In 2011, drillers pumped more than 500 million gallons of toxic fluid into Ohio's injection wells. More than half of the wastewater came from other states.
Research suggests that emissions of methane, a greenhouse gas 20 times more potent than CO2, far exceed current estimates for gas drilling and production.
Watchdog groups have questioned why energy giant TransCanada has been using two different figures for the capacity of its proposed Keystone XL pipeline