Downtown Minneapolis is about to get a bit noisier and dustier, maybe even vibrate a little. Along 4th Street, bus and bike lanes will disappear and traffic lanes will be reconfigured.

It's all part of a big project that kicks off Monday when the Metropolitan Council's Environmental Services division begins repairs on an aging sewer pipe buried 80 feet below the street inside a sandstone tunnel that's starting to wear away.

The good news, project manager Jeff Schwarz said, is that the 15-month project should not bring major disruptions for motorists and pedestrians.

"That is what we are hoping for," he said. "Sidewalks will remain open and there should not be any traffic volume issues."

All three eastbound lanes between 2nd Avenue N. and 4th Avenue S. will remain in place (there may be some brief lane closures at the outset), but they will shift to the north side of the street. To do that, the bicycle lane and the westbound lane used by Metro Transit buses will be eliminated.

Northbound and westbound bus Routes 3 and 7, which now use the bus-only lane, will shift to 3rd Street while northbound Route 14 buses will move to 7th Street. Eastbound and southbound buses will remain on 4th Street, said Metro Transit spokesman Drew Kerr.

Bicyclists, on the other hand, will lose the lane they've had to themselves since it went in during the early 2000s.

The sewer pipe was put in during the mid-1880s, and it's still in decent shape, although it has a few cracks, Schwarz said.

The tunnel, however, is showing its age. Builders left a small void between the pipe and the top of the tunnel, and after more than 130 years, the tunnel's top is deteriorating, he said. Small pieces of sandstone periodically come loose and have the potential to fall and damage the line.

Dump trucks and cranes will roll in Monday to start repairing the pipe and stabilize a quarter-mile of the tunnel wall. Crews will drill two access shafts on the south side of 4th Street (the side adjacent to City Hall). One will be near Hennepin Avenue and the other near Marquette Avenue.

The process, complicated by the depth and tight quarters, will include removing as much as 2,000 tons of debris, repairing any damage and filling the void with grout.

All that work comes with a warning: "Typical impacts related to this type of construction include traffic and pedestrian disruptions, periodic early morning and late night work hours, lights, dust, noise and vibrations," an advisory on the Met Council's project description reads.

The Met Council timed its work to wrap up just as the city of Minneapolis plans to begin transforming 4th Street, said Met Council spokeswoman Bonnie Kollodge.

Later this year, the city will start moving utilities under 4th Street ahead of a planned 2020 project to rebuild 4th between 2nd Avenue N. and 4th Avenue S.

In the new arrangement, 4th Street will have three eastbound traffic lanes 10 to 11 feet wide from 2nd Avenue N. to 3rd Avenue S. That will drop to two lanes between 3rd and 4th avenues S. On that block, instead of a third traffic lane, there will space for short-term parking and deliveries at City Hall.

Sidewalks on both sides of 4th Street will be widened to about 20 feet, plus extra bump-outs at street corners. Signals compliant with the Americans with Disabilities Act, better lighting and a protected bike lane are also planned.

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