AN OVERVIEW OF THE RISKS TO WATER RESOURCES FROM HYDRAULIC FRACTURING ­IN THE UNITED SATES

The rise of unconventional shale gas and tight sand oil developments through horizontal drilling and high volume hydraulic fracturing has significantly increased oil and gas exploration in the US and will soon be launched on a global scale. The rapid rate of shale gas and tight oil exploration has triggered an intense public debate regarding the potential environmental and human health effects. Active research by the Duke team in different parts of the USA (Pennsylvania, West Virginia, New York, Arkansas, North Carolina, Texas, Colorado, North Dakota) has identified four potential risks for impacts on water resources: (1) stray gas contamination of shallow aquifers near shale gas sites resulted in elevated methane levels in some drinking water wells located < 1 km from shale gas wells; (2) contamination of surface water and shallow groundwater from accidental spills, leaks, and disposal of inadequately treated oil and gas wastewater resulted in elevated levels of halides, ammonium, barium, radium among other contaminants in downstream waterways, with high potential to trigger the formation of disinfection byproducts in downstream drinking water; (3) accumulation of toxic and radioactive residues in soil and stream sediments near disposal or spill sites; and (4) over-extraction of water resources for drilling and hydraulic fracturing that could induce water shortages and conflicts with other water users, particularly in water-scarce areas like in Texas. While most attention has been made to the risks of anthropogenic chemicals used in hydraulic fracturing, naturally occurring contaminants in formation waters that are extracted with gas and oil such as halides, toxic metals, and radioactive elements pose high risks to the aquatic life and human health in cases where flowback and produced waters from shale gas and tight oil exploration are released to the environment.