– The $343 million highway interchange project scheduled to start this spring with traffic headaches on I-35 has been pushed back a year.

Already scaled back due to a $100 million funding gap that arose while planning the project, the Minnesota Department of Transportation said Wednesday that "after more in-depth analysis" major work on the Twin Ports Interchange aka "Can of Worms" won't start until spring 2021.

Issues with contaminated water and soil at the project site have piled up to the point that the department said more time is needed to re-evaluate how to deal with it all.

"This is an old area of industry," said Pat Huston, MnDOT's assistant district engineer for major projects. "Between the water and soil issues, we need to take a little more time to figure out if there's a way to better approach it that both meets all our environmental commitments … as well as the economics."

The three-year project addresses safety and aging infrastructure on the roads and ramps that connect Interstates 35 and 535 and Hwy. 53 in Duluth.

Two major parts of the project — the rebuilding of the Hwy. 53 bridge where it rises over the Lincoln Park neighborhood and the I-535 interchange at Garfield Avenue — were indefinitely postponed last year after contamination discoveries drove the total project cost up to $442 million.

Huston said MnDOT is working to stay within its $343 million budget, though legislators are being asked to consider an increase to finish the project as originally planned.

"We're looking at preservation work on the bridges, to make sure they're not deteriorating anymore, as we work on securing funding," Huston said.

Years of planning went into the project, but Huston said that as more tests were completed, more problems arose.

"A lot can happen between drill holes. I've seen it time and time again," he said. "We developed pretty extensive heat maps and analysis — it's unbelievable."

Some construction will start this fall, though traffic will likely not be affected until next year.

"We are eager for the work to happen because we understand that this project is important for our residents and tourists," Noah Schuchman, the city of Duluth's Chief Administrative Officer, said in a statement. "The city would like to thank MnDOT for the great care and concern that they are bringing to this project and to our community."

Lincoln Park neighborhood advocate Shannon Laing said business owners she talked to on Wednesday found a silver lining in the delay.

"It gives us another year to be as prepared as possible for this," said Laing, community development director for area nonprofit Ecolibrium3. "This is a project that needs to get done, and we want it done well. If it means it has to be pushed out that's what it means."

The delay may also help take the pressure off a busy construction season planned in Duluth. The last year of downtown Superior Street reconstruction starting this spring will coincide with an overhaul of the Lake Avenue bridge and a grip of city road projects backed by the new half-percent sales tax increase.

"We're taking a big piece of that away on I-35," Huston said.