Study Measures Flow Of Mine Waste Epa Finds Heavy Spring Flooding Not Needed To Flush Pollutants

Researchers have confirmed their suspicion that a muddy springtime plume cruising across Lake Coeur d’Alene carries Silver Valley mining pollution to Spokane.

The 30-foot-deep plume carried one-third of the lead it picked up from the Coeur d’Alene River into the Spokane River, according to the U.S. Geological Survey.

The data was released at an Environmental Protection Agency technical workshop last week.

With lead and other toxic metals showing up at potentially harmful levels along Spokane River beaches, the discovery that metals flow down-river from the Coeur d’Alene isn’t exactly earth-shaking.

“It confirms what common sense has told us all along,” said Bob Bostwick, press secretary for the Coeur d’Alene Tribe, involved in an 8-year-old lawsuit against Silver Valley mines.

But Paul Woods, the lead USGS researcher, said this summer’s data showed that metals move in the annual spring runoff plume surprisingly often.

Until now, scientists assumed only unusually heavy spring floods could push the plume across the lake. But this spring, runoff flowed from the mountains at rates seen every two or three years, Woods said.

Field crews spent two days in early June on the water, taking samples at eight sites including the mouth of the St. Joe River, where heavy metals are practically nonexistent. Data crunchers then figured out what the plume contained, including levels of lead, zinc and cadmium.

Lead showed up at 30 micrograms per liter at the mouth of the Coeur d’Alene near Harrison. Lead levels dropped during the trip across the lake due to metals falling out of the plume, dilution from the St. Joe and scientific error, Woods said.

At the outlet of Lake Coeur d’Alene into the Spokane River, lead still measured 10.5 micrograms per liter. A microgram is a millionth of a gram; a liter is a little more than a quart. Lead can cause mental and physical retardation, especially in young children.

A mining spokeswoman downplayed the importance of the findings. The amount of metals in the plume essentially matches EPA data already available, said Holly Houston, executive director of the Mining Information Office.

“I don’t see these numbers as different from everything we’ve seen before,” Houston said. “By the time they get to the outlet, you can see (lead) drops significantly, showing the majority settles out in the lake which is what people have been talking about.”

The amount of lead found flowing into the Spokane River is within the 15 mg/l drinking water standards set at the tap, she said.

But Bostwick said the data underscores the need to get rid of mining pollution upstream.

“The damage from this is going to go on forever if it’s not cleaned up,” he said. “If you clean it up, you stop that plume.”