Duke Energy says new estimates reduce the amount of coal ash that spilled into the Dan River last week to 30,000 tons to 39,000 tons.
Duke had initially estimated that 50,000 tons to 82,000 tons of ash went into the river when a stormwater pipe broke under an ash pond Feb. 2 at its retired Dan River power plant in Eden.
Surveyors used computer models of the pond after the incident to come up with the new estimate, Duke officials said.
The new numbers mean less than 4 percent of the ash in the pond spilled, Duke says.
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After finally plugging the broken stormwater pipe, ending its leak into the river, Duke turned its attention this week to vacuuming up a 250 cubic yard deposit of ash from the river just downstream of the spill.
The Environmental Protection Agency said its attention is now turning to environmental damage assessments and the cleanup of ash in the river.