Milltown’s aquifer is polluted with arsenic as a result of tainted mine tailings that have built up behind the reservoir over the decades. The move by EPA comes after years of lobbying by local residents, and is approved by county leaders.

NorthWestern, owner of the dam, and Atlantic Richfield Co. will pay for a US$100M cleanup. EPA estimates the operation – which will see the 2.4Mm3 of contaminated sediment transported 161km upriver to tailings ponds – will be completed within seven years.

Demolition is due to begin in early 2006. The removal of the structure will make way for a bypass channel in the Clark Fork river, allowing the Clark Fork and Blackfoot rivers to flow freely for the first time since Milltown dam’s construction in 1907.

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