Milltown Dam comes down

By John Cramer - 03/29/2008

MILLTOWN — Milltown Dam, a 100-year-old landmark that came to symbolize the economic prosperity and environmental destruction of Montana’s mining industry, came down Friday.

The forces of man and nature combined in the form of tons of water seeking the path of least resistance and a heavy equipment operator who dug out the last of a temporary earthen dike to allow the Clark Fork and Blackfoot rivers to flow freely for the first time in a century.

Beneath sunny skies and snow-covered mountains, hundreds of people gathered to watch from the riverbanks and a bluff above Milltown Reservoir, which marks one end of the largest Superfund site in the nation.

“I feel like an 8-year-old kid waiting for Christmas,” said Chris Brick, staff scientist for the nonprofit Clark Fork Coalition.

Before the breaching, Sen. Max Baucus, Sen. Jon Tester and other officials told the crowd that the Milltown project represented Montana’s shift from an extraction to a restoration economy, creating jobs that protect the environment and use the state’s natural resources in sustainable ways rather than plundering them.

“We all know Montana is perfect, and today we are making it more perfect,” Baucus said.

At noon, Gov. Brian Schweitzer shouted: “Let ’er run!” And the rivers starting as a trickle that became a torrent that became a muddy waterfall poured through the channel where the dam’s old powerhouse and north abutment were demolished in January.

Removal of the other half of the dam made up of the spillway, radial gate and divider block is slated to start this summer and be complete next spring as part of the $120 million cleanup, restoration and redevelopment of the reservoir area paid for by the Atlantic Richfield Co., which bought the old Anaconda copper company.

Rather than a “blow-and-go” dam detonation that releases a river suddenly, the Milltown breaching was designed to let the water pressure slowly erode the earthen dike.

Working right up to breaching time, heavy equipment operators had scooped away most of the dike, dug a pilot channel, removed dewatering wells to allow underground seepage and partially closed the radial gate measures meant to encourage the rivers to take their natural course.

At the governor’s signal, the proverbial plug was pulled and the rivers, whose confluence is just above the dam, did the rest.

The initial 15-foot-wide gap widened under the water pressure, which slowly head-cut its way up through the breach and created a crumbling chasm.

Throughout the day and into the night, the dike’s disintegration accelerated like a sand castle being washed away by a rising tide, sending timber beams, stumps, rocks and other debris downstream.

The river’s thalweg or the strongest current in the deepest part of the river was expected to push through the channel and obliterate the remaining dike late Friday or early Saturday.

Federal, state and local officials, river advocates, construction workers and others cheered as the dam came down.

BREAK “This is a significant achievement that everyone can be proud of,” said Matt Fein, Milltown project director for Envirocon, the Missoula-based contractor for the cleanup and dam removal.

“This is an incredibly important milestone,” said Karen Knudsen, executive director of the Clark Fork Coalition, which campaigned for two decades to have the river cleaned up and the dam and contaminated sediment removed.

“This is what we’ve been working toward,” said Peter Nielsen, environmental health supervisor in Missoula’s City-County Health Department.

The breaching dropped the reservoir’s water level another 14 feet and raised the downstream water level for several hours afterward, although the river rose less than expected because cool spring temperatures have slowed snowmelt.

The river’s rise moved imperceptibly downstream, where people gathered along the riverbanks to watch, including a crowd gathered on the Higgins Avenue bridge. One man joked: “I’m waiting for a tsunami.” At the dam site, the water initially plunged 20 feet through the breach the elevation difference above and below the dam but that grade will flatten out as the rivers return to their natural levels.

Larger dams than Milltown have been removed, but few have been as complicated because of the copper, arsenic and other heavy metals contaminating sediments behind the dam.

The project is expected to have profound changes on the Clark Fork’s physical, biological and chemical makeup as it readjusts to its natural state.

The breaching will release an estimated 300,000 cubic yards of uncontaminated sediment scoured from the mouth of the Blackfoot River over the next several months.

Another 3 million cubic yards of clean sediment is projected to move downstream along the Clark Fork over the next decade, the largest sediment load ever released by a dam removal in the United States.

A large number of fish, insects and other aquatic organisms will die in the short term, but the rivers’ release will allow bull trout, a threatened species, and other fish to spawn upstream and the ecosystem is expected to start recovering in several years.

The breaching was a symbolic milestone, culminating more than two decades of policy discussion, scientific research and public debate, but years of work remain on the site’s cleanup, restoration and redevelopment.

BREAK Since the 1860s, metal mining and smelting in and around Butte’s “Richest Hill on Earth” generated riches for William Clark and other “copper kings,” and jobs for legions of lunch-pail workers, but the industry also poisoned a huge swath of water, land and air in southwestern Montana.

The Milltown Dam, a hydroelectric facility made of timber, stone, concrete and brick, was completed in January 1908 at the confluence of the Clark Fork and Blackfoot. A flood six months later washed tons of toxic mine tailings downstream, poisoning the riverbottom, streambanks and floodplains before settling behind the dam.

The Clark Fork, which periodically ran red with mine wastes, carried copper that killed fish, arsenic that tainted Milltown’s drinking water and other metals that sterilized streambanks.

In 1983, the U.S. Environmental Protection Agency designated 120 miles of the Upper Clark Fork Basin as a Superfund site.

The EPA is removing the dam and the worst of the reservoir’s sediments 2.2 million cubic yards, while another 4 million cubic yards will be stabilized and left in place in an effort to clean up the drinking water and environment. Stimson Lumber Co.’s diversion dam on the Blackfoot also was removed as part of the project.

The Clark Fork cleanup started in 2006 and is scheduled for completion in 2010.

The EPA is paying for new drinking water wells for residents, while the aquifer is projected to clean itself out over the next four to 10 years.

Work also is under way to restore the confluence’s natural floodplain and redevelop the site as a public park, a process scheduled to take another five years or more.

Milltown Dam stopped the rivers from doing what the laws of physics, hydrology and nature compelled them to do run downhill on a path to the ocean.

Preparing for the breaching, project officials spent years calculating volumetric flow rates, fluid dynamics, deterministic hydrologic modeling and other scientific and engineering factors all designed to predict what the rivers would do when released, to prevent the mine wastes from being scoured and to minimize damage to the environment as the rivers are brought back to their natural state.

“It’s gone even better than expected,” said Russ Forba, the EPA’s Milltown project manager.

All week, construction workers prepared for the dam’s breaching, laboring under a mix of sunshine, spring snowstorms and a cold wind blowing through Hellgate Canyon.

A mile upstream from the dam, workers finished installing a temporary dike to divert the Clark Fork into the project’s bypass channel to reduce erosion and prevent the mining wastes from being scoured downstream.

At the dam, bulldozers, excavators, dump trucks, giant jackhammers and other heavy equipment restored the landscape to its historic grade.

For the next year, the rivers will flow through the powerhouse gap until a permanent channel is created where the spillway is located.