Rarely does a new form of energy — shale gas — have such a dizzying range of potential impacts, good and bad. It could significantly increase America’s level of energy independence and help transition us to a lower-carbon future, but one of its major components, methane, is a highly potent greenhouse gas.
As the journal Nature has reported, research teams continue to find that methane leaks resulting from the natural gas extraction process pose significant environmental problems. That the United States has large deposits of shale gas is a blessing for consumers, but exploiting them could have significant environmental and health impacts, including air and water pollution as well as long-term risks such as cancer and respiratory illnesses. Even earthquakes have been reported.
Part of the risk from shale gas comes from how it’s extracted: Hydraulic fracturing — better known as fracking — involves drilling down vertically through hundreds of feet of rock and then horizontally through the shale bed. Millions of gallons of rock, sand and chemicals are then pumped down under high pressure to “frack” the shale bed, releasing the natural gas trapped within it. But in drilling down to the deposits, wells often pass through aquifers that provide water to communities, plants and wildlife on the surface. Leakage of shale gas into water supplies isn’t supposed to happen, but reports may indicate otherwise.
And while the surface impacts of natural-gas extraction are nothing compared to, say, mountaintop removal coal mining, they can be considerable, and deposits’ location frequently magnifies the problem — for example, the Barnet Shale, one of the richest in the U.S., underlies the entire Dallas-Fort Worth metropolitan area. Residents often have little say over how gas wells are run, even those on their own property, and truck traffic can be considerable as water is trucked in and waste trucked out. And as droughts intensify, concerns rise over the massive quantities of water required to extract for hydraulic fracturing.
In February 2013, the EPA reported that petroleum and natural gas systems, including fracking, constituted the second largest sector in terms of greenhouse gas emissions. (See EPA’s interactive map to locate these facilities.)
Journalists and researchers have dug deep into the issue. To name just a few: Andrew Revkin, author of the New York Times‘ “Dot Earth” blog, has had much to say about the potential health impacts of shale gas; Tom Wilber, author of Under the Surface, has been tracking the issue; at ProPublica, Abrahm Lustgarten and others have published many investigative pieces on fracking and curated a collection of other journalistic work; Bryan Walsh of Time has covered the issue closely.
Nature magazine has also produced a helpful point-counterpoint to illustrate the legitimate concerns of those on both sides of the issue. Meanwhile, the EPA continues to study the impacts on drinking water resources.
Below is a selection of studies that provide insight into the potential health impacts of shale gas extraction and fracking:
“Impact of Shale Gas Development on Regional Water Quality”
Vidic, R.D.; Brantley, S.L.; Vandenbossche, J.M.; Yoxtheimer, D.; Abad, J.D. Science, May 2013, Vol. 340, No. 6134. doi: 10.1126/science.1235009.
Abstract: “Unconventional natural gas resources offer an opportunity to access a relatively clean fossil fuel that could potentially lead to energy independence for some countries. Horizontal drilling and hydraulic fracturing make the extraction of tightly bound natural gas from shale formations economically feasible. These technologies are not free from environmental risks, however, especially those related to regional water quality, such as gas migration, contaminant transport through induced and natural fractures, wastewater discharge, and accidental spills. We review the current understanding of environmental issues associated with unconventional gas extraction. Improved understanding of the fate and transport of contaminants of concern and increased long-term monitoring and data dissemination will help manage these water-quality risks today and in the future.”
“Methane Contamination of Drinking Water Accompanying Gas-Well Drilling and Hydraulic Fracturing” Osborn, Stephen G.; Vengosh, Avner; Warner, Nathaniel R.; Jackson, Robert B. Proceedings of the National Academy of Sciences, May 2011. doi: 10.1073/pnas.1100682108.
Findings: “Directional drilling and hydraulic-fracturing technologies are dramatically increasing natural-gas extraction. In aquifers overlying the Marcellus and Utica shale formations of northeastern Pennsylvania and upstate New York, we document systematic evidence for methane contamination of drinking water associated with shalegas extraction. In active gas-extraction areas (one or more gas wells within 1 km), average and maximum methane concentrations in drinking-water wells increased with proximity to the nearest gas well and were 19.2 and 64 mg CH4 L-1 (n = 26), a potential explosion hazard; in contrast, dissolved methane samples in neighboring nonextraction sites (no gas wells within 1 km) within similar geologic formations and hydrogeologic regimes averaged only 1.1 mgL-1 (P < 0.05; n = 34).”
“Blind Rush? Shale Gas Boom Proceeds Amid Human Health Questions” Schmidt, Charles W. Environmental Health Perspectives, August 2011; 119(8): a348-a353. doi: 10.1289/ehp.119-a348.
Excerpt: “Is the country ready for full-tilt fracking? That’s debatable. Shale gas clearly has its benefits: it’s domestically produced, it generates jobs and billions of dollars in revenue, and it could arguably lower the country’s greenhouse gas emissions. Natural gas emits less carbon dioxide per unit burned than coal and gasoline, but in its unburned state, it is itself a more potent greenhouse gas than carbon dioxide. Because of that, experts debate its climate benefits. Some states, among them Texas and Pennsylvania, have embraced shale gas as a revenue source that might boost sagging economies. Other states are taking a more cautious approach. For instance, Maryland tried to impose a two-year moratorium on fracking that failed in the state’s Senate.”
“Human Health Risk Assessment of Air Emissions from Development of Unconventional Natural Gas Resources” McKenzie, Lisa M.; Witter, Roxana Z.; Newman, Lee S.; Adgate, John L. Science of the Total Environment, May 2012, Vol. 424, 79-87.
Findings: “Residents living ≤ 1/2 mile from wells are at greater risk for health effects from [natural gas development] than are residents living >1/2 mile from wells. Subchronic exposures to air pollutants during well completion activities present the greatest potential for health effects. The subchronic non-cancer hazard index (HI) of 5 for residents ≤ 1/2 mile from wells was driven primarily by exposure to trimethylbenzenes, xylenes, and aliphatic hydrocarbons. Chronic HIs were 1 and 0.4. for residents ≤ 1/2 mile from wells and > 1/2 mile from wells, respectively. Cumulative cancer risks were 10 in a million and 6 in a million for residents living ≤ 1/2 mile and > 1/2 mile from wells, respectively, with benzene as the major contributor to the risk.”
“Research and Policy Recommendations for Hydraulic Fracturing and Shale-Gas Extraction” Jackson, Robert B.; Pearson, Brooks Rainey; Osborn, Stephen G.; Warner, Nathaniel R.; Vengosh, Avner. Center on Global Change, Duke University, May 2011.
Findings: “The potential for [aquifer] contamination from wastewaters associated with hydraulic fracturing depends on many factors, including the toxicity of the fracturing fluid and the produced waters, how close the gas well and fractured zone are to shallow ground water, and the transport and disposal of wastewaters. Despite precautions by industry, contamination may sometimes occur through corroded well casings, spilled fracturing fluid at a drilling site, leaked wastewater, or, more controversially, the direct movement of methane or water upwards from deep underground…. During the first month of drilling and production alone, a single well can produce a million or more gallons of waste water that can contain pollutants in concentrations far exceeding those considered safe for drinking water and for release into the environment. These pollutants sometimes include formaldehyde, boric acid, methanol, hydrochloric acid, and isopropanol, which can damage the brain, eyes, skin, and nervous system on direct contact. Another potential type of contamination comes from naturally occurring salts, metals, and radioactive chemicals found deep underground.”
“Natural Gas Operations from a Public Health Perspective” Colborn, Theo; Kwiatkowski, Carol; Schultz, Kim; Bachran, Mary. Human and Ecological Risk Assessment, September 2011, 1039-1056. doi: 10.1080/10807039.2011.605662.
Abstract: “The technology to recover natural gas depends on undisclosed types and amounts of toxic chemicals. A list of 944 products containing 632 chemicals used during natural gas operations was compiled. Literature searches were conducted to determine potential health effects of the 353 chemicals identified by Chemical Abstract Service (CAS) numbers. More than 75% of the chemicals could affect the skin, eyes, and other sensory organs, and the respiratory and gastrointestinal systems. Approximately 40% to 50% could affect the brain/nervous system, immune and cardiovascular systems, and the kidneys; 37% could affect the endocrine system; and 25% could cause cancer and mutations. These results indicate that many chemicals used during the fracturing and drilling stages of gas operations may have long-term health effects that are not immediately expressed. In addition, an example was provided of waste evaporation pit residuals that contained numerous chemicals on the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and Emergency Planning and Community Right-to-Know Act (EPCRA) lists of hazardous substances.”
“Geochemical Evidence for Possible Natural Migration of Marcellus Formation Brine to Shallow Aquifers In Pennsylvania” Warner, Nathaniel R.; et al. Proceedings of the National Academy of Sciences, May 2012. doi: 10.1073/pnas.1121181109.
Abstract: “We present geochemical evidence from northeastern Pennsylvania showing that pathways, unrelated to recent drilling activities, exist in some locations between deep underlying formations and shallow drinking water aquifers…. The occurrences of saline water do not correlate with the location of shale-gas wells and are consistent with reported data before rapid shale-gas development in the region; however, the presence of these fluids suggests conductive pathways and specific geostructural and/or hydrodynamic regimes in northeastern Pennsylvania that are at increased risk for contamination of shallow drinking water resources, particularly by fugitive gases, because of natural hydraulic connections to deeper formations.”
“Potential Contaminant Pathways from Hydraulically Fractured Shale to Aquifers” Myers, T. Ground Water, 2012. doi: 10.1111/j.1745-6584.2012.00933.x.
Abstract: “Hydraulic fracturing of deep shale beds to develop natural gas has caused concern regarding the potential for various forms of water pollution. Two potential pathways — advective transport through bulk media and preferential flow through fractures — could allow the transport of contaminants from the fractured shale to aquifers. There is substantial geologic evidence that natural vertical flow drives contaminants, mostly brine, to near the surface from deep evaporite sources. Interpretative modeling shows that advective transport could require up to tens of thousands of years to move contaminants to the surface, but also that fracking the shale could reduce that transport time to tens or hundreds of years. Conductive faults or fracture zones, as found throughout the Marcellus shale region, could reduce the travel time further. Injection of up to 15,000,000 [liters] of fluid into the shale generates high pressure at the well, which decreases with distance from the well and with time after injection as the fluid advects through the shale. The advection displaces native fluids, mostly brine, and fractures the bulk media widening existing fractures. Simulated pressure returns to pre-injection levels in about 300 [days]. The overall system requires from 3 to 6 years to reach a new equilibrium reflecting the significant changes caused by fracking the shale, which could allow advective transport to aquifers in less than 10 years. The rapid expansion of hydraulic fracturing requires that monitoring systems be employed to track the movement of contaminants and that gas wells have a reasonable offset from faults.”
“Carbon and Hydrogen Isotopic Evidence for the Origin of Combustible Gases in Water-supply Wells in North-central Pennsylvania” Révész, Kinga M.; Breen, Kevin J.; Baldassare, Alfred J.; Burruss, Robert C. Applied Geochemistry, December 2010, Vol. 25, Issue 12. doi: 10.1016/j.apgeochem.2010.09.011.
Abstract: “The origin of the combustible gases in groundwater from glacial-outwash and fractured-bedrock aquifers was investigated in northern Tioga County, Pennsylvania. Thermogenic methane (CH4) and ethane (C2H6) and microbial CH4 were found. Microbial CH4 is from natural in situ processes in the shale bedrock and occurs chiefly in the bedrock aquifer. The δ13C values of CH4 and C2H6 for the majority of thermogenic gases from water wells either matched or were between values for the samples of non-native storage-field gas from injection wells and the samples of gas from storage-field observation wells. Traces of C2H6 with microbial CH4 and a range of C and H isotopic compositions of CH4 indicate gases of different origins are mixing in sub-surface pathways; gas mixtures are present in groundwater. Pathways for gas migration and a specific source of the gases were not identified. Processes responsible for the presence of microbial gases in groundwater could be elucidated with further geochemical study.”
“Annual Energy Outlook 2012″ U.S. Energy Information Administration, Office of Integrated and International Energy Analysis, U.S. Department of Energy, Washington, D.C.
Summary: “Much of the growth in natural gas production in the AEO2012 Reference case results from the application of recent technological advances and continued drilling in shale plays with high concentrations of natural gas liquids and crude oil, which have a higher value than dry natural gas in energy equivalent terms. Shale gas production increases in the Reference case from 5.0 trillion cubic feet per year in 2010 (23% of total U.S. dry gas production) to 13.6 trillion cubic feet per year in 2035 (49% of total U.S. dry gas production). As with tight oil, when looking forward to 2035, there are unresolved uncertainties surrounding the technological advances that have made shale gas production a reality. The potential impact of those uncertainties results in a range of outcomes for U.S. shale gas production from 9.7 to 20.5 trillion cubic feet per year when looking forward to 2035. As a result of the projected growth in production, U.S. natural gas production exceeds consumption early in the next decade in the Reference case. The outlook reflects increased use of liquefied natural gas in markets outside North America, strong growth in domestic natural gas production, reduced pipeline imports and increased pipeline exports, and relatively low natural gas prices in the United States.”
Tags: pollution, greenhouse gases, fossil fuels, coal, research roundup