The Coeur d’Alene River ran hard and muddy Tuesday in Rose Lake, engulfing beaches, claiming low-lying fields and pushing deep into the floodplain.
But the churning waters created ideal conditions for scientists studying how heavy metals move through the river system and into Lake Coeur d’Alene. Three contractors for the U.S. Environmental Protection Agency spent the day chasing the pulse of water downstream, collecting sediment samples along the way.
“Cranking, cranking, cranking,” Craig Sauer, a hydrologist for CH2M Hill, told his co-worker Nathan Williams, as Williams reeled in a water-sampling unit with a hand crank.
The torpedo-shaped unit held about three liters of water. The sample was taken from the bridge at Rose Lake, where the river was cresting late Tuesday morning. Based on a formula that incorporated water velocity, Williams raised the unit at a steady rate of 2 feet per second, to ensure he got a representative sample from the 55-foot-deep water under the bridge.
EPA officials assembled the sampling team after Sunday night’s heavy rains. With river flows peaking at 28,000 cubic feet per second Monday evening at Cataldo, they knew there would be good sampling opportunities as floodwaters moved downstream.
High flows scour the river bottom, releasing sediments that contain heavy metals from historic mining activity in the Coeur d’Alene Basin.
“Even though that water looks benign, it’s carrying high levels of lead,” said Ed Moreen, an EPA project manager.
Based on past sampling, Moreen would expect the floodwaters to contain lead levels of up to 6,000 parts per million. The cleanup standard in the basin is 700 parts per million for lead, a neurotoxin.
Results from Tuesday’s sampling will be available in several weeks.
Each year, about 390 tons of lead washes out of the Coeur d’Alene River at Harrison and ends up in Lake Coeur d’Alene. Most of the lead sinks to the bottom, where it doesn’t pose an immediate threat to human health. But it is a concern for fish and other wildlife, and it could become a human health threat if the lake’s chemistry were disrupted and the lead were resuspended in the water.
Most of the lead that gets flushed into the lake comes from 37 miles of the Coeur d’Alene River between Enaville and Harrison. Last fall, the EPA spent $250,000 sampling river sediments to map the hot spots for heavy metals. Knowing how floodwaters transport the metals is another piece of the modeling effort, which will eventually result in a cleanup plan for the Lower Coeur d’Alene River and its interconnected marshes and lakes, Moreen said.
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