BILLINGS, Mont. (AP) — The U.S. Environmental Protection has given final approval to a costly cleanup program for a Montana community where health officials say hundreds of people have died due to asbestos exposure.

The announcement on Monday came more than 15 years after cleanup work began in Libby, a mining town near the Montana-Idaho border. An EPA risk assessment last year found that the cleanup of almost 2,300 properties in Libby and nearby Troy had significantly reduced asbestos exposure risks.

Yet even with that work, contaminated material remains in the walls of many houses and about 700 properties have yet to be investigated.