Charlotte Water: Contaminants detected, but water is safe

Chemicals used by Duke Energy to curb air pollution appear to have caused a spike in contaminants in Charlotte’s drinking water.

Charlotte Water reported Thursday elevated levels of disinfection byproducts called trihalomethanes. THMs may cause liver, kidney or central nervous system problems and may increase cancer risks.

The levels detected came close to federal and state limits but do not make the water unsafe, authorities said.

THM levels in drinking water began to rise in mid-2014. The compounds are more likely to form as water warms.

But it was also about a year after Duke began using calcium bromide, in 2013, to wash coal at its Marshall and Allen power plants on lakes Norman and Wylie. The bromide wash reduced releases of toxic mercury into the air when coal is burned.

Bromide reacts with chlorine, which is used to disinfect drinking water, to form THMs.

“It appears that may have been the triggering event,” Duke spokeswoman Erin Culbert told reporters Thursday.

Duke stopped using calcium bromide at the plants in May, but the region’s drought has kept it from being flushed out of the lakes. That’s expected to improve when rainfall returns and water cools this fall.

Duke acknowledged earlier this year that bromide releases from power plants could cause THM problems in water systems downstream.

In a $102 million settlement of federal charges over coal ash contamination, Duke agreed to set up a claims process for water utilities that felt harmed by bromide released by power plant scrubbers, which also clean air emissions.

Duke had already paid two cities that draw water downstream of its Belews Creek power plant, Eden and Madison, $2.3 million and $770,000 respectively to modify their treatment systems.

Other factors can also form THMs, including warm, still water. Charlotte Water director Barry Gullet said the city will change treatment processes and operating practices, such as flushing hydrants more often and reducing the pH of water, to reduce those risks.

Those changes could cost $1 million to $1.5 million, Gullet said. It’s unclear whether the city will seek reimbursement from Duke.

“We know, and Duke agrees, that at least some of this is coming from the Duke plant,” Gullet said.

Gullet said York, S.C., has also seen high THM levels. Officials there could not be reached Thursday.

The utility’s announcement Thursday was triggered by results this week that found high THMs at eight of 12 sampling sites on the fringes of the city.

Individual readings ranged as high as 116 parts per billion, well above the federal standard of 80 ppb. Because results are averaged over time, none constituted a violation of the Safe Drinking Water Act.

Customers at the sampling sites – mostly businesses or county buildings – were notified of the results Thursday.

“It would take someone ingesting large, large amounts over 20 to 30 years to get the same effects found in (lab) animals,” said Dr. Stephen Keener, the Mecklenburg County Health Department’s medical director. “We feel very comfortable in reassuring citizens that use the water that this is not a situation that causes concern.”

This story was originally published August 13, 2015 at 3:19 PM with the headline "Charlotte Water: Contaminants detected, but water is safe."