Federal officials say their final analysis of a Northwest Montana community wracked by deadly asbestos contamination shows a costly and much-criticized cleanup is working, even though some 700 properties have yet to be investigated and concerns linger over asbestos left behind.

The U.S. Environmental Protection Agency has spent more than $540 million removing asbestos in and around the town of Libby. The material came from a W.R. Grace and Co. vermiculite mine that is now closed.

Health workers say as many as 400 people have died and almost 3,000 have been sickened from exposure.

Yet after a lengthy review of the health risks, the EPA said in a report issued Friday that people could continue to live in Libby and neighboring Troy without excessive exposure.

“EPA’s indoor and outdoor cleanups have significantly reduced risk from exposure to asbestos,” agency officials said in a Friday statement.

An EPA research panel concluded last year that breathing in even a tiny amount of asbestos from Libby could scar lungs and cause other health problems.

Critics of the cleanup point out that asbestos would be left in the walls of houses, underground and elsewhere — areas that the EPA says pose less of a chance of exposure. Some Libby residents said the asbestos inevitably will escape during future excavation work, home renovations and accidents such as fires.

State officials have raised similar concerns.

The EPA acknowledged in Friday’s analysis that higher levels of asbestos could be found in the 700 properties they have not been able to access because of uncooperative owners.

Vermiculite from the Grace mine was used as insulation in millions of houses across the U.S.

In the Libby area, asbestos-tainted mine waste unwittingly was used as a garden-soil additive by residents and as fill for the local construction industry.

The government so far has removed more than a million cubic yards of dirt and contaminated building materials from more than 2,000 properties in Libby and Troy.

EPA officials have never fully documented how many homes and businesses were left with vermiculite in their walls after cleanup work was completed.