The vermiculite was mined by Grace from a mountain outside town and shipped across the country for use as insulation, fertilizer, in fireproofing material and other commercial products.
The mine closed in 1990.
Health problems first noticed in mine workers have since become pervasive in Libby, affecting spouses who laundered their husbands' dust-covered clothes, generations of residents who played as children near Grace's processing plants and others.
In public testimony and filings with the EPA, Grace has argued that less-severe lung problems considered a sign of asbestos disease can be confused with other health problems, such as obesity. The company maintains that the science used by the EPA to craft its proposal was flawed and has urged the agency to do more research before moving forward.
The air is far cleaner in Libby today than it was when the EPA first arrived, removing thousands of truckloads of contaminated soil and replacing it with clean topsoil. But the agency has acknowledged some people in Libby are still at risk, particularly landscapers and others who stir asbestos-laden soil.
Grace reached a $250 million settlement with the EPA in 2008 to cover government cleanup costs in Libby and the surrounding area. The company remains responsible for cleaning up the mine site. Company executives accused of knowing of the health problems in the town were acquitted of federal criminal charges three years ago.
Arthur Frank, an occupational physician who has testified against Grace in asbestos litigation, said it was "disingenuous" for Grace to now argue against the EPA proposal.
"I don't even see why Grace gets a say in this matter. They're the ones that caused this disaster," said Frank, a professor at Drexel University School of Public Health in Philadelphia. "The situation in Libby specifically shows that minimal pleural disease carries with it significant physiological changes in the lungs."