As many as 6,000 people could work and 800 of them could live on a massive riverfront development triggered by Mayor Rahm Emanuel’s plan to open 760 acres of protected industrial land to residential and commercial use in the North Branch corridor.

A 310-unit residential tower, three shorter office buildings with 1.2 million square feet of commercial space and 4.5 acres of open space with a picturesque walkway along the Chicago River are planned for the site owned by Tribune Media at 640-to-740 W. Chicago Ave.

A long-awaited zoning application filed this week by Tribune Media and Riverside Investment and Development would pave the way for a $700 million project that would pay millions of dollars in fees for the land being lost to industrial use.

Riverside CEO John O’Donnell said Thursday he envisions the “once-in-a-lifetime” project as a mecca for the West Coast techies Emanuel covets.

“We sent the team of people to the West Coast, Silicon Valley and San Francisco to try to see what the more mature tech firms were doing. We tried to adapt what they’re looking in terms of a very robust amenity package, open space for meetings, terraces and live, work, play where they’ll be. Plenty of food service as well as fitness and residential on site,” O’Donnell said.

“It really is [for] companies seeking to recruit a younger workforce because this site is dead-center to all of the emerging neighborhoods as well as having physical characteristics [that are] unmatchable. … Since there are bridges approaching the river, we could put parking … 20 or 30 feet below street level, then have a platform [with] park land that would cover the seven acres.”

This rendering shows some of the buildings planned for a six-acre parcel of land at 700 West Chicago Avenue. | Goettsch Partners

The plan calls for developers to demolish a vacant industrial building once used as a Tribune distribution center.

A 450,000-square-foot office building and 310-unit residential tower with parking for 540 vehicles and 50 bikes would be built first. Two more office buildings would follow once tenants are lined up and leases are signed.

The zoning application asks for “flexibility” to devote up to 40 percent of the seven acres to residential space, even though only 20 percent is planned.

O’Donnell said Thursday he is “out looking for” prospective tenants, but wouldn’t identify prospects.

“I’m hoping that a number of them come from outside the city. [But] people from the West Coast don’t really talk to you unless you have zoning in place,” he said.

The project is being financed for now with “Tribune Media land and our cash,” O’Donnell said.

“When we land a tenant, then we’ll solicit financing. I don’t anticipate it being a problem,” he said. “I just can’t think of anything quite like this. It’s not on the fringe of anything. It’s dead-center.”

This residential tower along the Chicago River would be joined by three office towers on a six-acre parcel at 700 W. Chicago Ave., according to the plan by Riverside Investment & Development. | Goettsch Partners

In mid-July, the City Council signed off on North Branch guidelines and agreed to impose three kinds of developer fees: for parks and infrastructure improvements; industrial development elsewhere in the city; and development of retail corridors in impoverished South and West Side communities.

That set the stage for what local Ald. Brian Hopkins (2nd) called a development opportunity not seen since the Great Chicago Fire. But there were lingering concerns about a shortage of park space and infrastructure to accommodate an avalanche of new residents.

Lincoln Park Ald. Michele Smith (43rd) also accused the city of settling for “a fraction” of what the opportunity was worth to firms salivating to develop land along the Chicago River.

On Thursday, O’Donnell acknowledged that two of the seven acres he plans to develop near the Tribune’s Freedom Center printing facility are in a former planned manufacturing district and that zoning “would have to be modified,” triggering millions of dollars in fees.

Density fees would be triggered as well, but only “if we had a tenant that wanted more density,” he said.

As for Smith’s concerns about the strain on infrastructure, O’Donnell said it’s unfounded — at least in this case.

Some projects planned by the city “would alleviate that a lot,” he said, such as widening the Chicago Avenue bridge.

“There’s a private access road the city has planned. … There will be plenty of bike parking. We have within a 10 minutes’ walk basically almost all of the L tracks, L stations. We’ll run shuttle buses to both the L’s as well as to the train stations.”

Pressed for details on the “access road the city has planned,” O’Donnell said: “There’s an access road that goes to the Tribune site, but I’d rather not talk about that. There’s nothing determined there that I can really talk about.”

The North Branch corridor of the Chicago River is expected to be transformed over the next two decades after the City Council recently removed zoning barriers that kept out residential development. | Photo provided by City of Chicago