Federal officials anticipate finishing by late 2014 a risk study to guide the cleanup of an asbestos-contaminated Montana mining town, after a panel of scientists backed draft results that say even a minuscule amount of the substance can lead to lung problems.

The long-awaited document will determine when work can end on the cleanup of asbestos dust from a W.R. Grace & Co. vermiculite mine outside Libby, Mont. Hundreds of people in and around Libby have died from exposure, and many more have been sickened.

The cleanup so far has cost more than $447 million since it started in 1999.

Environmental Protection Agency toxicologist Deborah McKean says the agency will complete its risk study earlier if it can, possibly by the end of this year.

But she says the EPA first must do additional work recently recommended by its Science Advisory Board, a group of outside scientists that spent more than a year deliberating the agency’s preliminary findings.

Meanwhile, the cleanup grinds on. At least 80 and up to 100 properties in town are queued up for work this year, said EPA project manager Rebecca Thomas.

Several hundred properties still need to be addressed, and that list could grow significantly depending on the outcome of the risk study.

Work on the mine site outside town has barely begun. It closed in 1990 and remains the responsibility of W.R. Grace.

Despite Libby’s many deaths, the science board said the EPA was right to use a less-drastic benchmark, lung scarring, to determine how much asbestos poses a risk.

That could have implications far beyond the town itself. Dozens of sites across the U.S. received or processed vermiculite from Libby’s mine, which was used as insulation in millions of homes across the U.S.

The science board also said the agency should gather more data to back up its position.

W.R. Grace and industry groups have criticized the EPA’s proposal for a strict new standard as unjustified and impossible to attain. The agency has not yet formally responded to those comments.

EPA toxicologist Deborah McKean said she did not expect a significant change to the agency’s determination that exceeding extremely low levels of airborne asbestos — 0.00002 fibers of the mineral per cubic centimeter — raises the risk of lung-scarring.

“They are asking us to bolster our decision,” McKean said. She added that final exposure standards won’t be established until additional work is done.

It will take another six months after that for the study to be completed, she said.

The town remains under a first-of-its kind public health emergency declaration issued by Environmental Protection Agency administrator Lisa Jackson in 2009. The deaths are expected to continue for decades due to the long latency of asbestos-related diseases.