Milltown Reservoir Superfund Site
The Milltown Reservoir Sediments Superfund Site is a major Superfund site in Missoula County, Montana, seven miles east of Missoula. It was added to the National Priorities List in 1983 when arsenic groundwater contamination was found in the Milltown area.
Source: Wikipedia — Milltown Reservoir Superfund Site (CC BY-SA 4.0)