Light rail plans corrected after "berm" flap

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April 22, 2014
By: Dylan Thomas
This Met Council map shows the two shallow tunnels planned for Kenilworth Corridor
Submitted image
Dylan Thomas
Metropolitan Council sent Minneapolis the wrong plans for Kenilworth Corridor tunnels, Chair Sue Haigh says

The Metropolitan Council published a “corrected and re-issued” version of its Southwest light rail plans April 22, several days after Minneapolis residents and officials raised concerns about the design of a tunnel.

To some, the more northerly of two shallow tunnels meant to carry trains through Minneapolis’ Kenilworth Corridor looked less like a tunnel than a berm. (Read that story here.) Met Council now maintains those designs were issued in error, but the original documents sent to Minneapolis and published online showed the north tunnel rising as much as 10–12 feet above current ground level.

In a statement released April 19, Minneapolis City Attorney Susan Segal said the north tunnel design was “inconsistent with previous representations made by the Metropolitan Council.” The tunnels were previously described by Met Council planners as “cut-and-cover,” meaning crews would first excavate a shallow trench and then cap it.

“Metropolitan Council staff have indicated that the new design is intended to keep the [light rail] enclosure above the water table,” Segal said, noting a berm had never previously been included in plans shown to the public or the city.

The base of both trenches will dip below the water table, and that has prompted concerns over potential groundwater impacts during and after construction. The design of the tunnels is intended to isolate them from groundwater and minimize leakage. A study conducted by a local engineering firm found no “fatal flaws” in the design.

Kate Brickman, communications director for Mayor Betsy Hodges, said city staff met with Met Council staff in the week following Met Council’s April 9 vote to approve the scope and budget of the Southwest light rail project. In those conversations, Met Council staff said the north tunnel berm was meant to keep it at least partially above the groundwater level in the area “and did not indicate it was a mistake,” Brickman said.

After questions were raised about the berm, Met Council first released a statement from Mark Fuhrmann, who leads light rail transit (LRT) development for the agency.

“The north shallow LRT tunnel design keeps the LRT tunnels in groundwater but not for the entire 2,500(-foot) length,” Fuhrmann wrote. “(Southwest) LRT project staff continue discussing the north tunnel elevation with Minneapolis staff.”

A statement from Met Council Chair Sue Haigh followed several hours later. According to Haigh, Met Council planners “made an error” and sent incorrect plans to Minneapolis.

Four days later, a new version of the planning document was sent to Minneapolis, and appeared to show a north tunnel design with the tunnel ceiling either at or below grade for most of its length.

It wasn’t immediately clear if the Met Council’s mistake would delay the timeline for municipal consent, the process of seeking official approval from Hennepin County the cities along the 15.8-mile light rail line. The deadline for municipal consent votes previously stood at June 29.