Envirocon, the company hired to remove the dam, released its first preliminary design report last week, outlining the proposed 10-foot lowering of the reservoir level.
The preliminary design report is the first of what will be many technical reports over the next few years describing different aspects of the project. Each report will go through three revisions - a draft, a draft final and the final version.
“The good news is that all the reports will be done using a similar format,” he said. “People should get more comfortable with them as time goes on.”
The first report considers potential impacts of the 10-foot drawdown needed to dry out sediments that will be removed during construction of a temporary bypass channel for the Clark Fork River. The hope is the drawdown can begin sometime in June - so high water during the annual spring runoff can dilute any sediment that might be scoured from the riverbed or banks.
It's advantageous to all concerned to get the work started this spring, Fein said.
“For us, it gets the reservoir down well ahead of the time we'll begin working to build the bypass channel,” he said. “That gives those sediments more time to dry and our work becomes more straightforward and with less risk.”
“If the drawdown occurs during high water, it also dilutes whatever material might be scoured from the banks. There will be less impact to the environment than if we were to try the same thing during low flows,” Fein said.
The next stages, which include diverting the river into a bypass channel and beginning the dam's removal, will be much more involved, Fein said.
“Everything we do with this first drawdown is reversible,” he said. “Everything can be undone. That won't be the case later on.”
Drawdowns of Milltown Reservoir aren't new, said Peter Nielsen, environmental health supervisor at the Missoula City-County Health Department. Similar lowerings have occurred in 2002, 2004 and last fall.
“It's not like we haven't done this before and have no idea of what might happen,” Nielsen said. “We actually expect to see a little less impact from scoured sediment during this drawdown. It's just no longer there.”
Last fall's drawdown for the removal of the Bonner Dam was the “cleanest one we've ever seen,” he said.
District Judge Sam Haddon of Great Falls recently signed the long-awaited consent decree, the document that outlines who will do what and how much they'll pay for the federally supervised Superfund cleanup.
“Assuming everything goes through, the consent decree will become effective on April 10,” said Nielsen.
Now, with the release of Envirocon's first preliminary design report, Nielsen said the process “is moving forward. There still are a lot of details to work out, but now it's out in the open and it can proceed.”
The report considers a list of potential impacts of the drawdown, including surface and groundwater issues, bridges and dam safety. Fein said the next draft will include additional information on contingency planning.
“We still have to get approval from EPA and the state,” Fein said. “It does look good. We haven't found any fatal flaws.”
The time frame is short if Envirocon wants to get started by June.
“In order for us to get Stage One started, it's going to require a lot of hard work by the agencies to get this turned around and quickly,” Fein said.
Reporter Perry Backus can be reached at 523-5259 or at pbackus@missoulian.com
See for yourself
Want to take a look at the document? Go to the Clark Fork River Technical Assistance Committee's Web site at http://www.cfrtac.org
There is a link to the report under the headline “Milltown Preliminary Design Report looks at first drawdown.”
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