Modern gold-mining technology may be tapped to undo environmental damage caused by Gold Rush-era mining practices that left many Northern California waters tainted with mercury.

The Nevada Irrigation District proposes a pilot project to remove mercury from Lake Combie, a small reservoir on the Bear River that straddles the Placer-Nevada county line between Meadow Vista and Lake of the Pines.

The project will be watched with interest throughout the mercury-laced Gold Country – by water and mining officials as well as by residents who live nearby.

Tim Crough, the district's assistant general manager, said the Combie project would combine dredging with a centrifuge process to "spin" the mercury out of water extracted from the lake.

"It's a pretty novel approach," said Charles Alpers, a research chemist with the U.S. Geological Survey in Sacramento and a consultant for the project.

The work, which could begin in 2010, would remove accumulated sand and gravel that can make boating difficult. But the primary goal, Crough said, is to improve water quality.

The district is seeking grants for the project, which is expected to cost $6 million to $8 million, he said.

During the California Gold Rush, miners used about 6,600 tons of mercury to recover about half that much gold. Heavier particles sank in sluices, but finer mercury particles washed out and became embedded in sediment in streams and lakes.

Until recent years, the mercury deposits were of little concern.

"The thought was that mercury was trapped behind reservoirs, and if you didn't stir it up, it was OK," Crough said. "But it gets stirred up with every storm, and it goes over the dam."

Mercury, which is harmless in its elemental form, is not considered a drinking water hazard, Crough said. But transformed into methylmercury, it is taken up by plants and fish and becomes more toxic as it moves up the food chain.

Methylmercury impairs the nervous system. Women and children are particularly at risk.

The California Environmental Protection Agency in 2003 issued a health advisory after high concentrations of mercury were found in watersheds of the Bear and Yuba rivers, major sites of hydraulic mining. The agency urged limiting consumption of fish from certain Sierra lakes and streams, including Lake Combie.

Rick Humphreys, an engineering geologist with the state Water Resources Control Board, found that suction dredging – a common method of mining sediment from the bottom of a stream or lakebed – is not very effective in removing mercury.

"But nobody's come up with a better mousetrap," he said.

Humphreys said he intends to look closely at the pilot project, which would run the return water through a giant centrifuge, developed for gold mining by Knelson Concentrators of British Columbia, to remove those fine mercury particles.

Chevreaux Aggregates had mined the Lake Combie area for more than 30 years before the 2003 state EPA advisory, Crough said. But the mercury problem must be solved before aggregate mining can resume there.

The presence of the nearby gravel plant, with its sediment basin, makes Lake Combie the ideal test site, Crough said.

But some Meadow Vista residents are wary.

Jeff Evans, a member of the Meadow Vista Municipal Advisory Council, said many residents think the effort has more to do with fostering mining operations than removing mercury.

Louis Sigmond, council chairman, said, "It seems like a very noble experiment … but I'm not sure if it's good for Meadow Vista."

Sigmond said concerns center on truck traffic and air pollution. Unless those issues are resolved, he said, the project faces community opposition.

Call The Bee's Cathy Locke, (916) 608-7451.