Areas of concern identified by the federal panel included: methane and chemical pollution of groundwater; air pollution; disruption of communities; and cumulative impacts on the environment.
Tensions between the gas industry and local communities have been especially high in Colorado, Texas, and Pennsylvania, where fracking has already been blamed for contaminating drinking water and other groundwater and for polluting the air.
Methane levels were, for instance, found to be 17 times higher in groundwater near areas where shale-gas fracking wells had been drilled in Pennsylvania than in areas where no gas drilling had occurred, according to a peer-reviewed Duke University study of groundwater wells in Pennsylvania and New York earlier this year. Excess methane in water makes the water undrinkable.
Controversy accelerated in recent years when some companies dumped millions of gallons of fracking wastewater into creeks or into municipal sewage systems that were not designed to remove harmful chemicals and other elements.
Into that furor stepped Mr. Obama in May, calling on Energy Secretary Stephen Chu to convene a panel to conduct a 90-day study of the issue as part of the president's “Blueprint for a Secure Energy Future,” an overarching White House plan to curb US oil dependence and shift toward clean energy industries. Shale gas is considered by some to be a “bridge fuel” with about half the carbon dioxide emissions of coal.