite being minor, the quake rattled buildings and caused a loud sound that frightened residents.

In November 2017, a magnitude 5.5 earthquake shook Pohang, South Korea, injuring dozens and forcing more than 1,700 residents into emergency housing. Research attributed this earthquake to the development of a geothermal energy project. This event highlighted the potential for large earthquakes to occur due to geothermal projects.

Geothermal drilling can trigger earthquakes when drilled holes intersect with natural fractures, causing water to flash into steam and creating steam pressure that can generate electricity. Steam removal and water return can also cause earthquakes by producing new instability along fault or fracture lines.

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