The extraction and use of shale gas can affect the environment through the leaking of extraction chemicals and waste into water supplies, the leaking of
greenhouse gases during extraction, and the pollution caused by the improper processing of natural gas . A challenge to preventing pollution is that shale gas extractions varies widely in this regard, even between different wells in the same project; the processes that reduce pollution sufficiently in one extraction may not be enough in another.
Climate Barack Obama's administration had sometimes promoted shale gas, in part because of its belief that it releases fewer
greenhouse gas (GHG) emissions than other fossil fuels. In a 2010 letter to President Obama,
Martin Apple of the
Council of Scientific Society Presidents cautioned against a national policy of developing shale gas without a more certain scientific basis for the policy. This umbrella organization that represents 1.4 million scientists noted that shale gas development "may have greater GHG emissions and environmental costs than previously appreciated." In late 2010, the U.S. Environmental Protection Agency issued a report which concluded that shale gas emits larger amounts of
methane, a potent
greenhouse gas, than does conventional gas, but still far less than coal. Methane is a powerful greenhouse gas, although it stays in the atmosphere for only one tenth as long a period as carbon dioxide. Recent evidence suggests that methane has a
global warming potential (GWP) that is 105-fold greater than carbon dioxide when viewed over a 20-year period and 33-fold greater when viewed over a 100-year period, compared mass-to-mass. Several studies which have estimated lifecycle methane leakage from shale gas development and production have found a wide range of leakage rates, from less than 1% of total production to nearly 8%. A 2011 study published in
Climatic Change Letters claimed that the production of electricity using shale gas may lead to as much or more
life-cycle GWP than electricity generated with oil or coal. In the peer-reviewed paper,
Cornell University professor
Robert W. Howarth, a marine ecologist, and colleagues claimed that once
methane leak and venting impacts are included, the life-cycle greenhouse gas footprint of shale gas is far worse than those of coal and fuel oil when viewed for the integrated 20-year period after emission. On the 100-year integrated time frame, this analysis claims shale gas is comparable to coal and worse than fuel oil. However, other studies have pointed out flaws with the paper and come to different conclusions. Among those are assessments by experts at the U.S. Department of Energy, peer-reviewed studies by Carnegie Mellon University and the University of Maryland, and the
Natural Resources Defense Council, which claimed that the Howarth et al. paper's use of a 20-year time horizon for global warming potential of methane is "too short a period to be appropriate for policy analysis." In January 2012, Howarth's colleagues at Cornell University, Lawrence Cathles et al., responded with their own peer-reviewed assessment, noting that the Howarth paper was "seriously flawed" because it "significantly overestimate[s] the fugitive emissions associated with unconventional gas extraction, undervalue[s] the contribution of 'green technologies' to reducing those emissions to a level approaching that of conventional gas, base[s] their comparison between gas and coal on heat rather than electricity generation (almost the sole use of coal), and assume[s] a time interval over which to compute the relative climate impact of gas compared to coal that does not capture the contrast between the long residence time of CO2 and the short residence time of methane in the atmosphere." The author of that response, Lawrence Cathles, wrote that "shale gas has a GHG footprint that is half and perhaps a third that of coal," based upon "more reasonable leakage rates and bases of comparison." In April 2013 the U.S. Environmental Protection Agency lowered its estimate of how much methane leaks from wells, pipelines and other facilities during production and delivery of natural gas by 20 percent. The EPA report on greenhouse emissions credited tighter pollution controls instituted by the industry for cutting an average of 41.6 million metric tons of
methane emissions annually from 1990 through 2010, a reduction of more than 850 million metric tons overall. The Associated Press noted that "The EPA revisions came even though natural gas production has grown by nearly 40 percent since 1990." Using data from the Environmental Protection Agency's 2013 Greenhouse Gas Inventory yields a methane leakage rate of about 1.4%, down from 2.3% from the EPA's previous Inventory.
Life cycle comparison for more than global warming potential A 2014 study from Manchester University presented the "First full life cycle assessment of shale gas used for electricity generation." By full life cycle assessment, the authors explained that they mean the evaluation of nine environmental factors beyond the commonly performed evaluation of global warming potential. The authors concluded that, in line with most of the published studies for other regions, that shale gas in the United Kingdom would have a global warming potential "broadly similar" to that of conventional North Sea gas, although shale gas has the potential to be higher if fugitive methane emissions are not controlled, or if per-well ultimate recoveries in the UK are small. For the other parameters, the highlighted conclusions were that, for shale gas in the United Kingdom in comparison with coal, conventional and liquefied gas, nuclear, wind and solar (PV). • Shale gas worse than coal for three impacts and better than renewables for four. • It has higher photochemical smog and terrestrial toxicity than the other options. • Shale gas a sound environmental option only if accompanied by stringent regulation. Dr James Verdon has published a critique of the data produced, and the variables that may affect the results.
Water and air quality Chemicals are added to the water to facilitate the underground fracturing process that releases natural gas. Fracturing fluid is primarily water and approximately 0.5% chemical additives (friction reducer, agents countering
rust, agents killing microorganism). Since (depending on the size of the area) millions of liters of water are used, this means that hundreds of thousands of liters of chemicals are often injected into the subsurface. About 50% to 70% of the injected volume of contaminated water is recovered and stored in above-ground ponds to await removal by tanker. The remaining volume remains in the subsurface. Hydraulic fracturing opponents fear that it can lead to contamination of
groundwater aquifers, though the industry deems this "highly unlikely". However, foul-smelling odors and
heavy metals contaminating the local water supply above-ground have been reported. Besides using water and industrial chemicals, it is also possible to frack shale gas with only liquified
propane gas. This reduces the
environmental degradation considerably. The method was invented by GasFrac, of Alberta, Canada. Hydraulic fracturing was exempted from the Safe Drinking Water Act in the
Energy Policy Act of 2005. A study published in May 2011 concluded that shale gas wells have seriously contaminated shallow groundwater supplies in
northeastern Pennsylvania with flammable
methane. However, the study does not discuss how pervasive such contamination might be in other areas drilled for shale gas. The
United States Environmental Protection Agency (EPA) announced 23 June 2011 that it will examine claims of water pollution related to hydraulic fracturing in Texas, North Dakota, Pennsylvania, Colorado and Louisiana. On 8 December 2011, the EPA issued a draft finding which stated that groundwater contamination in
Pavillion, Wyoming may be the result of fracking in the area. The EPA stated that the finding was specific to the area, where the fracking techniques differ from those used in other parts of the U.S. Doug Hock, a spokesman for the company which owns the gas field, said that it is unclear whether the contamination came from the fracking process. Wyoming's Governor
Matt Mead called the EPA draft report "scientifically questionable" and stressed the need for additional testing. The Casper Star-Tribune also reported on 27 December 2011, that the EPA's sampling and testing procedures "didn't follow their own protocol" according to Mike Purcell, the director of the Wyoming Water Development Commission. A 2011 study by the
Massachusetts Institute of Technology concluded that "The environmental impacts of shale development are challenging but manageable." The study addressed groundwater contamination, noting "There has been concern that these fractures can also penetrate shallow freshwater zones and contaminate them with fracturing fluid, but there is no evidence that this is occurring". This study blames known instances of methane contamination on a small number of sub-standard operations, and encourages the use of industry best practices to prevent such events from recurring. In a report dated 25 July 2012, the U.S. Environmental Protection Agency announced that it had completed its testing of private drinking water wells in Dimock, Pennsylvania. Data previously supplied to the agency by residents, the Pennsylvania Department of Environmental Protection, and Cabot Oil and Gas Exploration had indicated levels of arsenic, barium or manganese in well water at five homes at levels that could present a health concern. In response, water treatment systems that can reduce concentrations of those hazardous substances to acceptable levels at the tap were installed at affected homes. Based on the outcome of sampling after the treatment systems were installed, the EPA concluded that additional action by the Agency was not required. A
Duke University study of
Blacklick Creek (Pennsylvania), carried out over two years, took samples from the creek upstream and down stream of the discharge point of Josephine Brine Treatment Facility.
Radium levels in the sediment at the discharge point are around 200 times the amount upstream of the facility. The radium levels are "above regulated levels" and present the "danger of slow bio-accumulation" eventually in fish. The Duke study "is the first to use isotope hydrology to connect the dots between shale gas waste, treatment sites and discharge into drinking water supplies." The study recommended "independent monitoring and regulation" in the United States due to perceived deficiencies in self-regulation. According to the US Environmental Protection Agency, the Clean Water Act applies to surface stream discharges from shale gas wells: :"6) Does the Clean Water Act apply to discharges from Marcellus Shale Drilling operations? :Yes. Natural gas drilling can result in discharges to surface waters. The discharge of this water is subject to requirements under the Clean Water Act (CWA)."
Earthquakes Hydraulic fracturing routinely produces
microseismic events much too small to be detected except by sensitive instruments. These microseismic events are often used to map the horizontal and vertical extent of the fracturing. However, as of late 2012, there have been three known instances worldwide of hydraulic fracturing, through
induced seismicity, triggering quakes large enough to be felt by people. On 26 April 2012, the
Asahi Shimbun reported that
United States Geological Survey scientists have been investigating the recent increase in the number of
magnitude 3 and greater
earthquake in the midcontinent of the
United States. Beginning in 2001, the average number of earthquakes occurring per year of magnitude 3 or greater increased significantly, culminating in a six-fold increase in 2011 over 20th century levels. A researcher in Center for Earthquake Research and Information of
University of Memphis assumes water pushed back into the
fault tends to cause earthquake by slippage of fault. Over 109 small earthquakes (
Mw 0.4–3.9) were detected during January 2011 to February 2012 in the Youngstown, Ohio area, where there were no known earthquakes in the past. These shocks were close to a deep fluid injection well. The 14 month seismicity included six felt earthquakes and culminated with a 3.9 shock on 31 December 2011. Among the 109 shocks, 12 events greater than
Mw 1.8 were detected by regional network and accurately relocated, whereas 97 small earthquakes (0.4x emissions per MWh than natural gas, and 1–17 times as much NOx per MWh. Lifecycle CO2 emissions from coal plants are 1.8-2.3 times greater (per KWh) than natural gas emissions. The air quality advantages of natural gas over coal have been borne out in Pennsylvania, according to studies by the
RAND Corporation and the
Pennsylvania Department of Environmental Protection. The shale boom in Pennsylvania has led to dramatically lower emissions of sulfur dioxide, fine particulates, and
volatile organic compounds (VOCs).
Landscape impacts Coal mining radically alters whole mountain and forest landscapes. Beyond the coal removed from the earth, large areas of forest are turned inside out and blackened with toxic and radioactive chemicals. There have been reclamation successes, but hundreds of thousands of acres of abandoned surface mines in the United States have not been reclaimed, and reclamation of certain terrain (including steep terrain) is nearly impossible. Where coal exploration requires altering landscapes far beyond the area where the coal is, aboveground natural gas equipment takes up just one percent of the total surface land area from where gas will be extracted. The environmental impact of gas drilling has changed radically in recent years. Vertical wells into conventional formations used to take up one-fifth of the surface area above the resource, a twenty-fold higher impact than current horizontal drilling requires. A six-acre horizontal drill pad can thus extract gas from an underground area 1,000 acres in size. The impact of natural gas on landscapes is even less and shorter in duration than the impact of wind turbines. The footprint of a shale gas derrick (3–5 acres) is only a little larger than the land area necessary for a single wind turbine. But it requires less concrete, stands one-third as tall, and is present for just 30 days instead of 20–30 years. Between 7 and 15 weeks are spent setting up the drill pad and completing the actual hydraulic fracture. At that point, the drill pad is removed, leaving behind a single garage-sized wellhead that remains for the lifetime of the well. 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)
Water With coal mining, waste materials are piled at the surface of the mine, creating aboveground runoff that pollutes and alters the flow of regional streams. As rain percolates through waste piles, soluble components are dissolved in the runoff and cause elevated total dissolved solids (TDS) levels in local water bodies. Acid mine wastewater can drain into groundwater, causing significant contamination. Explosive blasting in a mine can cause groundwater to seep to lower-than-normal depths or connect two aquifers that were previously distinct, exposing both to contamination by mercury, lead, and other toxic heavy metals. Contamination of surface waterways and groundwater with fracking fluids is problematic. Shale gas deposits are generally several thousand feet below ground. There have been instances of methane migration, improper treatment of recovered wastewater, and pollution via reinjection wells. In most cases, the life-cycle water intensity and pollution associated with coal production and combustion far outweigh those related to shale gas production. Coal resource production requires at least twice as much water per million British thermal units compared to shale gas production. And while regions like Pennsylvania have experienced an absolute increase in water demand for energy production thanks to the shale boom, shale wells actually produce less than half the wastewater per unit of energy compared to conventional natural gas. The environmental impact of water consumption at the point of power generation depends on the type of power plant: plants either use evaporative cooling towers to release excess heat or discharge water to nearby rivers. Natural gas combined-cycle power (NGCC), which captures the exhaust heat generated by combusting natural gas to power a steam generator, are considered the most efficient large-scale thermal power plants. One study found that the life-cycle demand for water from coal power in Texas could be more than halved by switching the fleet to NGCC. All told, shale gas development in the United States represents less than half a percent of total domestic freshwater consumption, although this portion can reach as high as 25 percent in particularly arid regions. == Hazards ==