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Machine may pull mercury from lake

It could be a breakthrough and it might be a bust, but Nevada Irrigation District officials are hoping a new mercury removal process for Combie Reservoir will be revolutionary for Northern California streams and lakes.

Like many bodies of water in the area, the reservoir and the Bear River that feeds it on the Nevada/Placer County border suffer from high concentrations of mercury used by miners during the 49er era to extract gold from Sierra ore. Through the years, that toxic mercury has settled into the sediment and food chain to the point where the California Department of Fish and Game has ordered humans to not eat more than two fish per week out of Combie Reservoir and many other area bodies of water.

“We believe we can reverse that,” said NID Assistant Manager Tim Crough. “We want to restore the lake to its original capacity and remove all the mercury before it has a chance to contaminate the fish.”



Chevreaux Aggregates has been dredging sand and gravel in a pond next to the top of the reservoir for 30 years and releasing the sediment during the winter into the lake, Crough said. That has put more mercury into the reservoir and caused lake sediment to rise to the point that some boat owners are blocked from using their docks.

An initial test by Chevreaux showed high concentrations of mercury extracted from the pond sediment during the firm’s sand and gravel operations, Crough said. NID recently ran a larger test, dredging sediment out of the reservoir that was then placed in a Canadian machine designed to sift the mercury out, the results of which are pending.




“There’s nothing quite like this in the world,” said Ryan Jones, a representative for Knelson Concentrators of Canada, which rented the machine to NID. “We’re hoping that it will do the job sufficiently for the environmental people down there.”

“We want to find out if this is an effective means of extracting mercury without causing greater damage” by the dredging, Crough said. “It’s an experiment, and at the end, we may scrap it.”

A similar dredging experiment to remove mercury-laden sediment was done on the American River, Crough said, which only resulted in stirring up the mercury more and spreading it out. But that process did not include the Canadian mercury extraction machine.

Crough is hoping the results of the latest test can be used to attract state and federal grants to pay for the initial process. If successful, NID and a group of Sierra water companies and agencies it belongs to are hoping the process could be used in other area streams and lakes, as well.

An NID committee this week voted to spend $75,000 for environmental studies to be sent with the grant requests in conjunction with CABY, the group NID belongs to for the improvement of the Cosumnes, American, Bear and Yuba River watersheds.

The consortium is seeking a $2 million grant for a one-year project, with another $600,000 to be paid by NID, the United States Geological Survey and Chevreaux. The aggregate firm would get clean sand out of the deal to make concrete.

“I think it’s a tremendous idea,” said NID Director John Drew as he and fellow director Paul Williams voted to take the plan to the full NID board in the near future. “The potential benefit can’t be measured in dollars, and the environmental benefit will be huge; it’s for the greater good.”

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To contact Senior Staff Writer Dave Moller, e-mail davem@theunion.com or call 477-4237.


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