Buried in Duke Energy’s $102 million settlement of federal charges linked to coal ash this month is an unrelated provision that might cost Duke even more money.
Duke agreed to a claims process for municipal water systems affected by power-plant scrubbers that make air emissions cleaner.
The massive scrubbers also capture chemical compounds called bromides. Bromides, which are in the coal the power plants burn, come out of the scrubbers in wastewater that drains to rivers or lakes.
That’s where problems can start. Bromides aren’t toxic, or regulated, but can react with chlorine used to disinfect drinking water.
The reaction forms compounds called trihalomethanes. THMs can cause liver, kidney or central nervous system problems and increased cancer risks.
Other naturally-occurring materials in water, such as tree leaves, can also form THMs. But scrubbers appear to be to blame for problems in at least two North Carolina towns.
When Duke installed scrubbers at its Belews Creek power plant in Stokes County in 2008, court filings say, the Dan River town of Eden soon saw a leap in THMs.
Duke later agreed to pay Eden $2.3 million and Madison, which also draws water from the Dan, $770,000 to modify their treatment systems.
Those cases are part of an emerging bromide issue for the nation’s utilities as the Environmental Protection Agency probes the sources of THMs.
Duke says no technology exists to capture bromides from scrubbers, but the company is working on a solution with UNC Charlotte researchers.
Duke has identified its Cliffside power plant, on the Broad River west of Charlotte, as another potential problem. Like Belews Creek, Cliffside is a large plant on a shallow river that can’t readily dilute bromides.
Duke installed scrubber equipment to reduce the plant’s bromide discharge. Tests of the Broad in 2013 found no significant levels, spokeswoman Erin Culbert said.
Duke officials don’t know of any water systems downstream of Cliffside with high THMs “but acknowledge the possibility that one or more communities may have been affected,” court papers say.
Gaffney, S.C., is downstream but uses the Broad as a backup water source, mostly in summer. “We haven’t had any problems with it,” said Donnie Hardin, general manager of the city’s public works board.
Bromides in saltwater can also cause problems in coastal areas, but a North Carolina water-supply official said few water systems have reported major problems with them.
The Duke claims process puts the burden on local governments to prove that the company’s bromides “substantially contributed” to a THM spike. A court-appointed monitor will decide whether to award restitution, and either side can appeal to federal court.
Two Duke power plants close to Charlotte – Marshall on Lake Norman and Allen on Lake Wylie – also have scrubbers.
The state Public Water Supply Section recommended that discharge permits now under review require Duke to regularly test wastewater for bromides at both power plants.
“I would probably say that anybody downstream of a scrubber where there is a bromide discharge probably has an interest,” said section chief Jessica Godreau.
Culbert said Norman and Wylie “are such large reservoirs that it would be very surprising if we had an impact even to the level (water systems) would notice.”
Duke also expects little downstream impact from its other scrubber-equipped power plants: Asheville, where the coal-fired units will be retired by 2020, and the Roxboro and Mayo plants in north-central North Carolina.