SALISBURY — The threat of a lawsuit by environmental groups resulted in the release last week of Duke Energy maps that show the Yadkin River could be inundated with coal ash in the event of a major dam failure.

Maps specifically show that within 35 minutes, a dam failure at Buck Steam Station’s largest coal ash pond could inundate a section of the river from Interstate 85 to the first bend in the river. A breach of the dam adjacent to Buck Steam Station’s secondary ponds would cover the same area in about 10 minutes and dump a lower amount of coal ash — the byproduct of burning coal for energy — into the Yadkin River, said company spokeswoman Erin Culbert.

Although the Environmental Protection Agency required that the maps be released in April, Duke Energy did not publicly release the documents until Friday. Culbert said the delay is a result of the company’s intent to protect details of “critical infrastructure.” She said the company decided to release the maps after examining practices of other energy providers.

Culbert said Rowan County’s first responders are well informed about potential dangers.

“We do make sure that we have an ongoing dialogue at each of our sites, including an annual face-to-face meeting,” she said.

County Emergency Services Chief Frank Thomason confirmed Culbert’s assessment.

“They do reach out to us, and we do have access to their plans,” Thomason said. “For years, we’ve been on all their emergency response plans.”

When pushing for the public release of inundation maps, Southern Environmental Law Center attorney Frank Holleman said communities would learn how much they could be devastated by “coal ash and toxic water pollution if Duke Energy’s dangerous coal ash storage sites fail.”

While dam failures at coal ash sites could affect hundreds of individual structures, none of those sites are located immediately adjacent to Buck Steam Station.

Yadkin Riverkeeper Will Scott said a failure at Buck Steam Station could allow coal ash to release harmful metals into the river and have negative effects on wildlife.

The Yadkin Riverkeeper was not among the groups threatening to sue Duke Energy, but Scott said he is glad to see the release of the maps.

The maps do not show the inundation area extending beyond the first bend in the Yadkin River after Buck Steam Station. Culbert conceded that coal ash could spread farther down the Yadkin River but said the depth of any coal ash would be shallower than the immediate inundation area.

“These are planning models and represent the worst-case scenario, but they do not represent the most likely scenario,” she said.

Culbert said Duke Energy employees, in many scenarios, would be able to react to problems before a major failure, which may not involve dams. In the case of the 2014 Dan River spill, a pipe broke and resulted in the release of tens of thousands of tons of coal ash and millions of gallons of pond water. The material traveled 70 miles downstream.

In addition to others, Duke Energy faced a fine for not maintaining the Dan River site to minimize the risk of a spill.

Asked about Duke Energy’s emergency plans and inundation maps, Thomason said he has adequate information to respond in case of a major failure.

Once Duke Energy excavates Buck Steam Station’s coal ash ponds — required by a settlement between the company and Yadkin Riverkeeper — they would be eliminated, Culbert said. The company must dig up coal ash at Buck Steam Station, recycle it or place it in a lined landfill that’s separated from groundwater.

Contact Josh Bergeron at 704-797-4246.