Duke Energy, in agreement with the US Fish and Wildlife Service, North Carolina Department of Environment and Natural Resources and Virginia Department of Environmental Quality, announced Monday that it will pay all cleanup costs associated with the recent Dan River spill.

The agreement requires Duke to pay any "reasonable" cost as a result of the Feb. 2 spill at its power plant near Eden, N.C., which coated 70 miles of the river in toxic coal ash, the Associated Press (AP) reported. A similar agreement was signed by Duke with the US Environmental Protection Agency last month.

"This agreement represents a significant milestone in Duke Energy's ongoing efforts to restore and monitor the Dan River and surrounding environment," the company said in a written statement. "Duke Energy is fully committed to the river's long-term health and well-being."

Duke - the nation's largest electricity company - has already been hard at work dredging up the gray sludge that has since settled at the bottom of the river as far downstream as Danville, Va. Due to unforeseen costs and unpredictable long-term effects on the river's aquatic life, new laws also require Duke to pay for ongoing monitoring conducted by government agencies. There is no set cap on the company's required expenses.

Environment and wildlife officials, such as N.C. Department of Environment and Natural Resources spokeswoman Susan Massengale, say that the agreement provides "a process that attempts to avoid lawsuits by the parties," according to the AP, but does not bar the states from filing suit if the company does not uphold its commitments.

Researchers revealed after analyzing water samples recently that the level of contamination reduced quickly after the spill took place because ash and toxic heavy metals sank to the bottom.

"This is an important step in the process of returning, as closely as possible, the Dan River to the condition it was before the spill," Massengale added.

However, rainstorms can churn up these contaminated sediments back into the water.

In April, the conglomerate reportedly spent $15 million on containing the spill and immediate aftermath, and warned lawmakers that it could cost them - or their electricity customers, rather - as much as $10 billion if it is forced to remove its ash at all 14 contaminated sites in North Carolina.