Special issue: Understanding the risks of unconventional shale gas development.

Development A in methods for hydraulic fracturing, horizontal drilling, and related technologies that enable the recovery of natural gas and oil from deep shale formations have been ongoing for decades. However, it is primarily in the past few years that the evolution of this technology and its more widespread deployment in areas unaccustomed to recent oil and gas activity, such as in the eastern United States, has led to concern and controversy. Proponents argue that the shale gas revolution has enabled a new era of clean domestic energy, bringing significant economic benefits and jobs to those who need them and reducing U.S. greenhouse gas (GHG) emissions, while posing modest environmental risks similar to those of other natural gas and energy development technologies. Furthermore, they believe these risks to be well-managed by the current mix of drillers and operators utilizing ongoing improvements in technology and industry standards for best practice, together with the current set of governmental regulations. In contrast, opponents of “fracking” argue that it poses significant upstream, operational and downstream risks, and is currently implemented with inadequate safeguards and monitoring to protect against multiple environmental, human health, and socioeconomic impacts. Theymaintain that GHG emissions may increase in the long term due to shale gas, and that the emerging system of non-Federal (state-based) regulation in the U.S. exhibits high variability and inconsistency across states, with inadequate capacity for effective tracking, coordination and oversight of risks. Is there sufficient experience and scientific evidence to support or refute these opposing claims and narratives? Where is additional research most needed to provide the critical knowledge for improved understanding and management of shale gas technology, its risks, and its governance? Given the rapidly evolving technology and deployment of unconventional shale gas drilling, an assessment of the current state of knowledge of its risks and governance elements−and how they interact over different spatial, temporal, and organizational scales−is critically needed. The objective of this special issue is to begin to provide such an assessment. The papers in this issue were derived from two workshops organized in 2013 at the U.S. National Research Council (NRC), the first on risks and the second on risk governance. With support from the National Science Foundation, the Park Foundation, and Shell Upstream America, the NRC assembled a committee to plan the workshops and invited scholars and practitioners from academia, oil and gas companies, and state, federal and local agencies. The presentations at the workshops and the resulting collection of papers in this special issue review and assess the depth and breadth of science behind risk and risk governance approaches that academics, industry professionals and governmental regulators are beginning to bring to bear on this technology, which extends well beyond the confines of any single field of environmental science. The insights presented here include those of leading water, air and ecosystem scientists, geologists, engineers, health scientists, economists, social scientists, and experts in law and political science. ES&T provides an especially appropriate venue for such a special issue, given its broad and leading coverage of environmental science, engineering, and policy. The first feature article in this special issue, by Small et al., summarizes key elements of the technical-social system of shale gas development, its risks, and their governance. For each principal domain of risk, the authors identify known or potential hazards and promisingmitigation options. A first attempt is made to characterize the current state of knowledge about the risk and risk governance issues, including critical research needs. Risk domains considered include operational risks (accidents, leakage, and induced seismicity); impacts on water supply and water quality; local, regional, and global air pollution impacts; effects on global climate change; ecological effects associated with habitat disruption and toxicity; human health effects; and socioeconomic impacts on affected communities. Following this lead-off paper are papers that provide in-depth reviews of water resource impacts; air quality effects; effects on global climate change; potential human health implications; and socioeconomic risks to communities. In their review of water-related risks, Vengosh et al. identify potential impacts from (a) contamination of shallow aquifers by “stray gases,” which can evolve into salinization of shallow groundwater through leaking natural gas wells; (b) contamination of surface water and shallow groundwater from spills, leaks, and disposal of inadequately treated wastewater or hydraulic fracturing fluids; (c) accumulation of toxic and radioactive elements in soil or stream sediments; and (d) overextraction of water resources that could induce water shortages or conflicts with other water users. In the domain of air quality impacts, Moore et al. find that new research is needed to estimate emissions of air pollutants from shale gas production, including measurements before and during production, processing, transmission, storage, and distribution, as well as rarely quantified emissions from retired and abandoned wells. Newell and Raimi offer one of the first comprehensive analyses of the effects of both methane leakage and the economic forces affecting shale-gas related greenhouse gas emissions, including a likely increase in overall energy use due to lower prices, a shortterm decrease in GHG emissions due to displacement of coal by natural gas (already apparent in the U.S.), and projected longerterm effects due to displacement or delay of coal and oil, but also zero-carbon sources such as nuclear and renewables. While abundant natural gas does not drive economy-wide emissions to zero, having a low-cost alternative to more carbon-intensive fuels such as coal and oil can make it cheaper for society to achieve broad climate policies. Additional comprehensive analyses of the effects of shale gas development on global demand for fossil fuels and fuel switching are thus clearly needed.