Environmental impact of electricity generation

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Environmental_impact_of_electricity_generation

Greenhouse gas emissions per energy source.

Coal power is being phased out because of its pollution - such as Navajo Generating Station

Electric power systems consist of generation plants of different energy sources, transmission networks, and distribution lines. Each of these components can have environmental impacts at multiple stages of their development and use including in their construction, during the generation of electricity, and in their decommissioning and disposal. These impacts can be split into operational impacts (fuel sourcing, global atmospheric and localized pollution) and construction impacts (manufacturing, installation, decommissioning, and disposal). All forms of electricity generation have some form of environmental impact, but coal-fired power is the dirtiest. This page is organized by energy source and includes impacts such as water usage, emissions, local pollution, and wildlife displacement.

Greenhouse gas emissions

Greenhouse gas emissions are one of the environmental impacts of electricity generation. Measurement of life-cycle greenhouse gas emissions involves calculating the global warming potential (GWP) of energy sources through life-cycle assessment. These are usually sources of only electrical energy but sometimes sources of heat are evaluated. The findings are presented in units of global warming potential per unit of electrical energy generated by that source. The scale uses the global warming potential unit, the carbon dioxide equivalent (CO₂e), and the unit of electrical energy, the kilowatt hour (kWh). The goal of such assessments is to cover the full life of the source, from material and fuel mining through construction to operation and waste management.

In 2014, the Intergovernmental Panel on Climate Change harmonized the carbon dioxide equivalent (CO₂e) findings of the major electricity generating sources in use worldwide. This was done by analyzing the findings of hundreds of individual scientific papers assessing each energy source. Coal is by far the worst emitter, followed by natural gas, with solar, wind and nuclear all low-carbon. Hydropower, biomass, geothermal and ocean power may generally be low-carbon, but poor design or other factors could result in higher emissions from individual power stations.

For all technologies, advances in efficiency, and therefore reductions in CO₂e since the time of publication, have not been included. For example, the total life cycle emissions from wind power may have lessened since publication. Similarly, due to the time frame over which the studies were conducted, nuclear Generation II reactor's CO₂e results are presented and not the global warming potential of Generation III reactors. Other limitations of the data include: a) missing life cycle phases, and, b) uncertainty as to where to define the cut-off point in the global warming potential of an energy source. The latter is important in assessing a combined electrical grid in the real world, rather than the established practice of simply assessing the energy source in isolation.

Water usage

Water usage is one of the main environmental impacts of electricity generation. All thermal power plants (coal, natural gas, nuclear, geothermal, and biomass) use water as a cooling fluid to drive the thermodynamic cycles that allow electricity to be extracted from heat energy. Solar uses water for cleaning equipment, while hydroelectricity has water usage from evaporation from the reservoirs. The amount of water usage is often of great concern for electricity generating systems as populations increase and droughts become a concern. In addition, changes in water resources may impact the reliability of electricity generation.

Discussions of water usage of electricity generation distinguish between water withdrawal and water consumption. According to the United States Geological Survey, "withdrawal" is defined as the amount of water removed from the ground or diverted from a water source for use, while "consumption" refers to the amount of water that is evaporated, transpired, incorporated into products or crops, or otherwise removed from the immediate water environment. Both water withdrawal and consumption are important environmental impacts to evaluate.

General numbers for fresh water usage of different power sources are shown below.

	Water Consumption (gal/MW-h)
Power source	Low case	Medium/average case	High case
Nuclear power	100 (once-through cooling)	270 once-through, 650 (tower and pond)	845 (cooling tower)
Coal	58	500	1,100 (cooling tower, generic combustion)
Natural gas	100 (once-through cycle)	800 (steam-cycle, cooling towers)	1,170 (steam-cycle with cooling towers)
Hydroelectricity	1,430	4,491	18,000
Solar thermal	53 (dry cooling)	800	1,060 (Trough)
Geothermal	1,800		4,000
Biomass	300		480
Solar photovoltaic	0	26	33
Wind power	0	0	1

Steam-cycle plants (nuclear, coal, NG, solar thermal) require a great deal of water for cooling, to remove the heat at the steam condensers. The amount of water needed relative to plant output will be reduced with increasing boiler temperatures. Coal- and gas-fired boilers can produce high steam temperatures and so are more efficient, and require less cooling water relative to output. Nuclear boilers are limited in steam temperature by material constraints, and solar thermal is limited by concentration of the energy source.

Thermal cycle plants near the ocean have the option of using seawater. Such a site will not have cooling towers and will be much less limited by environmental concerns of the discharge temperature since dumping heat will have very little effect on water temperatures. This will also not deplete the water available for other uses. Nuclear power in Japan for instance, uses no cooling towers at all because all plants are located on the coast. If dry cooling systems are used, significant water from the water table will not be used. Other, more novel, cooling solutions exist, such as sewage cooling at the Palo Verde Nuclear Generating Station.

Hydroelectricity's main cause of water usage is both evaporation and seepage into the water table.

While water usage is still a major necessity for the production of electricity, since 2015 the use of water has decreased. In 2015 the total water withdrawals from thermoelectric power plants was just over 60 trillion gallons, but in 2020 it decreased to just under 50 trillion gallons. The water use has gone down because of the increase in the use of renewable energy sources.

80% of the decrease in water use is due to the use of natural gas and the use of renewables instead of just producing energy through coal-fired plants. And the other 20% of the decrease in water use comes from the implementation of closed loop recirculating and hybrid cooling systems rather than once through cooling systems. Once through cooling systems has an excessive amount of water withdrawals, so the water is only used once then released. While the closed loop water is reused several times so the water withdrawals is much lower.

Fossil fuels

See also: Environmental impact of the energy industry § Fossil fuel use, Environmental impact of the oil shale industry, and Health and environmental impact of the coal industry

Most electricity today is generated by burning fossil fuels and producing steam which is then used to drive a steam turbine that, in turn, drives an electrical generator.

More serious are concerns about the emissions that result from fossil fuel burning. Fossil fuels constitute a significant repository of carbon buried deep underground. Burning them results in the conversion of this carbon to carbon dioxide, which is then released into the atmosphere. The estimated CO₂ emission from the world's electrical power industry is 10 billion tonnes yearly. This results in an increase in the Earth's levels of atmospheric carbon dioxide, which enhances the greenhouse effect and contributes to global warming.

Coal power

Depending on the particular fossil fuel and the method of burning, other emissions may be produced as well. Ozone, sulfur dioxide, NO₂ and other gases are often released, as well as particulate matter. Sulfur and nitrogen oxides contribute to smog and acid rain. In the past, plant owners addressed this problem by building very tall flue-gas stacks, so that the pollutants would be diluted in the atmosphere. While this helps reduce local contamination, it does not help at all with global issues.

Fossil fuels, particularly coal, also contain dilute radioactive material, and burning them in very large quantities releases this material into the environment, leading to low levels of local and global radioactive contamination, the levels of which are, ironically, higher than a nuclear power station as their radioactive contaminants are controlled and stored.

Coal also contains traces of toxic heavy elements such as mercury, arsenic and others. Mercury vaporized in a power plant's boiler may stay suspended in the atmosphere and circulate around the world. While a substantial inventory of mercury exists in the environment, as other man-made emissions of mercury become better controlled, power plant emissions become a significant fraction of the remaining emissions. Power plant emissions of mercury in the United States are thought to be about 50 tons per year in 2003, and several hundred tons per year in China. Power plant designers can fit equipment to power stations to reduce emissions.

Coal mining practices in the United States have also included strip mining and removing mountain tops. Mill tailings are left out bare and have been leached into local rivers and resulted in most or all of the rivers in coal producing areas to run red year round with sulfuric acid that kills all life in the rivers.

Fossil gas power

In 2022 the IEA said that greenhouse gas emissions from gas-fired power plants had increased by nearly 3% the previous year and that more efforts were needed to reduce them.

As well as greenhouse gases, these power plants emit nitrogen oxides (NOx) but this is less dangerous than NOx from gas appliances in houses.

The efficiency of gas-fired power plants can be improved by co-generation and geothermal (combined heat and power) methods. Process steam can be extracted from steam turbines. Waste heat produced by thermal generating stations can be used for space heating of nearby buildings. By combining electric power production and heating, less fuel is consumed, thereby reducing the environmental effects compared with separate heat and power systems.

Fuel oil and diesel

Dirty oil is burnt in power plants in a few oil producing countries such as Iran. Diesel is often used in backup generators, which can cause air pollution.

Switching from fuels to electricity

Clean energy is mostly generated in the form of electricity, such as renewable energy or nuclear power. Switching to these energy sources requires that end uses, such as transport and heating, be electrified for the world's energy systems to be sustainable. In the U.S. and Canada the use of heat pumps (HP) can be economic if powered with solar photovoltaic (PV) devices to offset propane heating in rural areas and natural gas heating in cities. A 2023 study investigated: (1) a residential natural gas-based heating system and grid electricity, (2) a residential natural gas-based heating system with PV to serve the electric load, (3) a residential HP system with grid electricity, and (4) a residential HP+PV system. It found that under typical inflation conditions, the lifecycle cost of natural gas and reversible, air-source heat pumps are nearly identical, which in part explains why heat pump sales have surpassed gas furnace sales in the U.S. for the first time during a period of high inflation.

With higher rates of inflation or lower PV capital costs, PV becomes a hedge against rising prices and encourages the adoption of heat pumps by also locking in both electricity and heating cost growth. The study concludes: "The real internal rate of return for such prosumer technologies is 20x greater than a long-term certificate of deposit, which demonstrates the additional value PV and HP technologies offer prosumers over comparably secure investment vehicles while making substantive reductions in carbon emissions." This approach can be improved by integrating a thermal battery into the heat pump+solar energy heating system.

Nuclear power

See also: Nuclear power debate

Nuclear power activities involving the environment; mining, enrichment, generation and geological disposal.

Nuclear power has various environmental impacts, both positive and negative, including the construction and operation of the plant, the nuclear fuel cycle, and the effects of nuclear accidents. Nuclear power plants do not burn fossil fuels and so do not directly emit carbon dioxide. The carbon dioxide emitted during mining, enrichment, fabrication and transport of fuel is small when compared with the carbon dioxide emitted by fossil fuels of similar energy yield, however, these plants still produce other environmentally damaging wastes. Nuclear energy and renewable energy have reduced environmental costs by decreasing CO₂ emissions resulting from energy consumption.

There is a catastrophic risk potential if containment fails, which in nuclear reactors can be brought about by overheated fuels melting and releasing large quantities of fission products into the environment. In normal operation, nuclear power plants release less radioactive material than coal power plants whose fly ash contains significant amounts of thorium, uranium and their daughter nuclides.

A large nuclear power plant may reject waste heat to a natural body of water; this can result in undesirable increase of the water temperature with adverse effect on aquatic life. Alternatives include cooling towers.

Mining of uranium ore can disrupt the environment around the mine. However, with modern in-situ leaching technology this impact can be reduced compared to "classical" underground or open-pit mining. Disposal of spent nuclear fuel is controversial, with many proposed long-term storage schemes under intense review and criticism. Diversion of fresh- or low-burnup spent fuel to weapons production presents a risk of nuclear proliferation, however all nuclear weapons states derived the material for their first nuclear weapon from (non-power) research reactors or dedicated "production reactors" and/or uranium enrichment. Finally, some parts the structure of the reactor itself becomes radioactive through neutron activation and will require decades of storage before it can be economically dismantled and in turn disposed of as waste. Measures like reducing the cobalt content in steel to decrease the amount of cobalt-60 produced by neutron capture can reduce the amount of radioactive material produced and the radiotoxicity that originates from this material. However, part of the issue is not radiological but regulatory as most countries assume any given object that originates from the "hot" (radioactive) area of a nuclear power plant or a facility in the nuclear fuel cycle is ipso facto radioactive, even if no contamination or neutron irradiation induced radioactivity is detectable.

Renewable energy

Renewable power technologies can have significant environmental benefits. Unlike coal and natural gas, they can generate electricity and fuels without releasing significant quantities of CO₂ and other greenhouse gases that contribute to climate change, however the greenhouse gas savings from a number of biofuels have been found to be much less than originally anticipated, as discussed in the article Indirect land use change impacts of biofuels.

Both solar and wind have been criticized from an aesthetic point of view. However, methods and opportunities exist to deploy these renewable technologies efficiently and unobtrusively: fixed solar collectors can double as noise barriers along highways, and extensive roadway, parking lot, and roof-top area is currently available; amorphous photovoltaic cells can also be used to tint windows and produce energy.

Hydroelectricity

See also: Environmental impact of reservoirs and Hydroelectricity § Advantages and disadvantages

The major advantage of conventional hydroelectric dams with reservoirs is their ability to store potential power for later electrical production. The combination of a natural supply of energy and production on demand has made hydro power the largest source of renewable energy by far. Other advantages include longer life than fuel-fired generation, low operating costs, and the provision of facilities for water sports. Some dams also operate as pumped-storage plants balancing supply and demand in the generation system. Overall, hydroelectric power can be less expensive than electricity generated from fossil fuels or nuclear energy, and areas with abundant hydroelectric power attract industry.

However, in addition to the advantages above, there are several disadvantages to dams that create large reservoirs. These may include: dislocation of people living where the reservoirs are planned, release of significant amounts of carbon dioxide at construction and flooding of the reservoir, disruption of aquatic ecosystems and bird life, adverse impacts on the river environment, and in rare cases catastrophic failure of the dam wall.

Some other disadvantages of the construction of hydroelectric dams is having to build access roads to get to the dam which disrupt the land ecosystem and not just the water ecosystems. Also with the increase in carbon dioxide, there is an increase in methane. This is from the flooding during the creation of the dams, when plants are submerged underwater and decay, they release methane gas. Another disadvantage is the upfront cost to build the dam and the amount of time it takes to build it.

Some dams only generate power and serve no other purpose, but in many places large reservoirs are needed for flood control and/or irrigation, adding a hydroelectric portion is a common way to pay for a new reservoir. Flood control protects life/property and irrigation supports increased agriculture.

Small hydro and run-of-the-river are two low impact alternatives to hydroelectric reservoirs, although they may produce intermittent power due to a lack of stored water.

Tidal

Tidal power can affect marine life. The turbines' rotating blades can accidentally kill swimming sea life. Projects such as the one in Strangford include a safety mechanism that turns off the turbine when marine animals approach. However, this feature causes a major loss in energy because of the amount of marine life that passes through the turbines. Some fish may avoid the area if threatened by a constantly rotating or noisy object. Marine life is a huge factor when siting tidal power energy generators, and precautions are taken to ensure that as few marine animals as possible are affected by it. In terms of global warming potential (i.e. carbon footprint), the impact of tidal power generation technologies ranges between 15 and 37 gCO₂-eq/kWhe, with a median value of 23.8 gCO₂-eq/kWhe. This is in line with the impact of other renewables like wind and solar power, and significantly better than fossil-based technologies. The Tethys database provides access to scientific literature and general information on the potential environmental effects of tidal energy.

Biomass

Further information: Biomass § Environmental impact

Electrical power can be generated by burning anything which will combust. Some electrical power is generated by burning crops which are grown specifically for the purpose. Usually this is done by fermenting plant matter to produce ethanol, which is then burned. This may also be done by allowing organic matter to decay, producing biogas, which is then burned. Also, when burned, wood is a form of biomass fuel.

Burning biomass produces many of the same emissions as burning fossil fuels. However, growing biomass captures carbon dioxide out of the air, so that the net contribution to global atmospheric carbon dioxide levels is small.

The process of growing biomass is subject to the same environmental concerns as any kind of agriculture. It uses a large amount of land, and fertilizers and pesticides may be necessary for cost-effective growth. Biomass that is produced as a by-product of agriculture shows some promise, but most such biomass is currently being used, for plowing back into the soil as fertilizer if nothing else.

Wind power

Livestock grazing near a wind turbine

The environmental impact of electricity generation from wind power is minor when compared to that of fossil fuel power. Wind power consumes no fuel, and emits no air pollution, unlike fossil fuels. Wind turbines have some of the lowest global warming potential per unit of electricity generated: far less greenhouse gas is emitted than for the average unit of electricity, so wind power helps limit climate change. Emissions from production of a turbine are recouped in less than a year of operation, as it replaces gas or coal power.

Onshore (on-land) wind farms can have a significant visual impact and impact on the landscape. Due to a very low surface power density and spacing requirements, wind farms typically need to be spread over more land than other power stations. Conflicts arise especially in scenic and culturally-important landscapes. Siting restrictions, such as setbacks,may be implemented to limit the impact. The land between the turbines and access roads can still be used for farming and grazing. Some wind farms are opposed for potentially spoiling protected scenic areas, archaeological landscapes and heritage sites.

Habitat loss and fragmentation are the greatest potential impacts on wildlife of onshore wind farms, but they are small and can be mitigated if proper monitoring and mitigation strategies are implemented. The worldwide ecological impact is minimal. Thousands of birds and bats, including rare species, have been killed by wind turbine blades, as around other manmade structures, though wind turbines are responsible for far fewer bird deaths than fossil-fuel infrastructure. This can be mitigated with proper wildlife monitoring.

Many wind turbine blades are made of fiberglass and some only had a lifetime of 10 to 20 years. Previously, there was no market for recycling these old blades, and they were commonly disposed of in landfills. Because blades are hollow, they take up a large volume compared to their mass. Since 2019, some landfill operators have begun requiring blades to be crushed before being landfilled. Blades manufactured in the 2020s are more likely to be designed to be completely recyclable.

Wind turbines also generate noise. At a distance of 300 metres (980 ft) this may be around 45 dB, which is slightly louder than a refrigerator. At 1.5 km (1 mi) distance they become inaudible. Some people who live very close to wind turbines have reported negative health effects, but peer-reviewed research has generally not supported these claims. Pile-driving to construct non-floating wind farms is noisy underwater, but in operation offshore wind is much quieter than ships.

Geothermal power

Main article: Geothermal power

Geothermal energy is the heat of the Earth, which can be tapped into to produce electricity in power plants. Warm water produced from geothermal sources can be used for industry, agriculture, bathing and cleansing. Where underground steam sources can be tapped, the steam is used to run a steam turbine. Geothermal steam sources have a finite life as underground water is depleted. Arrangements that circulate surface water through rock formations to produce hot water or steam are, on a human-relevant time scale, renewable.

While a geothermal power plant does not burn any fuel, it will still have emissions due to substances other than steam which come up from the geothermal wells. These may include hydrogen sulfide, and carbon dioxide. Some geothermal steam sources entrain non-soluble minerals that must be removed from the steam before it is used for generation; this material must be properly disposed. Any (closed cycle) steam power plant requires cooling water for condensers; diversion of cooling water from natural sources, and its increased temperature when returned to streams or lakes, may have a significant impact on local ecosystems.

Removal of ground water and accelerated cooling of rock formations can cause earth tremors. Enhanced geothermal systems (EGS) fracture underground rock to produce more steam; such projects can cause earthquakes. Certain geothermal projects (such as one near Basel, Switzerland in 2006) have been suspended or canceled owing to objectionable seismicity induced by geothermal recovery. However, risks associated with "hydrofracturing induced seismicity are low compared to that of natural earthquakes, and can be reduced by careful management and monitoring" and "should not be regarded as an impediment to further development of the Hot Rock geothermal energy resource".

Solar power

This section is an excerpt from Solar power § Environmental effects.[edit]

Part of the Senftenberg Solarpark, a solar photovoltaic power plant located on former open-pit mining areas close to the city of Senftenberg, in Eastern Germany. The 78 MW Phase 1 of the plant was completed within three months.

Solar power is cleaner than electricity from fossil fuels, and is better for the environment than burning things. Solar power does not lead to harmful emissions during operation, but the production of the panels creates some pollution. The carbon footprint of manufacturing is less than 1kg CO₂/Wp, and this is expected to fall as manufacturers use more clean electricity and recycled materials. Solar power carries an upfront cost to the environment via production with a carbon payback time of several years as of 2022, but offers clean energy for the remainder of their 30-year lifetime.

The life-cycle greenhouse-gas emissions of solar farms are less than 50 gram (g) per kilowatt-hour (kWh), but with battery storage could be up to 150 g/kWh. In contrast, a combined cycle gas-fired power plant without carbon capture and storage emits around 500 g/kWh, and a coal-fired power plant about 1000 g/kWh. Similar to all energy sources where their total life cycle emissions are mostly from construction, the switch to low carbon power in the manufacturing and transportation of solar devices would further reduce carbon emissions.

Lifecycle surface power density of solar power varies but averages about 7 W/m2, compared to about 240 for nuclear power and 480 for gas. However, when the land required for gas extraction and processing is accounted for, gas power is estimated to have not much higher power density than solar. According to a 2021 study, obtaining 25% to 80% of electricity from solar farms in their own territory by 2050 would require the panels to cover land ranging from 0.5% to 2.8% of the European Union, 0.3% to 1.4% in India, and 1.2% to 5.2% in Japan and South Korea. Occupation of such large areas for PV farms could drive residential opposition as well as lead to deforestation, removal of vegetation and conversion of farm land. However some countries, such as South Korea and Japan, use land for agriculture under PV or floating solar, together with other low-carbon power sources. Worldwide land use has minimal ecological impact. Land use can be reduced to the level of gas power by installing on buildings and other built up areas.

Harmful materials are used in the production of solar panels, but generally in small amounts. As of 2022, the environmental impact of perovskite is difficult to estimate, but there is some concern that lead may be a problem.

A 2021 International Energy Agency study projects the demand for copper will double by 2040. The study cautions that supply needs to increase rapidly to match demand from large-scale deployment of solar and required grid upgrades. More tellurium and indium may also be needed.

Recycling may help. As solar panels are sometimes replaced with more efficient panels, the second-hand panels are sometimes reused in developing countries, for example in Africa. Several countries have specific regulations for the recycling of solar panels. Although maintenance cost is already low compared to other energy sources, some academics have called for solar power systems to be designed to be more repairable.

Solar panels can increase local temperature. In large installation in the desert, the effect can be stronger than the urban heat island.

A very small proportion of solar power is concentrated solar power. Concentrated solar power may use much more water than gas-fired power. This can be a problem, as this type of solar power needs strong sunlight so is often built in deserts.

Environmental impact of fracking

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Environmental_impact_of_fracking 

Shale gas drilling rig near Alvarado, Texas

The environmental impact of fracking is related to land use and water consumption, air emissions, including methane emissions, brine and fracturing fluid leakage, water contamination, noise pollution, and health. Water and air pollution are the biggest risks to human health from fracking. Research has determined that fracking negatively affects human health and drives climate change.

Fracking fluids include proppants and other substances, which include chemicals known to be toxic, as well as unknown chemicals that may be toxic. In the United States, such additives may be treated as trade secrets by companies who use them. Lack of knowledge about specific chemicals has complicated efforts to develop risk management policies and to study health effects. In other jurisdictions, such as the United Kingdom, these chemicals must be made public and their applications are required to be nonhazardous.

Water usage by fracking can be a problem in areas that experience water shortage. Surface water may be contaminated through spillage and improperly built and maintained waste pits, in jurisdictions where these are permitted. Further, ground water can be contaminated if fracturing fluids and formation fluids are able to escape during fracking. However, the possibility of groundwater contamination from the fracturing fluid upward migration is negligible, even in a long-term period. Produced water, the water that returns to the surface after fracking, is managed by underground injection, municipal and commercial wastewater treatment, and reuse in future wells. There is potential for methane to leak into ground water and the air, though escape of methane is a bigger problem in older wells than in those built under more recent legislation.

Fracking causes induced seismicity called microseismic events or microearthquakes. The magnitude of these events is too small to be detected at the surface, being of magnitude M-3 to M-1 usually. However, fluid disposal wells (which are often used in the USA to dispose of polluted waste from several industries) have been responsible for earthquakes up to 5.6M in Oklahoma and other states.

Governments worldwide are developing regulatory frameworks to assess and manage environmental and associated health risks, working under pressure from industry on the one hand, and from anti-fracking groups on the other. In some countries like France a precautionary approach has been favored and fracking has been banned. The United Kingdom's regulatory framework is based on the conclusion that the risks associated with fracking are manageable if carried out under effective regulation and if operational best practices are implemented. It has been suggested by the authors of meta-studies that in order to avoid further negative impacts, greater adherence to regulation and safety procedures are necessary.

Air emissions

A report for the European Union on the potential risks was produced in 2012. Potential risks are "methane emissions from the wells, diesel fumes and other hazardous pollutants, ozone precursors or odours from hydraulic fracturing equipment, such as compressors, pumps, and valves". Also gases and hydraulic fracturing fluids dissolved in flowback water pose air emissions risks. One study measured various air pollutants weekly for a year surrounding the development of a newly fractured gas well and detected nonmethane hydrocarbons, methylene chloride (a toxic solvent), and polycyclic aromatic hydrocarbons. These pollutants have been shown to affect fetal outcomes.

The relationship between hydraulic fracturing and air quality can influence acute and chronic respiratory illnesses, including exacerbation of asthma (induced by airborne particulates, ozone and exhaust from equipment used for drilling and transport) and COPD. For example, communities overlying the Marcellus shale have higher frequencies of asthma. Children, active young adults who spend time outdoors, and the elderly are particularly vulnerable. OSHA has also raised concerns about the long-term respiratory effects of occupational exposure to airborne silica at hydraulic fracturing sites. Silicosis can be associated with systemic autoimmune processes.

"In the UK, all oil and gas operators must minimise the release of gases as a condition of their licence from the Department of Energy and Climate Change (DECC). Natural gas may only be vented for safety reasons."

Also transportation of necessary water volume for hydraulic fracturing, if done by trucks, can cause emissions. Piped water supplies can reduce the number of truck movements necessary.

A report from the Pennsylvania Department of Environmental Protection indicated that there is little potential for radiation exposure from oil and gas operations.

Air pollution is of particular concern to workers at hydraulic fracturing well sites as the chemical emissions from storage tanks and open flowback pits combine with the geographically compounded air concentrations from surrounding wells. Thirty seven percent of the chemicals used in hydraulic fracturing operations are volatile and can become airborne.

Researchers Chen and Carter from the Department of Civil and Environmental Engineering, University of Tennessee, Knoxville used atmospheric dispersion models (AERMOD) to estimate the potential exposure concentration of emissions for calculated radial distances of 5 m to 180m from emission sources. The team examined emissions from 60,644 hydraulic fracturing wells and found "results showed the percentage of wells and their potential acute non-cancer, chronic non-cancer, acute cancer, and chronic cancer risks for exposure to workers were 12.41%, 0.11%, 7.53%, and 5.80%, respectively. Acute and chronic cancer risks were dominated by emissions from the chemical storage tanks within a 20 m radius.

Climate change

Hydraulic fracturing is a driver of climate change. However, whether natural gas produced by hydraulic fracturing causes higher well-to-burner emissions than gas produced from conventional wells is a matter of contention. Some studies have found that hydraulic fracturing has higher emissions due to methane released during completing wells as some gas returns to the surface, together with the fracturing fluids. Depending on their treatment, the well-to-burner emissions are 3.5%–12% higher than for conventional gas.

A debate has arisen particularly around a study by professor Robert W. Howarth finding shale gas significantly worse for global warming than oil or coal. Other researchers have criticized Howarth's analysis, including Cathles et al., whose estimates were substantially lower." A 2012 industry funded report co-authored by researchers at the United States Department of Energy's National Renewable Energy Laboratory found emissions from shale gas, when burned for electricity, were "very similar" to those from so-called "conventional well" natural gas, and less than half the emissions of coal.

Studies which have estimated lifecycle methane leakage from natural gas development and production have found a wide range of leakage rates. According to the Environmental Protection Agency's Greenhouse Gas Inventory, the methane leakage rate is about 1.4%. A 16-part assessment of methane leakage from natural gas production initiated by the Environmental Defense Fund found that fugitive emissions in key stages of the natural gas production process are significantly higher than estimates in the EPA's national emission inventory, with a leakage rate of 2.3 percent of overall natural gas output.

Water consumption

Massive hydraulic fracturing typical of shale wells uses between 1.2 and 3.5 million US gallons (4,500 and 13,200 m³) of water per well, with large projects using up to 5 million US gallons (19,000 m³). Additional water is used when wells are refractured. An average well requires 3 to 8 million US gallons (11,000 to 30,000 m³) of water over its lifetime. According to the Oxford Institute for Energy Studies, greater volumes of fracturing fluids are required in Europe, where the shale depths average 1.5 times greater than in the U.S. Whilst the published amounts may seem large, they are small in comparison with the overall water usage in most areas. A study in Texas, which is a water shortage area, indicates "Water use for shale gas is <1% of statewide water withdrawals; however, local impacts vary with water availability and competing demands."

A report by the Royal Society and the Royal Academy of Engineering shows the usage expected for hydraulic fracturing a well is approximately the amount needed to run a 1,000 MW coal-fired power plant for 12 hours. A 2011 report from the Tyndall Centre estimates that to support a 9 billion cubic metres per annum (320×10⁹ cu ft/a) gas production industry, between 1.25 to 1.65 million cubic metres (44×10⁶ to 58×10⁶ cu ft) would be needed annually, which amounts to 0.01% of the total water abstraction nationally.

Concern has been raised over the increasing quantities of water for hydraulic fracturing in areas that experience water stress. Use of water for hydraulic fracturing can divert water from stream flow, water supplies for municipalities and industries such as power generation, as well as recreation and aquatic life.^[48] The large volumes of water required for most common hydraulic fracturing methods have raised concerns for arid regions, such as the Karoo in South Africa, and in drought-prone Texas, in North America.^[50] It may also require water overland piping from distant sources.

A 2014 life cycle analysis of natural gas electricity by the National Renewable Energy Laboratory concluded that electricity generated by natural gas from massive hydraulically fractured wells consumed between 249 gallons per megawatt-hour (gal/MWhr) (Marcellus trend) and 272 gal/MWhr (Barnett Shale). The water consumption for the gas from massive hydraulic fractured wells was from 52 to 75 gal/MWhr greater (26 percent to 38 percent greater) than the 197 gal/MWhr consumed for electricity from conventional onshore natural gas.

Some producers have developed hydraulic fracturing techniques that could reduce the need for water. Using carbon dioxide, liquid propane or other gases instead of water have been proposed to reduce water consumption. After it is used, the propane returns to its gaseous state and can be collected and reused. In addition to water savings, gas fracturing reportedly produces less damage to rock formations that can impede production. Recycled flowback water can be reused in hydraulic fracturing. It lowers the total amount of water used and reduces the need to dispose of wastewater after use. The technique is relatively expensive, however, since the water must be treated before each reuse and it can shorten the life of some types of equipment.

Water contamination

Injected fluid

In the United States, hydraulic fracturing fluids include proppants, radionuclide tracers, and other chemicals, many of which are toxic. The type of chemicals used in hydraulic fracturing and their properties vary. While most of them are common and generally harmless, some chemicals are carcinogenic. Out of 2,500 products used as hydraulic fracturing additives in the United States, 652 contained one or more of 29 chemical compounds which are either known or possible human carcinogens, regulated under the Safe Drinking Water Act for their risks to human health, or listed as hazardous air pollutants under the Clean Air Act. Another 2011 study identified 632 chemicals used in United States natural gas operations, of which only 353 are well-described in the scientific literature. A study that assessed health effects of chemicals used in fracturing found that 73% of the products had between 6 and 14 different adverse health effects including skin, eye, and sensory organ damage; respiratory distress including asthma; gastrointestinal and liver disease; brain and nervous system harms; cancers; and negative reproductive effects.

An expansive study conducted by the Yale School of Public Health in 2016 found numerous chemicals involved in or released by hydraulic fracturing are carcinogenic. Of the 119 compounds identified in this study with sufficient data, "44% of the water pollutants...were either confirmed or possible carcinogens." However, the majority of chemicals lacked sufficient data on carcinogenic potential, highlighting the knowledge gap in this area. Further research is needed to identify both carcinogenic potential of chemicals used in hydraulic fracturing and their cancer risk.

The European Union regulatory regime requires full disclosure of all additives. According to the EU groundwater directive of 2006, "in order to protect the environment as a whole, and human health in particular, detrimental concentrations of harmful pollutants in groundwater must be avoided, prevented or reduced." In the United Kingdom, only chemicals that are "non hazardous in their application" are licensed by the Environment Agency.

Flowback

Less than half of injected water is recovered as flowback or later production brine, and in many cases recovery is <30%. As the fracturing fluid flows back through the well, it consists of spent fluids and may contain dissolved constituents such as minerals and brine waters. In some cases, depending on the geology of the formation, it may contain uranium, radium, radon and thorium. Estimates of the amount of injected fluid returning to the surface range from 15-20% to 30–70%.

Approaches to managing these fluids, commonly known as produced water, include underground injection, municipal and commercial wastewater treatment and discharge, self-contained systems at well sites or fields, and recycling to fracture future wells. The vacuum multi-effect membrane distillation system as a more effective treatment system has been proposed for treatment of flowback. However, the quantity of waste water needing treatment and the improper configuration of sewage plants have become an issue in some regions of the United States. Part of the wastewater from hydraulic fracturing operations is processed there by public sewage treatment plants, which are not equipped to remove radioactive material and are not required to test for it.

Produced water spills and subsequent contamination of groundwater also presents a risk for exposure to carcinogens. Research that modeled the solute transport of BTEX (benzene, toluene, ethylbenzene, and xylene) and naphthalene for a range of spill sizes on contrasting soils overlying groundwater at different depths found that benzene and toluene were expected to reach human health relevant concentration in groundwater because of their high concentrations in produced water, relatively low solid/liquid partition coefficient and low EPA drinking water limits for these contaminants. Benzene is a known carcinogen which affects the central nervous system in the short term and can affect the bone marrow, blood production, immune system, and urogenital systems with long term exposure.

Surface spills

Surface spills related to the hydraulic fracturing occur mainly because of equipment failure or engineering misjudgments.

Volatile chemicals held in waste water evaporation ponds can evaporate into the atmosphere, or overflow. The runoff can also end up in groundwater systems. Groundwater may become contaminated by trucks carrying hydraulic fracturing chemicals and wastewater if they are involved in accidents on the way to hydraulic fracturing sites or disposal destinations.

In the evolving European Union legislation, it is required that "Member States should ensure that the installation is constructed in a way that prevents possible surface leaks and spills to soil, water or air." Evaporation and open ponds are not permitted. Regulations call for all pollution pathways to be identified and mitigated. The use of chemical proof drilling pads to contain chemical spills is required. In the UK, total gas security is required, and venting of methane is only permitted in an emergency.

Methane

In September 2014, a study from the US Proceedings of the National Academy of Sciences released a report that indicated that methane contamination can be correlated to distance from a well in wells that were known to leak. This however was not caused by the hydraulic fracturing process, but by poor cementation of casings.

Groundwater methane contamination has adverse effect on water quality and in extreme cases may lead to potential explosion. A scientific study conducted by researchers of Duke University found high correlations of gas well drilling activities, including hydraulic fracturing, and methane pollution of the drinking water. According to the 2011 study of the MIT Energy Initiative, "there is evidence of natural gas (methane) migration into freshwater zones in some areas, most likely as a result of substandard well completion practices i.e. poor quality cementing job or bad casing, by a few operators." A 2013 Duke study suggested that either faulty construction (defective cement seals in the upper part of wells, and faulty steel linings within deeper layers) combined with a peculiarity of local geology may be allowing methane to seep into waters; the latter cause may also release injected fluids to the aquifer. Abandoned gas and oil wells also provide conduits to the surface in areas like Pennsylvania, where these are common.

A study by Cabot Oil and Gas examined the Duke study using a larger sample size, found that methane concentrations were related to topography, with the highest readings found in low-lying areas, rather than related to distance from gas production areas. Using a more precise isotopic analysis, they showed that the methane found in the water wells came from both the formations where hydraulic fracturing occurred, and from the shallower formations. The Colorado Oil & Gas Conservation Commission investigates complaints from water well owners, and has found some wells to contain biogenic methane unrelated to oil and gas wells, but others that have thermogenic methane due to oil and gas wells with leaking well casing. A review published in February 2012 found no direct evidence that hydraulic fracturing actual injection phase resulted in contamination of ground water, and suggests that reported problems occur due to leaks in its fluid or waste storage apparatus; the review says that methane in water wells in some areas probably comes from natural resources.

Another 2013 review found that hydraulic fracturing technologies are not free from risk of contaminating groundwater, and described the controversy over whether the methane that has been detected in private groundwater wells near hydraulic fracturing sites has been caused by drilling or by natural processes.

Radionuclides

Main article: Naturally occurring radioactive material

There are naturally occurring radioactive materials (NORM), for example radium, radon, uranium, and thorium, in shale deposits. Brine co-produced and brought to the surface along with the oil and gas sometimes contains naturally occurring radioactive materials; brine from many shale gas wells, contains these radioactive materials. The U.S. Environmental Protection Agency and regulators in North Dakota consider radioactive material in flowback a potential hazard to workers at hydraulic fracturing drilling and waste disposal sites and those living or working nearby if the correct procedures are not followed. A report from the Pennsylvania Department of Environmental Protection indicated that there is little potential for radiation exposure from oil and gas operations.

Land use

In the UK, the likely well spacing visualised by the December 2013 DECC Strategic Environmental Assessment report indicated that well pad spacings of 5 km were likely in crowded areas, with up to 3 hectares (7.4 acres) per well pad. Each pad could have 24 separate wells. This amounts to 0.16% of land area. A study published in 2015 on the Fayetteville Shale found that a mature gas field impacted about 2% of the land area and substantially increased edge habitat creation. Average land impact per well was 3 hectares (about 7 acres)  In another case study for a watershed in Ohio, lands disturbed over 20 years amount to 9.7% of the watershed area, with only 0.24% attributed to fracking wellpad construction. Research indicates that effects on ecosystem services costs (i.e. those processes that the natural world provides to humanity) has reached over $250 million per year in the U.S.

Seismicity

Hydraulic fracturing causes induced seismicity called microseismic events or microearthquakes. These microseismic events are often used to map the horizontal and vertical extent of the fracturing. The magnitude of these events is usually too small to be detected at the surface, although the biggest micro-earthquakes may have the magnitude of about -1.5 (M_w).

Induced seismicity from hydraulic fracturing

As of August 2016, there were at least nine known cases of fault reactivation by hydraulic fracturing that caused induced seismicity strong enough to be felt by humans at the surface: In Canada, there have been three in Alberta (M 4.8 and M 4.4 and M 4.4) and three in British Columbia (M 4.6, M 4.4 and M 3.8); In the United States there has been: one in Oklahoma (M 2.8) and one in Ohio (M 3.0), and; In the United Kingdom, there have been two in Lancashire (M 2.3 and M 1.5).

Induced seismicity from water disposal wells

According to the USGS only a small fraction of roughly 30,000 waste fluid disposal wells for oil and gas operations in the United States have induced earthquakes that are large enough to be of concern to the public. Although the magnitudes of these quakes has been small, the USGS says that there is no guarantee that larger quakes will not occur. In addition, the frequency of the quakes has been increasing. In 2009, there were 50 earthquakes greater than magnitude 3.0 in the area spanning Alabama and Montana, and there were 87 quakes in 2010. In 2011 there were 134 earthquakes in the same area, a sixfold increase over 20th century levels. There are also concerns that quakes may damage underground gas, oil, and water lines and wells that were not designed to withstand earthquakes.

A 2012 US Geological Survey study reported that a "remarkable" increase in the rate of M ≥ 3 earthquakes in the US midcontinent "is currently in progress", having started in 2001 and culminating in a 6-fold increase over 20th century levels in 2011. The overall increase was tied to earthquake increases in a few specific areas: the Raton Basin of southern Colorado (site of coalbed methane activity), and gas-producing areas in central and southern Oklahoma, and central Arkansas. While analysis suggested that the increase is "almost certainly man-made", the USGS noted: "USGS's studies suggest that the actual hydraulic fracturing process is only very rarely the direct cause of felt earthquakes." The increased earthquakes were said to be most likely caused by increased injection of gas-well wastewater into disposal wells. The injection of waste water from oil and gas operations, including from hydraulic fracturing, into saltwater disposal wells may cause bigger low-magnitude tremors, being registered up to 3.3 (M_w).

Noise

Each well pad (in average 10 wells per pad) needs during preparatory and hydraulic fracturing process about 800 to 2,500 days of activity, which may affect residents. In addition, noise is created by transport related to the hydraulic fracturing activities. Noise pollution from hydraulic fracturing operations (e.g., traffic, flares/burn-offs) is often cited as a source of psychological distress, as well as poor academic performance in children. For example, the low-frequency noise that comes from well pumps contributes to irritation, unease, and fatigue.

The UK Onshore Oil and Gas (UKOOG) is the industry representative body, and it has published a charter that shows how noise concerns will be mitigated, using sound insulation, and heavily silenced rigs where this is needed.

Safety issues

In July 2013, the United States Federal Railroad Administration listed oil contamination by hydraulic fracturing chemicals as "a possible cause" of corrosion in oil tank cars.

Community impacts

Impacted communities are often already vulnerable, including poor, rural, or indigenous persons, who may continue to experience the deleterious effects of hydraulic fracturing for generations. Facility siting in fracking projects disproportionately tilts towards lower income communities, a persisting issue partially due to these disadvantaged residents not having the resources to evade environmental hazards. A spatial analysis of the demographics of residents around fracking sites found that median incomes around wells in Pennsylvania were substantially lower. Competition for resources between farmers and oil companies contributes to stress for agricultural workers and their families, as well as to a community-level "us versus them" mentality that creates community distress. Rural communities that host hydraulic fracturing operations often experience a "boom/bust cycle," whereby their population surges, consequently exerting stress on community infrastructure and service provision capabilities (e.g., medical care, law enforcement). A study of rural communities around fracking sites in Pennsylvania found that while there was some local support of fracking as a source of jobs and a boost to small businesses, there was more skepticism of if these jobs would stay within the community at all, and if there would be a significant 'bust' to the economy after the natural gas dried up.

Indigenous and agricultural communities may be particularly impacted by hydraulic fracturing, given their historical attachment to, and dependency on, the land they live on, which is often damaged as a result of the hydraulic fracturing process. Native Americans are especially vulnerable to the negative environmental impacts of fracking operations, in part due to existing legislature surrounding fracking wastewater and environmental pollutants on indigenous lands. The Resource Conservation and Recovery Act (RCRA) has a special exemption preventing indigenous groups from protecting their water sources with quality standards. Native Americans, particularly those living on rural reservations, may be particularly vulnerable to the effects of fracturing; that is, on the one hand, tribes may be tempted to engage with the oil companies to secure a source of income but, on the other hand, must often engage in legal battles to protect their sovereign rights and the natural resources of their land.

While hydraulic fracturing is primarily recognized for its impacts on the natural environment, it also can provide stressors on a community's mental state. Research suggests that the activity surrounding fracking operations leads to a degree of degradation in 'socio-psychological functioning' of surrounding community members. In an attempt to support findings from the existing literature, one study performed a series of interviews with residents of Denton, Texas to get a community's personalized testimony. These discussions found that residents experienced heightened stress, anxiety, and hopelessness, as well as feeling a 'lack of control' over their community. Researchers also uncovered polarizing attitudes, a communal rift forming between those with pro and anti fracking beliefs.

Policy and science

Main article: Regulation of hydraulic fracturing

There are two main approaches to regulation that derive from policy debates about how to manage risk and a corresponding debate about how to assess risk.

The two main schools of regulation are science-based assessment of risk and the taking of measures to prevent harm from those risks through an approach like hazard analysis, and the precautionary principle, where action is taken before risks are well-identified. The relevance and reliability of risk assessments in communities where hydraulic fracturing occurs has also been debated amongst environmental groups, health scientists, and industry leaders. The risks, to some, are overplayed and the current research is insufficient in showing the link between hydraulic fracturing and adverse health effects, while to others the risks are obvious and risk assessment is underfunded.

Different regulatory approaches have thus emerged. In France and Vermont for instance, a precautionary approach has been favored and hydraulic fracturing has been banned based on two principles: the precautionary principle and the prevention principle. Nevertheless, some States such as the U.S. have adopted a risk assessment approach, which had led to many regulatory debates over the issue of hydraulic fracturing and its risks.

In the UK, the regulatory framework is largely being shaped by a report commissioned by the UK Government in 2012, whose purpose was to identify the problems around hydraulic fracturing and to advise the country's regulatory agencies. Jointly published by the Royal Society and the Royal Academy of Engineering, under the chairmanship of Professor Robert Mair, the report features ten recommendations covering issues such as groundwater contamination, well integrity, seismic risk, gas leakages, water management, environmental risks, best practice for risk management, and also includes advice for regulators and research councils. The report was notable for stating that the risks associated with hydraulic fracturing are manageable if carried out under effective regulation and if operational best practices are implemented.

A 2013 review concluded that, in the US, confidentiality requirements dictated by legal investigations have impeded peer-reviewed research into environmental impacts.

When looking at the regulations of fracking from the perspective of land rights, historic and continuing injustices against Native Americans are one angle to consider. Some legislature, such as the National Environmental Policy Act (NEPA), is written in a way that it only protects indigenous 'cultural resources' on specifically allocated tribal lands. This allows historically marginalizing policies of land allocation by the United States government to continue to determine harmful land use practices in Native American communities. For example, the Greater Chaco Canyon region, which spans across Arizona, Colorado, New Mexico, and Utah, is home to ancient Puebloan architecture, extremely significant grounds to descendant indigenous groups. Most of these lands, however, are controlled by the United States Forest Service (USFS) and the Bureau of Land Management (BLM), leaving them vulnerable to development from the oil sector. These organizations, particularly the BLM, have a recent history of allowing oil companies to exploit the resources beneath federal lands.

One significant roadblock to meaningful fracking legislation lies in the industry being relegated as a state-level decision. Without federal oversight, the Safe Drinking Water Act (SDWA), the Resource Conservation and Recovery Act (RCRA), the Clean Water Act (CWA), and the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) omit fracking activity from their respective languages.

There are numerous scientific limitations to the study of the environmental impact of hydraulic fracturing. The main limitation is the difficulty in developing effective monitoring procedures and protocols, for which there are several main reasons:

• Variability among fracturing sites in terms of ecosystems, operation sizes, pad densities, and quality-control measures makes it difficult to develop a standard protocol for monitoring.
• As more fracturing sites develop, the chance for interaction between sites increases, greatly compounding the effects and making monitoring of one site difficult to control. These cumulative effects can be difficult to measure, as many of the impacts develop very slowly.
• Due to the vast number of chemicals involved in hydraulic fracturing, developing baseline data is challenging. In addition, there is a lack of research on the interaction of the chemicals used in hydraulic fracturing fluid and the fate of the individual components.