"Nothing in the [Brazil] dam failure changed what we've evaluated and the results of our stability analyses," Christie Kearney, PolyMet's environmental site director, said before the ruling. Both PolyMet and the Minnesota Department of Natural Resources said the dam was safe.
The U.S. Mine Safety and Health Administration, a Federal agency that enforces compliance in mining with health and safety standards, said it has met with Brazil's National Mining Agency to discuss Brumadinho. "Once the cause of the dam collapse is determined, MSHA will evaluate the findings and how they relate to practices in the United States," a spokeswoman said.
The Association of State Dam Safety Officials, a trade body that tries to improve U.S. dam safety, is considering recommending the addition of specific information about tailings facilities for the first time as it helps update the U.S. Federal Emergency Management Agency's guidance on dam safety regulation. It was last updated in 2007 and is tentatively planned to be updated in late 2020.
For now, though, tailings dams in most U.S. states are regulated in the same way as water dams, despite the fundamental differences in their materials, operations, construction and purpose, according to dam experts.
"There can be potential issues if the regulatory authority doesn't have sufficient expertise and experience with tailings dams," said Mark Ogden, a technical specialist at the Association of State Dam Safety Officials.
Environmental groups have used the powerful video of the collapse of the dam in Brumadinho, which was recorded by a camera on site, to capture the attention of the public.
In Queen Valley, Ariz., population 829, a March meeting to discuss a potential dam for a nearby mining project including a viewing of the video. About 300 people attended the event, sponsored by two local environmental groups, compared with about 100 who attended such meetings before the disaster, according to John Krieg, a retired electrician who lives in Queen Valley and attended the meeting.
"We'll be looking up at a 500-foot dam, containing 1.6 billion tons of toxic waste and wondering when it is going to collapse and bury the community," Mr. Krieg said.
A spokesman for Resolution Copper, a joint venture between BHP and Rio Tinto PLC that is proposing the mine, said the dam it plans won't have the upstream design of the one in Brazil. He said tailings experts, government agencies and the public are all involved in consultations for the project.
Environmentalists have for years opposed the plan for the new dam outside Embarrass. The project will build a new upstream mining-waste dam on top of an existing upstream dam -- which is already visible from Mr. Ehman's land. The project will almost double the dam's capacity to 525 million tons to hold waste PolyMet expects from a planned copper and nickel mine. Many people living close to the mine have embraced the plan, eager for the return of jobs to the region.
Mr. Ehman's property and 34 others sit inside what is called the "inundation zone" of the project: A full-blown failure would send a wave of waste reaching as high as 9 feet and traveling at speeds of up to 25 feet per second through the zone, according to a study by PolyMet.
No one told Mr. Ehman, a 61-year-old professional landscaper.
"Oh, jeez. What are you saying? That, possibly, could happen?" Mr. Ehman asked.
The inundation-zone report was published on the Minnesota Department of Natural Resources website but not flagged to Mr. Ehman and other residents interviewed in the zone, who didn't see it.
A spokesman for PolyMet said the company planned to inform residents in the inundation zone after they had concluded a second report on what would happen in the event of a collapse. The company said it has an evacuation plan in case of emergency, and that there are a series of lakes and water dams that would act as barriers to any serious spread of tailings in a breach.
The Minnesota Department of Natural Resources said the chances of a catastrophic breach are "very unlikely," based on the dam-break report that PolyMet completed. "No other project in the history of Minnesota had been more thoroughly evaluated," the department spokesman said.
Tony Licari, whose barn is visible from the north end of the existing dam, isn't worried. "We're a mining region," said Mr. Licari, who works as a pit supervisor at a nearby taconite mine. "It's what we do up here."
A Native American tribe that hunts and fishes close to the mine has expressed opposition, said Nancy Schuldt, water-protection coordinator with the Fond du Lac Band of the Lake Superior Chippewa. Brumadinho "played into the sense of dread we have about the likelihood of that sort of catastrophic failure," she said.
--Angela Calderon contributed to this article.
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