The Southern Environmental Law Center said in a news release that Duke reported in December it has removed more than 650,000 tons of the 3.6 million tons of ash at the W.S. Lee facility near Williamston.
The utility has nine more years to removing the remaining 85 percent of the ash from the site as part of a settlement with the environmental group.
Conservationists say the ash pits at the Anderson County site were especially dangerous because they did not have a liner and were so close to the Saluda River.
Duke Energy will also remove coal ash from a plant in Darlington.