In 1908 a massive flood washed millions of cubic yards of toxic mine wastes into the Clark Fork River system. Generations later, in 1983, the Milltown Reservoir was listed by the Environmental Protection Agency as a Superfund site after the discovery that several million cubic yards of heavy metal contaminated sediments had piled up behind the dam, polluting the groundwater beneath with high concentrations of arsenic.
While the Anaconda Copper Mining Company was responsible for the problem, its successors, the Atlantic Richfield Company and British Petroleum, along with the dam's owner Northwestern Energy, have legal liability for the cleanup today. The Superfund work is led by the EPA and the state DEQ while the work itself is carried out by the Missoula-based Envirocon, a subsidiary of the Washington Corporation.
The main project goal is to reclaim the Milltown aquifer by removing the contaminated sediments and reservoir above it. To do that, the Milltown Dam was removed and the worst of the sediments have been excavated and shipped to an existing repository at the Anaconda Superfund Site.
The Montana Natural Resource Program then takes over to implement its restoration plan that will create a new river channel and revegetated floodplain for the Clark Fork River.
The restored confluence area will be subsequently redeveloped as a public park with restored fish and wildlife habitat, trails, river access sites and interpretive displays.