Looks like two interstate bridge piers at the mouth of the Blackfoot River won’t be coming out this year after all.
Even as the 53-year-old westbound bridge of Interstate 90 is replaced, the Montana Department of Transportation says it’ll wait to dismantle the piers until the effects on three upstream bridges are more closely studied and vetted.
The closest of those spans is the railroad bridge completed in 1908 by the Northern Pacific Railroad and now under Montana Rail Link supervision.
Both piers are detached from their bridge decks, and their removal was scheduled to start in July. Dwane Kailey, chief engineer at MDT in Helena, said new hydrological information regarding the impact on the bridges above prompted the delay.
“As a result of new information, MDT has postponed pier removal until we can determine the safest, most sustainable and cost-effective solution for this part of the project,” Kailey said in a recent message to resource agencies, including MRL and Missoula County.
“We intend to take the time to properly consider the new hydrological information available and determine the best course.”
Kailey could not be reached Monday to expand on what the new information was.
It’s the second year of what was expected to be a two-year, $15 million Bonner Bridges project. In 2018, Frontier West LLC of Missoula and the Helena-based engineering firm Morrison Maierle rebuilt the eastbound I-90 span.
The I-90 bridge piers were reinforced and enlarged by the U.S. Army Corps of Engineers as part of an Environmental Protective Agency’s Superfund project after the Milltown Dam was removed in 2008. That event drained a century-old reservoir that stretched up both the Blackfoot and Clark Fork rivers, increasing the rate of water flow as measured in cubic feet per second.
But concerns were soon raised over the larger piers and the safety of river users trying to get by them. In 2017, MDT announced a new plan to replace the half-century old bridges that would replace the in-channel piers with ones built on either side of the riverbank.
The closing of the gates of the new Clark (Milltown) Dam was delayed several days in early 1908 until the NP finished building the current piers and abutments of its Blackfoot River bridge. Nearly 100 years later, Russ Forba, EPA’s Milltown project manager, said the bridge was much more stable than other Blackfoot bridges, having been built on native alluvium.
“They’ve obviously done extensive maintenance in the 100-plus years since then,” MRL spokesman Ross Lane said. “That includes (Federal Railroad Administration) maintenance, which are twice-a-year inspections.”
Lane said the railroad has worked closely with MDT on various bridge projects through the years, “the biggest one being the Milltown Dam removal.”
“We don’t anticipate any impact to our structure or to our operations, but if impacts were to come up or if we do anticipate impacts, we’ll continue to work with them,” he said.
MDT will meet with the resource agencies in upcoming weeks, probably in early or mid-May.
“We intend to take the time to properly consider the new hydrological information available and determine the best course,” Kailey told the resource agencies.
“Any new work you do has to be run through the whole group of people” affected, said Sarah Knobel, public communications contractor for the state transportation department.
Knobel said it’s her understanding that pier removal won’t be undertaken this construction season “because there’d be such limited time to do the in-stream work.”
Kailey’s message said replacement of the bridge deck “will be ongoing according to schedule while we evaluate the new information.”
“As always, MDT prioritizes safety on this project. Our team will continue to focus on safety of the traveling public and work crews by notifying the public about river closures and interstate traffic conditions through robust outreaches,” he said.
Since mid-April the last mile of the Blackfoot has been closed to river users through the bridge construction area. It’s expected to remain so until late spring. With pier removal off the table in 2019, Knobel said river closures should be “very similar to last year.” There were two primary shutdowns in 2019, one before and the other after the busiest floating season.
“I can’t make any promises, but I do know last year the contractor worked very hard to make sure (the closures) were as limited as possible,” Knobel said.