Builders of the $2.7 billion Southwest light-rail line have determined that an underground concrete slab discovered while constructing a tunnel for the line in Minneapolis isn't part of the structural underpinnings of a nearby condominium building.

The impediment, which was detected last month, is a triangular 20-square-foot piece of unused concrete associated with the condos, which were built in the early 1900s as grain silos. The silos were repurposed as residential units, now known as the Cedar Isles Condominiums, in the 1980s.

Crews on Thursday sawed through and removed the slab, which is about 18 inches thick, said Trevor Roy, spokesman for the Southwest project. He said it was unclear how much removal of the slab will cost.

A tunnel for light-rail trains is being constructed within feet of the condos, using a 500-foot secant wall to provide excavation support. Construction of the wall is expected to resume in coming weeks.

The 14.5-mile Southwest line, which will connect downtown Minneapolis to Eden Prairie, snakes through the narrow Kenilworth Corridor in Minneapolis between Lake of the Isles and Cedar Lake.

Vanne Owens Hayes, president of the Cedar Isles condo association, said Thursday that she was relieved the slab was deemed nonstructural and removed. She said she'll be "more relieved" when the entire project is done.

Cracks have surfaced in ceilings and floors of the condo building, and its underground parking garage flooded last year after a water main break during light-rail construction. That's in addition to noise and the inconvenience associated with a large construction project.

Condo owners and the Metropolitan Council, which is building the Southwest line, currently are engaged in a mediation process led by Kathleen Blatz, former chief justice of the Minnesota Supreme Court. There are 109 condos in the former grain silo structure.

Southwest, the most expensive public works project in state history, is more than 70% complete. It is more than $1 billion over budget and its opening has been delayed for nearly a decade, partly because of the difficulties associated with building the half-mile-long tunnel.