"I think the focus on only shale gas is kind of misleading," Vengosh said, noting that all the wells produce naturally occurring brine water, which can be much saltier than seawater, and also contain heavy metals and natural radiation.
"It's all psychological," Vengosh said of the distinction between shale gas waste and other drilling waste. "That, for me, doesn't make any sense."
The Marcellus Shale lies under parts of Maryland, New York, Ohio, Pennsylvania and West Virginia, and the extraction procedure called hydraulic fracturing, or fracking, has made it possible to tap into deep reserves of oil and gas. The boom in shale gas fracking raised concerns about pollution. Large volumes of water, along with sand and hazardous chemicals, are injected underground to break rock apart and free the oil and gas.
Regulators contend that water and air pollution problems are rare, but environmental groups and some scientists say there hasn't been enough research on these issues. The industry and many federal and state officials say the practice is safe when done properly.
The Water and Sewer Authority report also noted that bromide levels rose in rivers below where some coal-fired power plants discharge wastewater, which can also include bromides.
Dave Mashek, a spokesman for the Pennsylvania Independent Oil and Gas Association, said that state regulators don't set a limit on bromide discharges and that the amount of wastewater that comes from conventional wells is decreasing.
He also noted that the Water and Sewer Authority testing only identified elevated bromide levels in the Allegheny for part of the year, during periods of low river flow.
Kevin Sunday, a spokesman for the Department of Environmental Protection, said many other sources of bromide exist beyond oil and gas wells. He said the volume of wastewater produced by conventional oil and gas wells is substantially lower than what comes from shale gas wells.