Flooding spiked lead levels in Lake Coeur d’Alene
January rain, snow carried mine pollution into lake
An estimated 352,000 pounds of lead washed into Lake Coeur d’Alene on Jan. 18 after flooding related to a rain-on-snow event.
That’s the weight equivalent of 70 Dodge Ram 1500 pickups – and the highest volume of lead recorded in a 24-hour period since major flooding in February 1996.
Greg Clark, a U.S. Geological Survey hydrologist, attributed high lead concentrations to a rapid rise in the Coeur d’Alene River caused by pounding rains and melting snow. At Harrison, where the river empties into Lake Coeur d’Alene, the Jan. 18 flows averaged 19,000 cubic feet per second.
“We haven’t seen those kinds of flows in quite a while,” said Clark, associate director of the Idaho Water Science Center in Boise. “We end up with a lot of metals – lead in particular – transported to the lake during those types of events.”
The lead is the legacy of 140 years of hard-rock mining in the Coeur d’Alene River’s headwaters. Government officials said the January data demonstrates the complexity of mine Superfund cleanup.
“There’s so much lead in that upper basin,” said Ed Moreen, a program manager for the U.S. Environmental Protection Agency. “It’s going to continue to get picked up and redistributed into Lake Coeur d’Alene until we can do something about it.”
Most of the lead from January’s high flows settled at the lake’s bottom, which acts as a sink for heavy metals. USGS monitoring detected low lead levels at Lake Coeur d’Alene’s outflow to the Spokane River.
As part of a lake management plan, scientists with the Idaho Department of Environmental Quality and the Coeur d’Alene Tribe are studying the behavior of lead and other metals at the lake bottom. The EPA is also working on a cleanup for the upper Coeur d’Alene basin to reduce the volume of heavy metals flowing downstream.
Occasionally, lead levels in Lake Coeur d’Alene exceed federal drinking water standards of 15 parts per billion, said Glen Rothrock, DEQ coordinator for the lake management plan. However, those levels typically occur during spring runoff when the water is too cold to swim in, he said.
During summer months, Rothrock said it would be rare for swimmers to ingest lead at levels posing human health risks. Testing shows summer lead levels in the lake at 2 to 3 parts per billion.
Unlike zinc, which dissolves in water, lead is attached to sediment. As a result, it moves down the river system in bursts, said the USGS’s Clark.
Polluted sediment flows out of the South Fork of the Coeur d’Alene River and into the river’s main stem. When the sediment reaches the slower-flowing waters of the main stem, the sediment drops to the bottom where it is stored for months or even years.
Floods, when they occur, act “almost like a flushing event,” Clark said. “We get these big events and boom! You’ve got a pulse of lead moving into the lake.”
At the peak flow on Jan. 18, water samples taken at Harrison had 3,480 micrograms of lead per liter, which is roughly 3,480 parts per billion. That’s the highest lead reading at Harrison since February 1996, when the readings were 6,500 micrograms per liter, according to USGS monitoring.
“We’ve been sampling there for over 20 years,” Clark said. “These are pretty large concentrations, way higher than they should be.”
Last summer, the EPA unveiled a proposed plan for cleaning up mining pollution in the upper Coeur d’Alene basin. It targeted more than 300 old mine sites and contaminated groundwater.
But the plan drew sharp criticism from Gov. Butch Otter, other elected officials and local residents, both for its $1.3 billion price tag and its 50- to 100-year time frame. The EPA is reviewing the public comments, with a final plan expected out later this year.
Barbara Miller, a Silver Valley activist, said January’s high water renewed her concerns about the EPA’s decision to build a repository for Superfund mine waste near the Coeur d’Alene River at Cataldo, Idaho. When the river spilled over its banks, the 18-month-old repository flooded.
“Lead exposure is very harmful to humans as well as wildlife and the environment,” Miller said. “That repository is too big of a gamble.”
But EPA’s Moreen said onsite inspectors observed the repository working as designed during January’s flooding. Interstate 90 separates the river from the repository, slowing muddy floodwaters as they move through culverts underneath the freeway, he said.
“You don’t get the scouring like you do in the middle of the river,” he said. “After the flood reaches its peak, the sediments drop out and the receding water flows back to the river.”
Moreen said the EPA conducts ongoing sediment testing along the lower Coeur d’Alene River, its floodplain and marshes. The testing will help build on knowledge about metals transport, he said.
Meanwhile, the DEQ and the Coeur d’Alene Tribe are studying heavy metals embedded in mud at the bottom of Lake Coeur d’Alene. High oxygen levels in the lake’s water and natural bacteria action act like a cap on the metals, the DEQ’s Rothrock said. Together, they keep the metals in particulate form at the lake’s bottom.
To protect Lake Coeur d’Alene’s water quality, DEQ and the tribe in 2008 adopted a lake management plan. It is focused on reducing phosphorus flowing into the lake, which spurs plant growth and reduces oxygen levels. If oxygen levels plummet, the metals could start changing into harmful dissolved forms, Rothrock said.
Dealing with more than a century of mining pollution in the Coeur d’Alene watershed is a long-term challenge, said the USGS’s Clark.
“It’s going to take a long time for all these trace metals to bleed out of the system,” he said.