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 said it now believes drilling wastewater is partly at fault for rising levels of bromide being found in Pittsburgh-area rivers.
Freeing natural gas from the dense shale rock demands the use of millions of gallons of chemical-laden water in a process called hydraulic fracturing, or fracking. As the practice has rapidly grown in Pennsylvania, especially in the southwestern corner, the state has scrambled to adapt its regulations.
In other major natural gas states, drilling wastewater is injected deep underground into disposal wells. But in Pennsylvania, some drilling wastewater is trucked from well 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. Researchers say that if there is, indeed, an increased cancer risk of drinking water tainted with trihalomethanes, it would come from ingesting consistently high amounts over many years.
Earlier this month, the state expanded the scope of water tests to screen for radioactive pollutants and other contaminants from gas drilling. EPA, which asked for the wider testing, has publicly begun scrutinizing the way Pennsylvania regulates the energy industry's hot pursuit of the Marcellus Shale.
Pennsylvania's former Gov. Tom Ridge, an adviser to the industry group, the Marcellus Shale Coalition, encouraged companies to fall in line, and said that if it's more expensive, then "so be it."
"If it's not mandated, it should be," Ridge told The Associated Press. "I would encourage them to comply as soon as possible, and tomorrow's not a bad time to start."
Paul Hart, the president of Hart Resource Technologies of Creekside, Pa., co-owner of three industrial treatment plants that accept drilling wastewater, said he was surprised by the department's request, and wondered why the agency couldn't give him time to upgrade his plants to address bromides.
"We have already begun to look at treatment methods to reduce bromide levels in our discharges," Hart said. "But it was bit of a surprise because I view it as an overreaction. Even though bromide levels are increasing, they're not at a dangerous level."
His gas drilling clients were just beginning to consider their options, which are likely to be more expensive, he said.
With pressure from state regulators, companies have increasingly sought to reuse drilling water, sometimes using a mobile unit to recycle it at the well site or by trucking it to a facility that treats the water for reuse in drilling. Companies also haul some wastewater to other states, such as Ohio, to inject down disposal wells. Pennsylvania only has a few such disposal wells, and many say the hard Appalachian geology is unlikely to be porous enough to absorb all the wastewater.
A spokesman for one company, Cabot Oil & Gas Corp. of Houston, said it believes it can comply by May 19, while another that has used the treatment plants in the past, Chief Oil & Gas LLC of Dallas, said it already has stopped using them.
Chevron Corp., parent of Pittsburgh-based Atlas Energy Inc., also said it will abide with the DEP's request, and called it "the next logical action for the industry to take."
Officials at Pittsburgh-area drinking water authorities in Beaver Falls and Fredericktown say their facilities have flunked tests for trihalomethanes in the past couple years. Last summer, researchers from Carnegie Mellon University saw a spike in bromides in the Monongahela River, and notified the DEP. The spike in bromides eased, but not down to the level seen previously, said Jeanne M. VanBriesen, who directs Carnegie Mellon's Center for Water Quality in Urban Environmental Systems.
Complicating the matter is that, in addition to gas drilling, Pennsylvania's multitude of coal-fired power plants, abandoned coal mines and other industrial sources are also a major factor in the high salt levels that lead to trihalomethanes in drinking water.
Stanley States, director of water quality and production for the Pittsburgh Water and Sewer Authority, said he began researching the matter last fall after his agency detected higher levels of trihalomethanes in its drinking water. Trihalomethanes, he said, cannot be tasted and do not change the feel of the water.
The authority will keep studying it, but so far, he said, its data indicates that four industrial treatment plants are major contributors to elevated bromide levels in the Allegheny River.
"Those are the chief source," he said. "We haven't seen it from anywhere else."
He suggested that the industrial plants should consider chlorinating their water like the municipal sewage treatment facilities do to kill bacteria and viruses. By doing that, the bromide is forming trihalomethanes at the sewage treatment stage before being released into the river and evaporating there, instead of forming later at the drinking water plant, he said.
Range Resources Corp., the Fort Worth, Texas-based company that is one of the most active in the Marcellus Shale, on Tuesday encouraged drillers to stop taking water to the treatment facilities immediately.
Myron Arnowitt of the environmental advocacy group, Clean Water Action, which had been preparing a lawsuit over the disposal of the wastewater, questioned whether the DEP's action would really stop the practice.
"On the one hand, I think it's good that the DEP is acknowledging that this is a problem," Arnowitt said. "However, if it's as serious a problem as they say it is, it seems they should be ordering the treatment plants to stop accepting the wastewater."
A DEP spokeswoman, Katy Gresh, said the agency hopes to achieve voluntary compliance at the end of 30 days, when it will re-evaluate the matter.
Over the objections of the industry, Pennsylvania imposed tougher wastewater treatment standards for drilling wastewater in August, although it still allowed facilities that had been permitted to accept drilling wastewater before August to continue accepting limited amounts under the same treatment standards. Fifteen of those 27 facilities that were grandfathered under the August rules were still accepting the wastewater, the DEP said.
"While there are several possible sources for bromide other than shale drilling wastewater, we believe that if operators would stop giving wastewater to facilities that continue to accept it under the special provision, bromide concentrations would quickly and significantly decrease," Krancer said in the statement.
Kathryn Klaber, president of the Marcellus Shale Coalition, said Tuesday her organization came to the conclusion that it is partly responsible for higher bromide levels after seeing research from VanBriesen's team and the Pittsburgh Water and Sewer Authority.
Associated Press writer David B. Caruso in New York contributed to this report.