Ald. Brian Hopkins (2nd) is demanding that Mayor Rahm Emanuel explain why he wants to sell a fleet maintenance facility site on prime riverfront land in the North Branch Industrial Corridor to a developer who is not the highest bidder.

Emanuel announced earlier this year that mega-developer Sterling Bay had agreed to pay the city $104.7 million — $133.53 per square foot — for the lucrative site near the Chicago River, where city vehicles now are maintained.

The deal also requires Sterling Bay to build a new city maintenance facility in Englewood.

What Emanuel failed to mention — and Hopkins revealed — is that Sterling Bay was not the highest bidder. ONNI Group offered $115 million for the prime piece of property.

“There may be solid, rational justification for choosing the second-highest bidder. But, that needs to be explored. Ten million dollars isn’t anything to leave on the table for no reason,” Hopkins said Tuesday.

“We’ve got a community meeting scheduled Thursday. Representatives of the Planning Department will be on hand. They will tell people why they are recommending the second-highest bidder at a cost of approximately $10 million left on the table. We’re gonna hear what those reasons are, then make a determination on the legitimacy of the justification.”

Hopkins said he was equally troubled by the fact that the sale of the North Side site to Sterling Bay was “not listed on the agenda” at Monday’s meeting of the City Council’s Housing Committee.

Instead, it was part of an item described on the agenda as “an ordinance approving the acquisition of City Colleges property at 6800 S. Wentworth.”

That’s the proposed site of the new fleet maintenance facility that Sterling Bay is supposed to build to replace the North Side facility.

“I felt that was highly inappropriate and would open us up to accusations that there was an attempt to sneak this through,” said Hopkins, who deferred the matter.

“That’s anything but transparent. That’s not the way to conduct business when there’s already been great skepticism expressed by the community regarding what’s gonna happen in the former PMD area — not just the fleet center site, but the surrounding area as well.”

Planning and Development spokesman Peter Strazzabosco said the city’s decision to bypass the highest bidder was “based on the guidance of a nationally-recognized real estate broker.”

The city chose the bid “with the fewest contingencies, elimination of market and transactional risk, and a very short and predictable closing period, which will provide more security for Chicago’s taxpayers,” he wrote in an email.

ONNI’s higher bid was “dependent on variables that have yet to be determined over an extended time period and could be subject to significant change, purchase price risk and negotiation,” Strazzabosco said

“The city chose the bid that offers security and efficiency versus unknowns and indefinites,” Strazzabosco wrote.

Sterling Bay and its managing principal Andy Gloor have made more than $50,000 in campaign  contributions in recent years, including $7,550 to Emanuel.

Other beneficiaries have included Aldermen Proco Joe Moreno (1st), Patrick Daley Thompson (11th and George Cardenas (12th) and the ward organizations of Aldermen Danny Solis (25th) and Walter Burnett (27th).

Hopkins’ questions have the potential to throw a monkey wrench into Emanuel’s plan to build a $95 million public safety training campus in West Garfield Park to replace Chicago’s cramped and antiquated police and fire training academies.

The Community Development Commission and the City Council’s Zoning committee have authorized the city to acquire the 30.4 acre West Garfield Park site at 4301 W. Chicago Ave.

But, the two-building training campus will be bankrolled, in part, by proceeds from the sale of the fleet maintenance facility site near the Chicago River on the North Side.

Without that transaction, the whole thing falls apart — or at least gets held up.

Two months ago, the City Council seized what Hopkins called a development opportunity not seen since the Great Chicago Fire.

The 46-to-2 vote paved the way for 760 acres of protected North Side industrial land to be opened to residential and commercial use, despite lingering concern about a shortage of park space and infrastructure to accommodate an avalanche of new residents that nobody at City Hall is prepared quantify.

On Tuesday, Hopkins reiterated those concerns.

He was referring to the fact that Sterling Bay has targeted Amazon’s second North American headquarters as the anchor tenant for a $10 billion mixed-use, riverfront development on land it’s assembling in Lincoln Park and Bucktown that includes the old Finkl Steel plant.

Together with the fleet maintenance facility, Sterling Bay’s managing principal Andy Gloor hopes to put together nearly 100 acres for the project it calls “Lincoln Yards.”

“We’ve had a process now going on two years. People have attended these meetings … looking for assurances that the things they want to see in this redevelopment are going to be there. They don’t feel that they’ve gotten those reassurances,” Hopkins said.

“I see it as my job to deliver those reassurances. And I’m gonna use this moment in time to make sure we have a commitment for the things the neighborhood is asking for: open space, park land, transportation improvements.”