MAJOR RISKS FOR WATER CONTAMINATION ASSOCIATED WITH SHALE GAS DEVELOPMENT AND HYDRAULIC FRACTURING

Exploration of unconventional natural gas reservoirs such as low-permeability organic shale formations through horizontal drilling and hydraulic fracturing has changed the energy landscape in the Unites States, providing a vast new energy source. Since the mid-2000s, drilling and production of natural gas has accelerated, also triggering a public debate over the safety and environmental impacts of these operations. Here we highlight two key issues related to water contamination associated with shale gas development. First is stray gas contamination of groundwater; elevated levels of methane with a distinctive isotopic ratio were reported in some shallow drinking water wells and pose a potential flammability or explosion hazard to homes near Marcellus Shale drilling sites in northeastern Pennsylvania. Yet no evidence, so far, has been reported for contamination of dissolved salts in methane-contaminated groundwater. In addition, no evidence for stray gas contamination has reported in shallow groundwater in the Fayetteville Basin in Arkansas. The second major risk is the disposal and/or accidental release (spill) of shale gas wastewater to the environment. Shale gas wastewater is often highly saline and contains high levels of toxic elements including naturally occurring radioactive elements. In spite of treatment, discharge of shale gas wastewater to surface waters in the Appalachian Basin causes direct contamination of the river systems. Disposal of shale gas wastewater can also generate bromide levels above baseline levels in downstream river water. Such bromide levels in surface water can trigger formation of brominated trihalomethanes compounds in downstream drinking waters upon water chlorination. In addition, accumulation of residual contaminants in areas of wastewater disposal, spills, and leaks pose direct health risks. We show that long-term disposal of wastewater originating from shale gas production can cause accumulation of radioactive elements (radium and daughter isotopes) in the river sediments at the disposal sites. Likewise, treatment of shale gas wastewater generates solid waste with potentially high levels of radioactivity. Improper disposal of these solid wastes to unregulated landfills could in some cases contaminate associated water resources.