When sulfur in the soil is exposed to water, the runoff can damage streams and lakes. In extreme cases, acid mine drainage can kill everything in a body of water. Northshore owner Cliffs Natural Resources says it can stockpile the sulfur-laden rock to minimize contact with water. But environmental groups are calling on the state to conduct a more detailed study before allowing the expansion.
“This is 2014; we should know better,” said Paula Maccabee, attorney for Water Legacy. “Mining in high sulfur rock requires careful examination of scientific information, conservative assumptions, examination of alternatives to minimize harm, and caution in determining effects on both surface and groundwater.”
The Minnesota Department of Natural Resources has prepared a preliminary review, called an environmental assessment work sheet. Environmental groups are asking the DNR to conduct a more detailed environmental impact statement.
“Northshore Mining has worked with the Department of Natural Resources and Minnesota Pollution Control Agency over 10 years to develop the current mitigation plan for mining this area of the operation’s reserve,” Cliffs said in an e-mail. “If Northshore does not mine this area, it would reduce the life of the mine, thereby limiting the positive long-term employment and economic benefits of the operation for the surrounding communities.”
This is the first time the state has required any environmental review before allowing a taconite company to expose rock with sulfur content. Earlier exposures at the nearby Erie/LTV mine in the 1970s and 1990s resulted in acid mine drainage affecting the Dunka River, which flows into Birch Lake, a 7,000-acre lake popular with anglers for walleye and northerns.
LTV closed in 2000; Cliffs Natural Resources bought the property and is now responsible for cleanup. The company has spent years experimenting with constructed wetlands designed to purify the water, but sulfur and other pollutants running into the Dunka River continue to exceed limits in state statutes.
Now, in a 108-acre area on the edge of its 12-mile-long Peter Mitchell Mine pit just south of Babbitt, Cliffs plans to dig away millions of tons of surface material and bedrock each year to get at the taconite below. As mining progresses over seven to 10 years, workers will build a pile of waste rock. The sulfur-laden rock will be placed on top of 5 feet of crushed rock that doesn’t contain sulfur, to minimize contact with groundwater and stormwater, according to the state’s environmental work sheet.
The pile will be covered with a liner designed to minimize water infiltration, and topped with soil seeded with grass. Cliffs says it will cover the pile progressively before each section is likely to produce acid. The completed pile is expected to cover 153 acres. Water running off the pile will be directed to the Dunka River.
While Cliffs says the stockpile design will minimize acid runoff, environmentalists aren’t so sure. Kathryn Hoffman, an attorney with the Minnesota Center for Environmental Advocacy, said PolyMet, the proposed nearby copper-nickel mine, has gone into more depth studying how stockpiles could be designed. “They looked at placing liners under the stockpile as well as over it,” she said. “They developed strategies for collecting water from the stockpile. To me there’s not a good reason why the Northshore mine shouldn’t be looking at those strategies as well.”
Stephanie Hemphill, an environmental reporter who recently retired from MPR, is a freelance writer based in Duluth.