As crews continued Wednesday to try to stop the flow from a leaking Duke Energy ash pond in Eden, the company announced a surprising discovery.
The stormwater pipe that broke Sunday under the 27-acre pond was made of corrugated metal, not the reinforced concrete that Duke had believed it to be.
The discovery underscores how much remains unknown about what caused a break that washed 50,000 to 82,000 tons of ash down the Dan River with at least 24 million gallons of water.
Duke also reported that its own tests found trace metals, the potentially toxic elements of ash, in river water. The company said no samples that were filtered, as municipal water systems do, exceeded state drinking-water standards.
Duke is sampling water daily at points from upstream of its power plant to South Boston, Va., downstream. The samples include water at municipal intakes and were analyzed at Dukes lab in Huntersville.
Danville, Va., which has the closest intake to the Duke power plant, has said it is able to filter out contaminants from the gray-tinted river water.
The test results are not surprising, because this is the same message weve had for closing these ash basins its just not water soluble, said Jason Allen, Dukes senior vice president for environmental health and safety. Metals are not easily dislodged from ash particles in a river or lake, he said, and the particles will settle to the bottom.
The N.C. Department of Environment and Natural Resources said it also expects to release water sampling results this week. Duke reported the flow of ash and water to the river has significantly decreased since the spill began, according to a DENR news release.
Duke officials had said Tuesday that it was definitely unexpected that a reinforced concrete pipe would break.
But crews unearthing the pipe learned that two-thirds of its length including the break point is corrugated metal, while the third closest to the river is reinforced concrete, Duke spokeswoman Erin Culbert said Wednesday.
Knowing the material helps inform the engineers who are designing a permanent solution, she said. Its still not clear what caused the pipe to break, she said.
The pipe was installed in the 1960s, Duke said, before the ash pond was expanded and divided into two basins. The primary basin held 992,000 tons of ash, meaning that 5 percent to 8 percent of it was released.
A 2009 engineering report on the ash pond dam, filed with the Environmental Protection Agency, noted the 48-inch pipe and a second 36-inch pipe under the basins.
The report said the pipes should be monitored for turbid stormwater, which would indicate soil leaking into them, but did not depict them as hazards. It said Duke inspects the pipes monthly; on Tuesday, Duke said the broken pipes discharge end had been inspected Friday.
Duke says the Dan River has the only ash ponds in North Carolina with such pipes beneath them.
Culbert said at midday Wednesday that the flow from the pipe into the Dan has decreased but is still entering the river. She did not have an estimate of its volume.
Donna Lisenby of the advocacy group Waterkeeper Alliance paddled the river late Tuesday afternoon and estimated the flow was 5 to 6 inches high in the 48-inch pipe.
Advocacy groups have criticized Duke for not publicly reporting the spill until a day after it was discovered, but the N.C. Department of Environment and Natural Resources said Duke obeyed state law.
State law says wastewater discharge permit holders, including Dukes Dan River power plant, have to report to the department any events that potentially threaten public health or the environment. Permit holders have 24 hours to report from the time they become aware of the event.
Duke has said the pipe break was discovered about 2 p.m. Sunday. The company said it reported the spill to the environment department about 6:30 p.m. Sunday.
State law also requires the owners of wastewater facilities to issue a news release within 48 hours of discharging 1,000 gallons or more to surface waters. Dukes news release on the spill was filed at 4 p.m. Monday, about 26 hours after its discovery.
Henderson: 704-358-5051; Twitter: @bhender