HARRISBURG, Pa. -- Amid criticism from environmentalists and growing concern from scientists, Pennsylvania on Tuesday asked the state's booming natural gas industry to halt disposing of millions of gallons of contaminated drilling wastewater through treatment plants that discharge into rivers and streams.
The plants are ill-equipped to remove pollutants from the wastewater -- which is intensely salty and tainted with chemicals. The state Department of Environmental Protection said recent water tests suggest the discharges could harm drinking water supplies and, eventually, human health.
The DEP set a May 19 deadline for drillers to stop bringing the waste to the treatment plants. It did not say how the wastewater should be disposed of in the future.
The announcement was a major change in the state's regulation of gas drilling that has swept Pennsylvania since 2008, when energy companies began swarming the state for the vast riches of the Marcellus Shale formation, the nation's largest known natural gas reservoir. It came the same day that an industry group, the Marcellus Shale Coalition, said it now believes drilling wastewater is partly at fault for rising levels of bromide being found in Pittsburgh-area rivers.
Drillers free natural gas from the dense shale rock using millions of gallons of chemical-laden water in a process called hydraulic fracturing, or fracking. As the practice as rapidly grown in Pennsylvania, especially in the southwestern corner, the state has scrambled to adapt its regulations.
In other major gas-drilling states, gas drillers inject the wastewater deep underground into disposal wells. But in Pennsylvania, some drilling wastewater is trucked from drilling sites to sewer authorities and industrial treatment plants, mainly in western Pennsylvania, and discharged into rivers that provide drinking water for hundreds of thousands of people.
Pennsylvania has allowed hundreds of millions of gallons of the partially treated wastewater, largely through at least 15 plants, to be discharged into rivers from which communities draw drinking water. New tests show elevated levels of bromide in western Pennsylvania rivers, the agency said.
"Now is the time to take action to end this practice," acting Department of Environmental Protection Secretary Michael Krancer said in a statement Tuesday.
Bromide is a salt that reacts with the chlorine disinfectants used by drinking water systems and creates trihalomethanes, which have been linked to cancer when given in high doses to laboratory animals.
There is scientific uncertainty as to whether the low levels of trihalomethanes sometimes found in chlorinated drinking water have any potential to cause cancer, liver or central nervous system damage in humans. But the U.S. Environmental Protection Agency has decided that there is enough concern to label the contaminants a potential hazard, and limit the amount of the substance allowed in drinking water.