Dam’s toxic silt poses challenge

MILLTOWN, Mont. – Dismantling the dam built a century ago at the confluence of two rivers in Western Montana will be the easy part. It’s dealing with the contaminated mud behind the dam – enough to fill a freight train more than 500 miles long – that poses the big challenge.

The Environmental Protection Agency expects Milltown Dam, at the terminus of the nation’s largest Superfund environmental cleanup site, to be taken down in the winter of 2006-07.

There’s experience to draw on in removing the aging dam – Wisconsin alone has eliminated more than 100 – but Milltown stands out for having all that mud contaminated with heavy metals, mining contamination that washed 120 miles down the Clark Fork River.

That some of the sediment will be removed is a triumph for environmental groups and others who campaigned for years to take it out. Skeptics, however, say disturbing the mud could introduce new problems.

By everyone’s account, it is a huge undertaking.

“The combination of the dam removal and sediment removal and restoration is something that I’m not aware of happening anywhere else,” said Peter Nielsen, a public health official in Missoula, a few miles downstream of the dam, and was an early activist on Clark Fork water pollution.

With the support of then-Gov. Judy Martz, the EPA last year decided that the dam at the confluence of the Clark Fork and Blackfoot rivers should come down, and that about one-third of the 6.6 million cubic yards of sediment laced with arsenic and other contaminants should be dredged for disposal 100 miles away. The contaminants leached from old mines upstream in the Butte area.

While some preliminary technical work is already under way, most of the action these days is behind closed doors as the major players negotiate an agreement spelling out who’s responsible for what. EPA project manager Russ Forba said he hopes that agreement, which requires court approval, is completed in June.

Financial responsibility for the $100 million in work rests largely with Atlantic Richfield Co., which acquired assets and liabilities of the Anaconda Co. mining company. Money also will come from the dam’s owner, Northwestern Corp.

Forba said that if the dam is removed in 2006-07, then the sediment likely would be taken out in 2007-08 and restoration of the area would begin in 2009.

“That’s if Mother Nature cooperates and things go as planned,” he said. “It’s an active system, so you can’t always predict.”

Water and power companies, along with the state Transportation Department, say the timetable isn’t the only uncertainty.

Mountain Water Co., which supplies 60,000 residents of Missoula, worries the Milltown project will raise the arsenic level in the Missoula aquifer. PPL Corp. envisions contaminated sediment that is not removed eventually washing about 150 miles downstream, to the company’s dam at Thompson Falls. The Transportation Department says taking out the dam could harm roads and bridges nearby.

“We think the long-term answer is probably removal of the dam and the sediments,” said Arvid Hiller, Mountain Water’s general manager. But potential effects have not been researched adequately, he added.

Nielsen, water quality supervisor for the Missoula City-County Health Department, said the aquifer issue has been investigated and the findings do not support Hiller’s concern. As for PPL’s dam, Nielsen said the Clark Fork is much bigger downstream than at Milltown, and the amount of sediment carried to Thompson Falls would be insignificant relative to the water volume there.