Schematic illustration (not to scale) of possible modes of water impacts associated with shale gas development reviewed in the paper: (1) overuse of water that could lead to depletion and water- quality degradation particularly in water-scarce areas; (2) surface water and shallow groundwater contamination from spills and leaks of wastewater storage and open pits near drilling; (3) disposal of inadequately treated wastewater to local streams and accumulation of contaminant residues in disposal sites; (4) leaks of storage ponds that are used for deep-well injection; (5) shallow aquifer contamination by stray gas that originated from the target shale gas formation through leaking well casing. The stray gas contamination can potentially be followed by salt and chemical contamination from hydraulic fracturing fluids and/or formational waters; (6) shallow aquifer contamination by stray gas through leaking of conventional oil and gas wells casing; (7) shallow aquifer contamination by stray gas that originated from intermediate geological formations through annulus leaking of either shale gas or conventional oil and gas wells; (8) shallow aquifer contamination through abandoned oil and gas wells; (9) flow of gas and saline water directly from deep formation waters to shallow aquifers; and (10) shallow aquifer contamination through leaking of injection wells. Credit: ACS, Vengosh et al. Click to enlarge.

Broadly, they found that the published data reveals evidence for stray gas contamination, surface water impacts in areas of intensive shale gas development, and the accumulation of radium isotopes in some disposal and spill sites. However, the direct contamination of shallow groundwater from hydraulic fracturing fluids and deep formation waters by hydraulic fracturing itself remains controversial.

Much of the debate on the possibility of water contamination is related to the availability of baseline water chemistry data in aquifers before shale gas development. Yet full baseline data is often unavailable, given the lack of systematic and component-specific monitoring of private wells and surface water systems across the US. Developing novel geochemical and isotopic tracers that would confirm or refute evidence for contamination can help fill this data gap. The study of water contamination is often based on the characterization of water quality in a regional aquifer and/or surface water away from contamination sites, rather than monitoring water quality changes through time. Retrospective studies of water contamination associated with shale gas development should therefore include a comprehensive investigation of the hydrology, hydrogeology, water chemistry, and isotopic tracers for delineating the sources and mechanisms of water contamination in questioned areas.

Finally, more studies are needed across a broader geographic area, particularly because many shale gas developments occur in areas that have been historically exploited for conventional oil and gas (e.g., PA, WV, CO, TX, and in the future also CA). Most of the scientific publications thus far have addressed water issues in the Appalachian Basin, whereas information for many other basins is limited or not available. Future research should include studies from other basins in order to overcome these gaps and determine the overall risks to water resources from shale-gas development.

Importantly, many of the risks identified in the literature thus far appear possible to mitigate with increased engineering controls during well construction and alternative water-management or water-disposal options to alleviate the impact of shale-gas development on water resources.

—Vengosh et al.

Resources

• Avner Vengosh, Robert B. Jackson, Nathaniel Warner, Thomas H. Darrah, and Andrew Kondash (2014) “A Critical Review of the Risks to Water Resources from Unconventional Shale Gas Development and Hydraulic Fracturing in the United States,” Environmental Science & Technology doi: 10.1021/es405118y