For years, the EPA has agreed with mining officials that toxic sediments stuck behind the Milltown Dam on the Clark Fork River near Missoula, Mont., were best left alone. But when polluted waters escaped from the dam in February, they killed fish and energized activists, who renewed their call for the agency to remove the mine wastes.


Following the fish kill, tests by Missoula's Health Department found greatly elevated levels of copper, zinc and arsenic in the once-dammed waters. Metals in the Milltown Reservoir were accumulated during more than a century of mining and smeltering upstream, in Butte and Anaconda (HCN,10/30/95).


But EPA officials haven't changed their position. They said removing the contaminated sediment is still not worth the money, a conclusion shared by Atlantic Richfield Co., which now owns the site. Instead, the agency wants to dig monitoring wells to track the plume of pollution as it moves past the dam. The wells would signal EPA when to tell people their drinking water was becoming contaminated.


* Mark Matthews