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Vast deposits of prime silica sand lie beneath the surface of Washington County, but whether they’re rich enough to attract mining companies seeking fortunes from the oil industry’s fracking boom might be a matter of economics.

The coarsest silica sand, most valuable to mining companies, would be found on the bluffs along the St. Croix River and protected by a complex “regulatory framework,” said Tony Runkel of the Minnesota Geological Survey.

“I’d be surprised if a company made a strong effort to have any sort of major operation in Washington County,” he said. “I don’t think that geologically it’s attractive enough that they’d want to step through more hurdles than they would someplace else.”

A community forum Tuesday night in Mahtomedi — “Frac Sand Mining: Could it Happen Here?” — will examine just that point. Oil booms in North Dakota and elsewhere use hydraulic fracturing, known as “fracking,” to extract oil from bedrock. Silica sand operations have inflamed public opposition in Winona, Minn., and Maiden Rock, Wis., among other places. Opponents cite noise, nonstop truck traffic, lung damage from inhaling dust, and water pollution. Supporters counter that silica sand mines bring jobs and help ensure U.S. energy independence.

“I know it’s a big concern with folks on both sides of the issue,” said Gary Kriesel, a county commissioner whose district includes a stretch of St. Croix riverfront from Stillwater to Afton. “We’re going to have to get educated on this real fast. If they even put a shovel in the ground for silica mining in Washington County it’s going to attract a lot of attention.”

Washington County’s only silica mine, in northeast Woodbury, has operated since 1972. The city recently renewed an interim conditional use permit for another year for the operator, Preferred Sands, on land owned by Black Diamond Granules Inc. Senior planner Eric Searles said Preferred Sands is actively extracting silica sand and has responded well to concerns over spills on roads and noise complaints. The owner of a family RV park across the road said he called a Preferred Sands manager in the middle of the night when a bearing was squealing at the plant and the noise stopped within 15 minutes.

“They’ve been an excellent neighbor,” said Rick Poss, whose family hosts 60-70 RVs on a summer night. “Totally responsive. I couldn’t say enough positive things about them.”

No new proposals for large-scale silica sand mining have surfaced in Washington County, in part because larger deposits of silica sand are available farther south along the Mississippi River. Runkel said oil companies prefer coarser quartz sand because it’s more effective in fracking, but it’s possible that miners could make money with lesser grades of sand if fracking demands increase.

Washington County has chunks of land where that lower-grade sand could be easy to extract, he said.

“I’m not even aware of any prospecting,” said Heather Arendt, industrial minerals supervisor at the Minnesota Department of Natural Resources. Any company proposing to open a silica mine — often much larger and busier than traditional mines — would face a “quiltwork” of government permits and environmental reviews, she said.

Such scrutiny was evident recently in Scandia, where Tiller Corp. tried for years to reopen a dormant sand and gravel mine. After several public hearings where opponents objected to noise, heavy big trucks, and the mine’s proximity to the federally protected St. Croix River, the City Council voted to reopen the mine. The city’s permit, however, specifies that Tiller can’t mine for silica sand — a prohibition that opponents had wanted.

Becky Siekmeier, a member of Mahtomedi Area Green Initiative, said the Tuesday forum is being held to raise public awareness that frac sand mining isn’t a short-term issue, or one confined to current controversies.

“With the fracking boom in North Dakota expected to last 30 years it’s possible it could happen right here,” she said.

Kevin Giles • 651-925-5037