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Stamp sands continue to leach mercury into Torch Lake

Lake Linden – Back when copper was king, interlinked Portage and Torch Lakes were both used as dumping grounds for massive amounts of mine rock tailings, along with unhealthy amounts of mercury, cobalt and copper that escaped smelting processes.

These days, from above, the whole area “looks pretty pristine,” said Michigan Tech marine biologist Dr. Charles Kerfoot.

But underwater, both lakes still show the signs of pollution-based degradation, Kerfoot said. And while Portage Lake is showing strong signs of ecological recovery, Torch Lake’s levels of mercury, the metal most directly linked to human illness, continue to be a concern.

“In Torch Lake, mercury is continuing to go up,” said Kerfoot. “We’re worried about fish being healthy.”

Kerfoot presented the results of a study he and colleagues completed at the Torch Lake Water Quality Meeting hosted by the Houghton-Keweenaw Conservation District on Wednesday.

There’s some mercury in almost all lake water, Kerfoot said, and Upper Pensinsula lakes average about 20 percent more than downstate lakes. But during the mining era that ran from around 1875 to 1938, “we had 1,000 times more mercury coming down into the lakes” than from today’s airborne pollutants, he said.

Portage Lake appears to have largely contained that mercury under layers of new sediment, but Torch Lake sedimentation cannot keep up with mercury that appears to be leaching to the surface from the deep stamp sands – the mine tailings – below.

“A core sample from Portage has pretty bands, from the mining era, but they cover only about 30 centimeters of a two-meter core,” Kerfoot said. “That shows it’s limited.”

Torch Lake, however, has yet to rebuild its benthos layer, the area of underwater topsoil, plants that grow on it and other organisms that congregate. That means it cannott help itself rebuild soil with decaying biomass, or provide bottom-of-the-food-chain nutrition for fish and other species.

An underlying cause, Kerfoot said, is there is little new sediment being flushed into the lake.

“There’s just the Trap Rock river and three little streams,” said Kerfoot. Based on those streams’ sedimentation, he said, researchers are now estimating it will take Torch Lake over 600 years to reach acceptable mercury levels.

Kerfoot said the federal Environmental Protection Agency hasn’t been much help yet with the issue, though the Michigan Department of Environmental Quality is trying to find funds for some type of cleanup.

One suggestion involves artificially capping the underwater lake bed to prevent further mercury leaching, he said.

During a question-and-answer period, an audience member pointed out another Torch Lake issue, high levels of known-carcinogen PCBs that have been linked to numerous barrels dumped in Torch Lake, which evidence suggests have largely broken open.

In the past, PCBs were used widely to insulate electric transformers, and researchers have suggested the barrels may have been deep-sixed when a mine-related power plant shut down and was dismantled.

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