Salty bromide concentrations in the Monongahela River, which had risen in 2009 and 2010 due, at least in part, to discharges of Marcellus Shale gas drilling wastewater by sewage treatment plants, returned to normal levels in 2011 and this year, according to a Carnegie Mellon University river monitoring study.
The findings are good news for municipal water suppliers concerned that the higher levels of bromide, a nontoxic salt compound, were reacting with chlorine in the water disinfection process to produce higher than healthy concentrations of a carcinogen, trihalomethane, in the finished water supplied to their customers.
Eleven public water utilities use the Monongahela River to supply water to about 1 million people.
Jeanne VanBriesen, director of the Center for Water Quality in Urban Environmental Systems (Water QUEST) and a professor in the Department of Civil & Environmental Engineering, said the decline in Mon River bromide levels coincided with a request to drilling companies by the state Department of Environmental Protection to stop using the sewage treatment plants, which are not equipped to treat the drilling wastes.
"Bromide concentrations have declined, and there are reduced loads entering the river. We don't know why, but the decline corresponds to the DEP's request that treatment plants stop accepting drilling wastewater," said Ms. VanBriesen, who discussed the study results at the third annual CMU "State of the Monongahela River Research Forum," last week.
The CMU study sampled river water for chloride and bromide, elements that are components of total dissolved solids, or TDS, at eight locations near public drinking water intakes. She said the study found bromide discharges continue to be an issue from coal-fired power plants and mines.
Bromide concentrations remain high near several commercial brine and wastewater treatment plants on the Allegheny River, where the Pittsburgh Water and Sewer Authority draws water for its 400,000 customers. According to the authority's 2011 water quality report, trihalomethane levels were measured at 18 to 106 parts per billion, but the systemwide annual average was 66 parts per billion, below the federally allowed maximum of 80 parts per billion.
The Ohio River Valley Water Sanitation Commission designated bromide as a "compound of concern" for water treatment plants last year.
Other research found that the higher TDS levels may have reduced the number of smaller minnow-sized fish in the river. According to a fish survey by California University of Pennsylvania researchers David Argent and William Kimmel, populations of larger fish in the river have been stable since 2005, but three species of darters -- rainbow darter, channel darter and johnny darter -- have all declined significantly in number.
"The small-bodied benthic fishes have declined markedly," Mr. Argent said. "The reason for the changes is unknown, but during that time there has been elevated total dissolved solids, and that seems to be having some effect."
High TDS levels in the river in 2008, 2009, and 2010 caused concerns from industries that couldn't use the contaminated water in their industrial processes and from water utility customers who complained about bad tasting and smelling water that damaged their automatic dishwashers and left spots on their glassware.