Shallow LRT tunnel no danger to lakes, engineering firm says

Report finds no “serious concerns,” but says more detail is needed

In concept, a shallow tunnel for light rail trains through Minneapolis’ Kenilworth Corridor raises no “serious concerns” for the Chain of Lakes, according to an engineering firm’s report.

The letter from Maple Plain-based Wenck Associates, Inc., is one more piece of information for the Metropolitan Council to weigh as it prepares for a key decision on the Southwest Light Rail Transit project next month. It’s scheduled to pick one of two options on Oct. 9: shifting freight trains to St. Louis Park to make room for light rail or keeping them in the narrow Kenilworth Corridor by running light rail trains below ground.

The shallow tunnel is still in the concept stage, and Wenck noted that its findings could be amended as more information becomes available. At this point, though, the firm does not expect the tunnel to impact water levels in three nearby lakes: Lake Calhoun, Lake of the Isles and Cedar Lake.

If built, the tunnel would require a drainage system. Engineers anticipate having to drain away groundwater that seeps through tunnel walls, as well as any rain that enters the tunnel during storms.

Water removed from the tunnel would filter through an infiltration system before returning to the environment. That system should be able to handle a once-in-50 years storm without spilling potentially contaminated water into the lakes, the report indicates.

That didn’t totally satisfy Mayor R.T. Rybak’s policy director, Peter Wagenius, who represents the mayor on the project’s Corridor Management Committee. When the committee reviewed the report Wednesday morning, Wagenius noted global climate change had led to an increased frequency in major storms and flooding.

When it comes to the Chain of Lakes, he added, the “stakes … are extraordinarily high.”

Minnehaha Creek Watershed District hired Wenck to prepare the report, and in a separate letter the agency noted the tunnel concept was “not adequately detailed” for it to issue a permit at this point.

The local officials who make up the project’s Community Management Committee reviewed both letters Wednesday morning. A week prior, a non-binding decision by that advisory body basically eliminated a third option, a deep-bore tunnel for light rail trains, citing its $330-million price tag.

By comparison, the freight rail-rerouting plan is projected to cost $190 million–200 million. Estimates for the shallow tunnel come in at $150 million–$160 million.

The Metropolitan Council should have more information on the cost and viability of rerouting freight rail within the next few weeks.

Jim Alexander, the project’s chief engineer, said the agency had plans to meet later this month with representatives of Transportation Technology Center Inc., a railway testing and research firm based in Pueblo, Colo. TTCI will run simulations on several rerouting options, including some previously rejected by railroad officials, Alexander said.