Dan Gilbert's team has been quietly working on a deal for one of the most perplexing and environmentally challenging properties available for redevelopment in Detroit: the city-owned former Uniroyal Tire Co. factory site on the east riverfront.

Five sources familiar with the negotiations who were not allowed to speak publicly about them confirmed the discussions to Crain's. A sixth, Steve Hoin, senior geologist with the Michigan Department of Environmental Quality, said he met with Gilbert representatives this spring to discuss the site.

"The discussion focused on site issues that might impede development and their interest in that issue," Hoin said.

There is no deal finalized, sources said. But if Gilbert strikes one for the Uniroyal property, the site across from Belle Isle would easily be the most daunting — and largest — he and his team have added to their development pipeline during the real estate and mortgage mogul's seven-year buying and building spree in and around downtown Detroit. It would also plant a large development flag farther outside downtown than his efforts have previously ventured.

Hoin said he had a May 24 meeting with Steve Ogden, vice president of state and local government affairs for Gilbert's Detroit-based Bedrock LLC real estate development, ownership, management and leasing company; John Olszewski, vice president of construction; and Kumar Kintala, director of development.

One of the sources said serious talks began in 2015 between the two sides. There have also been other developers who have had talks about the site in the last couple years, another source said, adding that a deal is not finalized.

The discussions about the 43-acre site are between the city and Bedrock.

One of the sources said a mixed-use development is envisioned for the site, while another said it's in line with the 2,000 residential-unit plan envisioned by the Pittsburgh-based development group tapped 13 years ago during the Kwame Kilpatrick administration to build on the property.

Whitney Eichinger, vice president of communications for Gilbert's Rock Ventures LLC, said the company does "not comment on rumors and speculation."

It would be the latest riverfront project tied to Gilbert, the founder and chairman of Quicken Loans Inc. and Rock Ventures LLC.

His team is in negotiations with General Motors Co. to do a mixed-use project on a 10-acre parcel east of the automaker's Renaissance Center headquarters, and has generally said he is interested in riverfront development.

The GM site doesn't have the challenges the Uniroyal property does, however.

Only a little more than one-third of the site has been cleared of contaminants resulting from more than a century of industrial use. Most recently, 1941-78, it was home to a Uniroyal tire manufacturing plant and a Michigan Consolidated Gas Co. coal-gasification plant. The city bought the land from Uniroyal in 1981 for $5 million and spent $3.6 million more razing structures and clearing the site.

Remediation of just the western 15-acre parcel cost Detroit-based DTE Energy Co., which now owns MichCon; E.I. du Pont de Nemours & Co.; and Michelin USA Inc. around $35 million. The Michigan Department of Environmental Quality assigned the cleanup cost to DTE, Michelin, du Pont and London-based Enodis plc in 2006.

In 1986, Mayor Coleman Young toured the site with Donald Trump, who pondered a development there.

The city had tapped Pittsburgh-based C.J. Betters Enterprise, affiliated with Bettis/Betters Development LLC, to oversee a planned redevelopment that, at the time, had a projected price tag of $500 million with 2,000 residential units and retail space.

Among the investors in that group was Jerome Bettis, the Detroit native and Pittsburgh Steelers running back until he retired in 2005, the year after Bettis/Betters was awarded the redevelopment contract.