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Toxic Dunes Mapped in Coeur d'Alene River Bottom

Posted by Susan Drumheller at Dec 13, 2012 10:00 AM |

Although the Coeur d'Alene Basin's mining legacy has been studied for decades, scientists are still learning new things that will eventually help remedy the metals contamination.

Toxic Dunes Mapped in Coeur d'Alene River Bottom

Trail of the Coeur d'Alenes threads through the Coeur d'Alene Basin. Idaho Scenic Byways photo.

As the Environmental Protection Agency, its partners and contractors embark on the Upper Coeur d'Alene Basin cleanup action plan, teams of scientists, government staff and stakeholders are taking hard look at how to deal with the downstream impacts of a 100 years of mining.

And it's becoming clearer that it might not be necessary to have every mine and tailings pile mopped up in the Upper Basin before serious work can begin on the toxic legacy of mining that's washed downstream to the Lower Basin.

The Upper Basin is defined generally as the area upstream of the confluence of the North Fork and South Fork of the Coeur d'Alene River. Everything below, from Cataldo on down to Lake Coeur d'Alene, is considered the Lower Basin.

Some of the contamination levels in the downstream reach of the river are shockingly high, and every year migrating waterfowl drop dead during their stopover to feed in the vast wetlands of the Lower Basin.

Semiannual flooding further flushes contaminants into the wetlands and requires land managers to hose down boat launches and other recreation sites to make them safe for human use.

Scientists have been studying how the metals move through the Lower Basin, and here are a few interesting facts they shared at a recent meeting of the Lower Basin Project Focus Team:

  • The average amount of lead moving through the Lower Basin and emptying into Lake Coeur d'Alene each year is 393 tons
  • Only 10% of that load is from Upper Basin, while 5% comes from eroding river banks
  • The vast majority of the metals—85%—are from the river bed in the Lower Basin itself
  • The lower you go in the river, the higher the lead concentration gets.

Scientists are using high-tech bathymetry to map the river bottom, and observe how lead-contaminated dunes move downstream along the riverbed. This information will be used to design pilot projects in the next year or two to help guide a longer term clean-up plan.


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