The U.S. Environmental Protection Agency and U.S. Steel Corp. on Wednesday announced a $75 million cleanup and restoration project at the company’s former Duluth steel mill along the St. Louis River.

The project will deal with nearly 700,000 cubic yards of contaminated sediment, some of it on land but most of it in the Spirit Lake area of the St. Louis River estuary off Duluth's Morgan Park neighborhood.

Some of the toxic stuff will be capped where it sits while much of it will be dredged out of the river and placed in three on-land containment cells on the former steel mill site. Officials said the cells will be lined, bermed and capped to keep contaminated material from moving back into the river or groundwater.

Work is expected to begin in 2019 and - as the ecosystem becomes cleaner and the fish become closer to being safe for all people to eat - should help move the St. Louis River estuary closer to being off the list of polluted “areas of concern” across the Great Lakes.

It’s one of the largest aquatic pollution cleanups ever in Minnesota.

“This is a huge milestone toward finally getting this site cleaned up,’’ Erin Endsley, project manager for the Minnesota Pollution Control Agency, told the News Tribune.

The site has been on the federal Superfund list since 1983 due to extensive pollution of coal tar, heavy metals and other toxic contaminants. Millions of dollars of cleanup work was conducted in the 1980s and ’90s at the former steel mill site, but much more pollution was found on land and in the river, leading to drawn-out efforts to reach a cleanup agreement with the company.

Under the deal announced Wednesday U.S. Steel will foot 55 percent of the cost of the sediment effort with the EPA adding the other 45 percent in taxpayer dollars from the Great Lakes Legacy Act aimed at cleaning up historically polluted areas of the lakes.

“Today’s $75 million restoration project with U.S. Steel shows that public-private partnerships can deliver results, in this case, a major step forward in restoring the St. Louis River,’’ said Cathy Step, the EPA’s regional administrator in Chicago, in a statement.

U.S. Steel President David Burritt said in a statement his company is eager to “continue our successful partnership with EPA to address legacy impacts at our former Duluth Works,’’ saying the work will manage contaminated sediments and create new habitat in the estuary.

The announcement comes as the PCA was moving toward a record of decision that would have required U.S. Steel to clean up the contaminated sediment under Superfund laws. But access to the federal Legacy Act funding was an incentive for U.S. Steel to move the project forward faster than if it had proceeded under the traditional Superfund process where the responsible company pays the entire bill, the PCA’s Endsley said.

“We were headed in that direction. But the MPCA has agreed not to pursue an enforcement action against the company as this project now moves forward under the Legacy Act,’’ Endsley said. “There is some public perception that Superfund is polluter-pay while this has a (taxpayer) element. But Congress enacted this program to get these sites cleaned up faster.”

In addition to the dredging contaminated sediment, the cleanup plan also calls for constructing an engineered cap over 100 acres of polluted estuary sediment and creating a new 30-acre sheltered bay for fish and wildlife habitat. The design work is expected to be finished in December.

U.S. Steel’s Duluth Works mill operated from 1916 to 1981 producing coke, iron and steel and was one of the city's largest employers. At its peak during World War II the mill produced 715,000 tons of steel a year. But the steelmaking process also generated tons of hazardous waste and byproducts that ended up polluting the property and adjacent St. Louis River.

Following the discovery of soil and water contamination in 1979 the site was added to the federal Superfund site list. The PCA has been leading site cleanup activities since 1981. More than $12 million already has been spent on cleanup at the site, but additional pollution was found in recent years on land, in a creek that runs through the property, and in the adjacent St. Louis River.

Coal tar is still seeping to the surface of the property. Polyaromatic hydrocarbons (PAHs) and heavy metals are the primary contaminants in the river. PAHs are toxic to aquatic organisms, can cause internal and external tumors on fish and potentially can cause cancer in humans. Heavy metals have similar toxicity effects on aquatic organisms and can cause neurological problems, kidney and liver damage and developmental problems in people if they are exposed to high concentrations. These contaminants are present in moderate to high levels in the Spirit Lake sediment.

The proposed cleanup plan sets technical goals for lowering concentrations of PAHs, lead, copper and zinc to below acceptable levels in the river.

The U.S. Steel Plant Duluth Works Superfund site includes about 500 acres on land and another 100 in the river. Most of the cleanup project was mapped out in a 1989 document from the PCA with cleanup expected to be mostly complete by 1997. A standard review of the project in 2008, as required under the Superfund law, found much more work was needed.

In addition to the sediment cleanup U.S. Steel remains responsible for smaller cleanup efforts still needed on land at the steel mill site, Endsley noted. Parts of the old steel mill site will be available for recreational use while other areas could be available for more intense development.