The Spokesman-Review reported that the $250,000 mapping project started this month and will involve hundreds of sediment samples.
The agency said the samples will help officials locate lead hot spots and where the river bottom is highly erodible. Ed Moreen, remedial project manager for the agency, said the information will be used to design projects targeting the worst pockets of lead.
Each year about 390 tons of lead from past mining operations washes out of the river at Harrison and into Lake Coeur d'Alene. That's enough to fill about 22 dump trucks.
"Eighty-five percent of the lead that shows up at Harrison is coming from this riverbed," said Moreen.
Jamie Brunner of the Idaho Department of Environmental Quality said most of the lead sinks to the bottom of the lake. She said swimmers are at a low risk of ingesting harmful levels of lead.
The lead comes from upstream mines where companies, before modern pollution laws took effect, dumped mining waste into the river. The lead over decades has spread out in the flood plain. Each spring migrating tundra swans die from ingesting lead that has ended up in marshes along the river.
Moreen said sediment samples show the pollution is layered 4 to 5 feet deep through the riverbed. Samples from pre-mining days have lead levels of 50 to 70 parts per million, but areas with mining waste have lead concentrations of 60,000 parts per million.
Money for the work is coming from a $263 million settlement with Hecla Mining Co. The company agreed to the settlement two years ago.
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