A pipe from the Dan River Power Plant where coal ash spilled is seen along the Dan River in Eden, N.C., in this Feb. 5, 2014, file photo.

RALEIGH, N.C. - Duke Energy has completed removal of large pockets of coal ash from the Dan River months after a massive spill at a North Carolina power plant, federal environmental officials said Thursday.

The U.S. Environmental Protection Agency's on-scene coordinator, Myles Bartos, said Duke had dredged up about 2,500 tons of ash and contaminated sediment that settled against a dam in Danville, Virginia. Another 500 tons was recovered from other pockets in the river and settling tanks at two municipal water treatment plants in Virginia.

Coal ash contains an array of such toxic heavy metals as arsenic, mercury and selenium.

Duke estimates about 39,000 tons of coal ash spewed into the Dan after a drainage pipe collapsed Feb. 2 at a waste dump in Eden, turning the river gray for more than 70 miles. Bartos said the cleanup is considered complete, though Duke has recovered only a fraction of the total spilled.

Bartos said recent testing of both the river water and bottom sediment has shown concentrations of toxic metals below federal limits and close to what was likely present before the spill. State and federal agencies will continue to monitor the environmental health of the river.

Bartos said if more large deposits of contamination are later discovered, Duke will be required to remove them.

"We continue to do some monitoring and will base our decisions for actions on the data collected," Bartos said. "But I don't think there will ever be a removal again in the river. I think it has been adequately removed."

Headquartered in Charlotte, Duke is the nation's largest electricity company. In past statements to investors, executives have said they do not expect costs incurred from the cleanup effort to be large enough to affect the $50 billion company's profitability.

Duke spokesman Jeff Brooks stressed that even though the cleanup effort is complete, the company is still in the early stages of developing a study with the U.S. Fish and Wildlife Service to track the long-term impact of the spill on aquatic life.

"This is just one aspect of our response," Brooks said. "We're not going away from the Dan River, and we continue to be committed to the communities along the Dan River. We'll be there for the future, and we'll work to keep the Dan River moving forward and remaining healthy."

Environmental watchdog groups pointed out Thursday that Duke recovered less than 10 percent of the coal ash it spilled. They said the contamination still poses a threat, especially at times when the river flow is high and bottom sedimembient churns up into the water.

"Where did it all go?" asked Frank Holleman, a senior attorney with the Southern Environmental Law Center. "They have not finished the cleanup. They just stopped."