RALEIGH, N.C. (AP/WNCN) – The country’s largest electric company is being ordered to excavate coal ash from all of its North Carolina power plant sites, slashing the risk of toxic chemicals leaking into water supplies but potentially adding billions of dollars to power bills.

North Carolina’s environmental agency said Monday it has decided Duke Energy Corp. must remove the residue left after decades of burning coal from six remaining sites.

The six sites are Allen, Belews, Cliffside/Rogers, Marshall, Mayo and Roxboro facilities, officials said.

Duke responded Monday afternoon saying that “excavation at some sites will take decades” and could nearly double the current $5.6 billion estimate for closing the basins.

The company had wanted to cover some storage pits with a waterproof cap, saying that would prevent rain from passing through the pits and carrying chemicals like mercury and arsenic through the unlined bottoms.

Cleanup became a priority after a 2014 leak from a Duke Energy site left coal ash coating 70 miles of the Dan River on the North Carolina-Virginia border.

By August 1, 2019, Duke Energy is required to submit final closure plans.

Here is the full text from Duke Energy: