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.^[1] Research has determined that fracking negatively affects human health and drives climate change.^[2][3][4]

Fracking fluids include proppants and other substances, which include chemicals known to be toxic, as well as unknown chemicals that may be toxic.^[5] 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.^[6][7] In other jurisdictions, such as the United Kingdom, these chemicals must be made public and their applications are required to be nonhazardous.^[8]

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.^[9] 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.^[10][11] 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.^[12] 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.^[13]

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.^[14]

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.^{[15][16]: 3–7} In some countries like France a precautionary approach has been favored and fracking has been banned.^[17][18] 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.^[15] 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.^[19][20][21]

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.^[13] 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.^[22]

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.^[23]

"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."^[24]

Also transportation of necessary water volume for hydraulic fracturing, if done by trucks, can cause emissions.^[25] Piped water supplies can reduce the number of truck movements necessary.^[26]

A report from the Pennsylvania Department of Environmental Protection indicated that there is little potential for radiation exposure from oil and gas operations.^[27]

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.^[23] Thirty seven percent of the chemicals used in hydraulic fracturing operations are volatile and can become airborne.^[23]

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.^[28] 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.^[28]

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.^[40][41] An average well requires 3 to 8 million US gallons (11,000 to 30,000 m³) of water over its lifetime.^{[41][42][43][44]} 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.^[45] 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."^[46]

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.^[15] A 2011 report from the Tyndall Centre estimates that to support a 9 billion cubic metres per annum (320×10^⁹ cu ft/a) gas production industry, between 1.25 to 1.65 million cubic metres (44×10^⁶ to 58×10^⁶ cu ft) would be needed annually,^[47] 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,^[49] and in drought-prone Texas, in North America.^[50] It may also require water overland piping from distant sources.^[43]

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.^[51]

Some producers have developed hydraulic fracturing techniques that could reduce the need for water.^[52] Using carbon dioxide, liquid propane or other gases instead of water have been proposed to reduce water consumption.^[53] 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.^[52] Recycled flowback water can be reused in hydraulic fracturing.^[30] 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.^[54]

There are naturally occurring radioactive materials (NORM), for example radium, radon,^[85] uranium, and thorium,^[60][86][87] in shale deposits.^[66] 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.^[66][88][89] 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.^[90][91] A report from the Pennsylvania Department of Environmental Protection indicated that there is little potential for radiation exposure from oil and gas operations.^[27]

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.^[92] 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) ^[93] 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.^[94] 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.^[95]

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.^[96] 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).^[97]

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.^[13] 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.^[111] For example, the low-frequency noise that comes from well pumps contributes to irritation, unease, and fatigue.^[112]

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.^[113]

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.^[114]

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.^[115] 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.^[116] 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.^[117]

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.^[118] 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.^[119] 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.^[120]

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.^[121] 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.^[121]

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.^{[16]: 3–7}

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.^[122] 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.^[123]

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.^[17][18] 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.^[15][124] 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.^[84]

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.^[125] 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.^[125]

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.^[126]

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.^[127]
• 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.^[128]
• 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.^[129]