The owner of a former vermiculite mine in northwestern Montana that spread harmful asbestos in and around the town of Libby has offered $18.5 million to settle the last of the state’s claims for environmental damages, Gov. Greg Gianforte announced Tuesday.

The proposed settlement was filed in W.R. Grace & Co.’s bankruptcy case in Delaware for the Libby Asbestos Superfund Site in Lincoln County.

Asbestos from a vermiculite mine owned by W.R. Grace beginning in 1963 polluted the area until the mine was shuttered in 1990. Cleanup began in 2000, after media reports spurred federal officials to investigate widespread health problems among area residents.

Microscopic asbestos fibers can cause lung problems and eventually death. Health officials estimate that several thousand people have been sickened in northwest Montana from exposure to Libby’s asbestos and at least 400 have died.

More than 2,600 homes, businesses and other properties were cleaned up at a cost of more than $600 million under the U.S. Environmental Protection Agency’s Superfund program for hazardous sites. W.R. Grace agreed in a 2008 settlement to pay the EPA $250 million for cleanup work.

“After years of negotiation following Grace’s historic damage, Libby and communities in Lincoln County can more fully recover,” Gianforte said in a statement. “I look forward to the positive impact this settlement can bring to the people of Libby and Lincoln County.”

W.R. Grace noted the settlement requires public review and court approval. The state is taking public comment through Feb. 13.

“This settlement is part of our ongoing commitment to constructively work with the Libby community, the state of Montana and other key stakeholders,” W.R. Grace spokesperson Sue Cardillo said in a statement.

The first $5 million would be due to the state within six months of reaching a final agreement. The additional payments, plus interest, would be made over 10 years.

The money would be used to restore, replace or rehabilitate damaged natural resources, state officials said. W.R. Grace would also provide the state with financial assurances for the operation and maintenance of an impoundment dam that holds asbestos-laden tailings from the former mine.

The $18.5 million would also settle most claims made by the state Department of Environmental Quality, but it does not affect W.R. Grace’s requirements to perform other Superfund work subject to EPA oversight.

More than 2,000 Montana residents reached settlements with the state totaling $68 million in 2011 and 2017 for failing to warn them about the dangers of asbestos exposure.

In February 2022, a jury awarded an Oregon man $36.5 million in a lawsuit against W.R. Grace’s workers compensation insurer from 1963-1973 because the company did not warn workers of those dangers. Hundreds of others have filed lawsuits and claims.