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Superfund mine site gets big work in '16

PIERRE -- A massive cap and fill project that could cost an estimated $89 million is planned this year for the Gilt Edge gold mine in Lawrence County, according to an official for the South Dakota Department of Environment and Natural Resources.

PIERRE - A massive cap and fill project that could cost an estimated $89 million is planned this year for the Gilt Edge gold mine in Lawrence County, according to an official for the South Dakota Department of Environment and Natural Resources.

Mike Cepak, a scientist in the state agency's mining and minerals program, said the work would concentrate on the western two-thirds of the abandoned site. The mine, located a few miles south of Lead, is one of two federal Superfund sites in South Dakota.

The property became the responsibility of state government after Brohm Mining Corp., walked away in 1999, unable to deal with the acid-rock drainage that plagues the site.

The U.S. Environmental Protection Agency, working with the U.S. Army Corps of Engineers and contractors, has been working on South Dakota's behalf to remediate and reclaim the site.

Brohm left behind 150 million gallons of acidic water in three pits. The amount keeps growing. A contractor for EPA treated 162 million gallons of water in 2015 alone. The year-end remainder was 39 million gallon, but the volume now is back to 50 million.

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The acid results from sulfidic ore making contact with oxygen and water. The sulfidic rock needs to be kept from exposure to air and moisture. Artificial and natural materials serve as protective caps. Water monitoring and treatment will be a long-time need.

At this point EPA pays either 90 percent or 100 percent of costs at the site. State government's share is either 10 percent or zero, depending on the work.

When EPA removes the site from the Superfund list, state government would become responsible for 100 percent.

South Dakota has $17,774,000 in a special account for that purpose. Cepak told the state Board of Minerals and Environment at its meeting Thursday: "It's slowly growing."

The work set to start this year and continue into 2017 calls for building new storage and removing to it water and sludge from several old mining pits such as Sunday and Dakota Maid. Those pits then would be backfilled.

To reduce operating expenses for water treatment and monitoring, a remote sensing system was installed at a cost of about $909,000, according to Cepak. He said the technology should save $700,000 annually.

He told the board the hope is to get as much done as possible while EPA is still at the site. "So our maintenance costs are minimized as much as possible," he said.

South Dakota's other Superfund site is at Ellsworth Air Force Base east of Rapid City.

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