yankee doodle tailings pond dam

Pictured here is the dam that holds the Yankee Doodle Tailings Pond, seen from the bottom of the dam in 2015.

Citing a terrifying doomsday scenario, Atlantic Richfield Company wants the state to mandate an early warning system on Montana Resources’ Yankee Doodle Tailings Impoundment dam in the event of a catastrophic failure.

But Montana Resources, calling Atlantic Richfield's comments "inappropriate," says such an early warning system already exists.

In its comments to the state on an MR request to raise the dam, Atlantic Richfield lays out a frightening picture of a dam breach involving 30,000 acre-feet of mine waste inundating part of the town of Butte and spilling into the Berkeley Pit’s toxic lake, sending metal-laden, acidic water to a point of no return into the local groundwater. Horseshoe Bend Water Treatment Plant, which was originally built in 2003 to treat the pit’s water, would also be inundated and would be rendered useless.

Atlantic Richfield did not respond to a request for comment. The Department of Environmental Quality, which is reviewing Atlantic Richfield’s commentary as part of the permitting process for MR’s expansion request, said it would respond later in the summer to that and all the other public comments.

Mark Thompson, MR’s vice president for environmental affairs, said Atlantic Richfield’s comments are irrelevant because they are not based on current information. Thompson also said that in order for such a dam failure to happen, the events leading up to it would have to be “Biblical.”

The comments and others provided to the state by Atlantic Richfield Company last month suggest that the former oil giant is nervous about a potential dam failure. The company, now a subsidiary of global oil titan BP, proposed last month to build a brand-new water treatment plant near Shields Avenue to allow the pit to be drawn down possibly as much as 150 feet so the pit could “catch” mine waste if the dam – and all the 57 years of mine waste behind it - came crashing down.

Thompson said the dam, at its highest, is 750 feet and, at its base, is half a mile thick. At its crest, the dam is 300 feet wide.

Atlantic Richfield’s comment were precipitated by MR's request for a permit amendment with DEQ to raise the dam another 50 feet on its west side. Without that ability, MR’s 30-plus-year mining operation would have to close by 2021.

Dan Dennehy, Butte-Silver Bow County director of the Office of Emergency Management, said every major company, including NorthWestern Energy and REC Silicon, provides worst-case scenario studies. Such information helps both the companies as well as the county prepare for such events.

Dennehy also said the Yankee Doodle Tailings Impoundment dam is a “high-hazard” dam, as is Basin Creek Reservoir dam. The county has emergency response systems in place for both potential dam breaches, he said. Many Montanans live in river-bottom valleys and are within risk of a dam breach and subsequent catastrophic flood, he said.

Atlantic Richfield’s comments are not currently available for public view. The Montana Standard requested to see Atlantic Richfield’s comments this week, and DEQ complied.

Thompson said MR already has an early warning monitoring system in place.

“We have over 600 sensors in the dam transmitting data to us constantly in real time,” he said. “We (MR engineering staff) are automatically notified, and so is the control room, which is manned 24-7, if there’s something we need to watch and figure out.”

Thompson said the engineer of record, who is established by DEQ, is also automatically notified. Thompson said that, by law, the engineer of record has to contact DEQ if the dam's condition is cause for credible concerns of threat to human health and environment.

Atlantic Richfield cites a study MR created earlier this year which is not a part of MR’s permit application. According to Atlantic Richfield’s comments, the report describes a more severe impact if the dam should fail than appeared in MR’s permit application. The report found that “under certain conditions, inundation by materials from a hypothetical breach of the impoundment would extend beyond the mine’s boundary and into the city of Butte, including some residential areas.”

Atlantic Richfield recommends DEQ update and expand its emergency response plan in coordination with local officials to better protect residents who live within the inundation area.

Thompson said Atlantic Richfield is “misusing that study.”

Atlantic Richfield also wants MR to stop watering the “beach” of mine waste deposits that are near the dam area. Starting in 2013, MR began watering the “beach” with Silver Lake water, piped from 40 miles away, to keep the dust down.

But Thompson said that, too, is outdated information and that MR stopped using Silver Lake water for that purpose two years ago. He said now the mine keeps the dust down utilizing slurry water only. The slurry water comes from the mine waste.

He said MR also now implements multiple discharge points so the dam isn’t holding back excess water from wetting down the “beach” to keep the dust from flying around and bothering the nearby residents.

Dennehy said MR has been “very transparent” about emergency response scenarios and studies, and he said he feels “very comfortable” with MR’s plans. He said that in the event of such a catastrophe, the county would send out an alert through a first-alert network and also broadcast through radio and television to residents. The county emergency responders, along with MR officials, would set up an incident command and establish a strategy for a response.

Dennehy said that according to MR's projections, in order for the dam to fail, both of Moulton Reservoir’s dams, north of the tailings impoundment, would have to fail; there would be a 1-in-100-year snowpack; and it would have to rain 15 inches within 24 hours.

“We design to that so it would have to be something greater than that,” Thompson said. “There would have to be events that would exceed the edge of imagination for it to fail.”

Subscribe to Daily Headlines

* I understand and agree that registration on or use of this site constitutes agreement to its user agreement and privacy policy.

Nat'l Resources / General Reporter

Environmental and natural resources reporter for the Montana Standard.

Load comments