A long-delayed risk study for a Montana mining town where hundreds have died from asbestos exposure concludes that even a minuscule amount of the substance can lead to lung problems.

The 328-page document released Monday will determine when work can end on the cleanup of asbestos dust from a W.R. Grace & Co. vermiculite mine outside Libby.

Cleanup efforts in the scenic mountain town that's become synonymous with asbestos dangers already have addressed more than 2,000 homes and businesses, at a cost of roughly $500 million.

Despite Libby's many deaths, the Environmental Protection Agency is using a less-drastic benchmark, lung scarring, to help determine how much asbestos poses a risk.

W.R. Grace and industry groups have criticized the EPA's low threshold for exposure as unjustified and impossible to attain.