Technology to control air pollution indirectly caused problems for drinking-water plants. But a new legal agreement requires Duke to compensate those who are impacted.
By Gabe Rivin
From 2008 to 2011, the city of Eden had a growing problem with its drinking water.
Some of the city’s distributed water was showing high levels of trihalomethanes, a class of chemicals that are potentially carcinogenic. But staff at the water-treatment plant weren’t sure where the problem was coming from.
So they decided to investigate. After sampling the Dan River, Eden’s source of drinking water, the cause became apparent.
An upstream coal-fired power plant, run by Duke Energy, was releasing bromide into the Dan. Bromide, a byproduct of air pollution-control technology, was then floating downstream, where it was drawn into Eden’s water plant.
Once inside the plant, the bromide mixed with the chemicals in the plant’s disinfection process. This contributed to the formation of trihalomethanes and pushed Eden beyond its legal limits.
Until recently, Duke has been under no obligation to compensate towns and cities for these problems – though Duke has voluntarily compensated Eden and Madison, a nearby town facing similar problems. The Duke money has covered the cost of upgrading water-treatment technology.
But under an agreement finalized in May, Duke has a new legal responsibility. The agreement, part of a plea deal stemming from last February’s coal ash spill, legally requires Duke to pay municipalities whose water has been affected by Duke’s bromide.
Under the plea agreement, Duke must fully repay municipalities that had to spend time to investigate the problem and upgrade their water plants. Duke must also look across the state to find where else this may be an issue.
When chlorine and bromide combine
Trihalomethanes are a byproduct formed when water is disinfected of harmful bacteria and other pathogens.
The U.S. Environmental Protection Agency calls water disinfection “critical” for the public’s health because it kills off microorganisms that can be deadly.
Many municipal plants use chlorine to disinfect water. But chlorine can react with inorganic and organic matter, such as leaves and river grasses, creating trihalomethanes.
But what if the water contains bromide, like the water that Eden was disinfecting? Trihalomethanes can then combine with the ion, forming brominated trihalomethanes.
Health researchers have studied the different classes of trihalomethanes for decades and have found some reasons to be concerned about humans’ exposures to the compounds. A 2009 literature review, for instance, notes that trihalomethane exposure has been associated with an increased risk of bladder cancer. Studies have also associated women’s exposure to trihalomethanes with reproductive consequences, such as miscarriage.
Humans can be exposed to trihalomethanes by swallowing water and taking showers, among other activities.
The review notes, however, that it’s very difficult to create a direct link between trihalomethanes and health issues.
Still, health researchers have reason to be concerned about trihalomethanes, according to Philip Singer, an emeritus professor of environment sciences and engineering at UNC-Chapel Hill and an expert on the topic. According to Singer, one class of trihalomethanes is particularly worrisome: those that contain bromide.
Brominated trihalomethanes can only form when bromide is present in water. So how does bromide get there?
Where bromide comes from
Bromide is naturally present in saltwater. Because of that, coastal communities can struggle with high levels of brominated trihalomethanes, as saltwater intrudes on the freshwater that cities use for drinking water.
So for Eden, in the north-center of the state, ocean water wasn’t to blame.
“We were seeing it in the effluent coming out of the power plant up in Belews Creek,” said Terry Shelton, the director of public utilities for Eden.
Shelton was referring to Duke’s Belews Creek Steam Station, a coal-fired power plant upstream from Eden. Belews Creek relies on a large-scale “scrubber” system to trap air pollutants, such as sulfur dioxide and mercury, that otherwise would be released into the air. Scrubbers also capture bromide.
Those scrubber systems produce pollutant-laden wastewater. Duke treats the wastewater, but the treatment does not remove bromide. Then the wastewater gets released into waterways, a process that’s legally permitted under state and federal law.
“Scrubbers were required for us to install to make sure we could meet our air-emissions limits” set by the EPA, said Erin Culbert, a spokeswoman for Duke. “Now I think the industry is learning that there may be some consequences to that.”
Effects across the state
It’s not clear how many water plants might be affected by Duke’s scrubbers, which are installed at all of its active coal plants in North Carolina.
“We know that coal-fired plants with [scrubber] systems is one of the bromide sources,” Susan Massengale, a spokeswoman at the N.C. Department of Environment and Natural Resources, wrote in an email. “I don’t think that [the Division of Water Resources] has yet made a comprehensive evaluation of all the bromide sources.”
Sarah Young, another DENR spokeswoman, said the department has not seen an increase in violations for brominated trihalomethanes.
She did note that utilities on the Cape Fear River have seen elevated bromide levels in the river.
In that case, however, Duke may not be to blame. Other industries may be releasing bromide into the Cape Fear, according to Detlef Knappe, a professor at NC State University who is studying the issue.
“The main point here is, it’s not only coal-fired power plants or power plants in general that could be a source of bromide,” Knappe said in a 2014 interview with North Carolina Health News.
Additionally, the formation of trihalomethanes can be influenced by a number of factors, including the water’s temperature and pH.
Combined, placing blame on Duke could be a challenge for other water utilities.
“It’s very difficult to be able to assign a certain percentage and say, ‘Look, x percent of this has been driven by upstream plant operations,’” Culbert said.
Duke is not legally bound to limit its release of bromide. Nor are regulators and scientists sure what concentration of bromide may cause problems.
“It may be system specific,” said Tom Boyd, an environmental specialist at DENR who works with drinking-water plants.
Still, Duke is funding research that could offer a path toward reducing its release of bromide. With Duke’s funding, UNC-Charlotte civil engineering professor Vincent Ogunro is developing a system that could turn scrubber wastewater into a water-proof solid, one that wouldn’t leach pollutants.
Ogunro said it’s too early to know when such a system could be deployed at coal plants, or whether such a system would be economical for Duke.
“Research takes time,” he said.
Duke has also begun the process to identify and reach out to other potentially affected drinking-water plants, according to Culbert.
In the meantime, it has agreed to pay Eden up to $2.3 million, which will cover the costs of a treatment-system upgrade that should reduce the problems with trihalomethanes.
“They have pretty much covered any and all of the expenses we’ve had in regard to testing or sampling, all of the things that have gone into putting the project together and getting it this far along,” said Shelton of Eden’s water utility.
Shelton said that he’s been satisfied by the process of working with Duke.
“I think it’s been reasonably amicable,” he said. “They’ve been pretty forthcoming on trying to be proactive to ensure that we stay in compliance until we can get this project finished and move on.”