LINCOLN – Beth Ihle envisions a Butte pasty when she explains how a huge pit in the hills east of town will hold 800,000 cubic yards of Mike Horse mine waste.
“You know how when it’s cooked just right, the potatoes are all tender and the meat holds together and doesn’t crumble when you bite into it?” the U.S. Forest Service geologist said as she walked up the berm above Montana Highway 279. “That’s what we want here.”
The pasty is a hardrock miner’s meat-and-potatoes lunch staple wrapped in pastry. In this case, a layer of natural clay topped with plastic sheeting and drain gravel forms the crust around a toxic filling big enough to cover three football fields 40 feet deep.
The top will be covered with the same layer, followed by topsoil and native plants, so any rain or snow landing there should never reach the acidic heavy metals inside.
That’s essential, as the repository sits barely 200 yards from the headwaters of the Blackfoot River. Despite that nearness, Montana Department of Environmental Quality construction manager Shellie Haaland said the location was far safer than any of 13 other considered sites.
“If we have a catastrophic event big enough to release anything from that repository, we won’t be worried about that,” Haaland said. “We’ll be worried about everything else.”
Tests on the pit’s protective layer showed a 6-inch version would keep the most toxic materials from seeping out for 3,000 years. In construction, that layer will be 2 feet thick.
The tailings come from the Mike Horse mine, which lies about three miles due east of the pit. The mine produced a little gold and silver and a lot of lead and zinc before and after World War II.
In 1975, a catastrophic flood blew out an earthen dam below the mine, washing hundreds of thousands of cubic yards of mine waste down the creek drainage and into the Blackfoot River. That event poisoned the river fishery for decades, and some tributary creeks remain sterile today.
The tangle of creek canyons below the Mike Horse are geologically complex, full of hillside springs and very steep. Ihle and Haaland said that combination of factors killed hopes of capping the waste in the canyons where it was piled, or stuffing it back into the mine tunnels it came from.
During the wet spring of 2011, DEQ spent almost $350,000 on pumps and emergency drainage to keep the old dam from failing again.
Engineers considered building a road over the ridge between the mine and the repository to avoid public traffic. But the geological challenges and steepness made the new road too expensive and unsafe. That left removal to be trucked down the Mike Horse road, onto Montana Highway 200, over to Highway 279 and to the site – a journey of 6.5 miles.
On Thursday, DEQ will open bids for that trucking job. That’s been one of the most contentious parts of the project for Lincoln residents, who weren’t happy about three or four summers of all-day dump-truck traffic. Because of weather conditions at more than 5,000 feet above sea level along the Rocky Mountain Front, the construction season lasts barely 100 days a year.
The project was contentious enough that several residents sued the state in 2012, claiming it was illegal to lift some protective covenants that protected the area for ranching, timber and residential use. Haaland and Ihle said while that lawsuit is still pending, it has not blocked the state and federal governments from going ahead with construction of the repository.
“We don’t deny their world will have a construction backdrop for a while,” Ihle said. “We’re working so we can go faster and they can get on with their lives.”
A 2006 bankruptcy court settlement with mine owner ASARCO provided $39 million for the project. The Forest Service contributed another $1 million for planning and administrative costs. The state got the 360-acre parcel along Highway 279 from Stimson Lumber Co. as partial settlement of costs related to cleaning up toxic waste at its lumber mill in Milltown, east of Missoula.
The first third of the repository pit should be ready by summer, when dump trucks will begin moving loads out of Mike Horse. If the weather and engineering cooperate, the project could be done by 2017.