CLEVELAND, Ohio -- The Cargill salt mine below Lake Erie has stopped mining because of concerns that the roof 1,800 feet below ground could collapse.
That's according to Cargill spokesman Mark Klein, who said the company stopped mining salt on Monday after its first shift, sending about 100 employees home for the week with pay.
"We don't want anybody in that area in case part of the roof comes down," Klein said.
The problem is called "convergence," Klein said. "Either the floor is coming up a little or the ceiling is coming down a little."
Klein said Cargill monitors measurements of the shaft and the room at the bottom of the mine on a regular basis.
"We're looking for movements of like one one-hundredths of an inch," he said.
The mine has been operating for more than 50 years and has been owned by Cargill since 1997. The salt is extracted from the face of the mine using ammonium nitrate explosives.
The company is still operating and shipping salt, it's just not mining any new salt, Klein said. About 75 people are still working above ground at the site.
"Over the past few weeks we've seen some data points that we need to do more study on," Klein said.
Asked if the company has had previous safety concerns with the mine, Klein said, "Nothing quite like this."
Cargill notified the Ohio Department of Natural Resources about the closure this morning "and they said they didn't need our assistance at this time," ODNR spokesman Mark Bruce said.
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ODNR inspectors will stay in contact with Cargill and its experts, he said, while Cargill will determine "what action they are going to take to remedy the situation."
An ODNR inspector will monitor progress and the mine will not reopen until ODNR gives its approval, Bruce said.
Bruce did not express any concerns about adverse effects on Lake Erie.
A typical coal mine is 100 to 200 feet below ground, he said, while the Cargill salt mine is 1,700 feet below the bottom of the lake, which means it's highly unlikely a breach of the mine would contaminate the lake.
The Cargill mine is a major supplier of salt to states and municipalities across the snow belt, many of which probably have leftover salt from milder winters the past two years, Klein said.
Last year, Cargill supplied road salt to 48 Ohio counties, more than any other salt provider in the state, according to a spokesman with the Ohio Department of Transportation, but this year it's slated to supply only 33 counties.
Should the Cargill mine be closed permanently, the market would adjust and production would increase elsewhere, Klein said.
"We have two other mines in the U.S.," Klein said. "We also have competitors."
Klein said Cargill has salt mines in southern Louisiana and under Cayuga Lake in Lansing, N.Y.
Klein said many of the customers served by the Cargill mine have their prices for road salt this winter locked in under contract.
Ohio Attorney General Mike DeWine filed an antitrust lawsuit in 2012 against Cargill and Morton Salt, which has a mine at Fairport Harbor, claiming they conspired to keep road salt prices artificially high.
A Tuscarawas County judge dismissed one of the counts, which claimed monopolization, in April, while another count claiming conspiracy still is proceeding, said Dan Tierney, spokesman with the Ohio Attorney General's Office.
In 2010, Cargill Deicing Technology announced it was spending $13.8 million to expand the capacity of the mine operations based on Whiskey Island at the mouth of the Cuyahoga River.
"It's all done," Klein said of the expansion. "A lot of it was for additional conveyor belts."
Companies operating at the Cargill mine site were cited with violations or orders by the U.S. Department of Labor's Mine Safety and Health Administration 14 times in the past month, but none of the concerns appear to involve the structural integrity of the mine.
Cargill Deicing Technology was issued six of those citations for violations, including two considered significant and substantial, according to the Mine Safety and Health Administration website. One of those had to do with keeping the workplace neat and clean and the other with ensuring safe passage on the site.
A spokesman for the Mine Safety and Health Administration said inspectors and technical support personnel are on site and investigating.
Mine workers are represented by Teamsters Local 436. Its president, Gary Tiboni, could not immediately be reached for comment.