The veteran developer on Wednesday morning filed a letter of intent with the city for a 600-foot-tall office and condo building that would transform a key piece of the downtown waterfront. The letter is just a procedural step — Chiofaro did not include any images of the proposed tower and is still working out many details — but it starts a new and far more specific phase of planning for a huge project that has long been more about promise than reality.

After seven years of planning and debate, Don Chiofaro is finally ready to propose his signature skyscraper on the site of the Boston Harbor Garage.


“We have an enormous responsibility to the city,” Chiofaro said. “It’s time to allow residents of — and visitors to — Boston the opportunity to enjoy the full potential of Boston’s waterfront.”

More details, including potential designs from architects Kohn Pedersen Fox, will come in the next few months. But Chiofaro’s letter to the Boston Planning & Development Agency outlines the basics of his $1 billion project.

It would feature a single building, reaching up to 600 feet high with 900,000 square feet of space, mostly office and residential and perhaps with a hotel. The precise mix is still to be determined. The bottom two or three floors would be for retail, restaurants, and other “active” uses, according to the plans.

Crucially, the building would take up just half the space on the street that the massive concrete garage now does, opening up a plaza that would run alongside the New England Aquarium’s planned “Blueway” on Central Wharf and, the developer said, better knitting the waterfront together with the Rose Fitzgerald Kennedy Greenway and nearby sections of downtown.

Most of these parameters were ironed out in years of often-contentious negotiations between Chiofaro, the city, the project’s neighbors, and neighborhood groups, leading to rules that were formally signed into Boston’s zoning just last week. Now, they can delve into planning the project itself.


That doesn’t mean there aren’t still hurdles to clear, or concerns about a project that would be far larger than almost anything ever built so close to Boston Harbor.

Two pending lawsuits — one against Chiofaro by the neighbors at the Harbor Towers condominium complex, another by the nonprofit Conservation Law Foundation challenging state approval of the broader downtown waterfront zoning — could yet delay or even derail the project. Last month, a judge ruled that parts of those lawsuits could advance toward trials. Negotiations also continue with the aquarium over parking and other measures to protect the nonprofit organization from losing business during construction.

Those talks will now go on alongside a formal BPDA planning process, with a goal of winning approval in a year to 18 months. Along the way, Chiofaro Co. executive Rob Caridad said, the company may be able to iron out its differences with neighbors and other critics.

“We believe strongly that our interests align, far more than they diverge, with Harbor Towers and CLF,” Caridad said. “We think the best way to advance the conversation is to remove the mystery about what we’re thinking.”

CLF and Harbor Towers, though, said they were skeptical. The environmental group said Chiofaro was proceeding as his own peril.

“Any developer that advances a project based on the [zoning] variances in this current plan does so at their own financial risk,” the group said in a statement. “Developers cannot be allowed to buy their way out of rules protecting public access to and enjoyment of the waterfront.”


A spokesman for Harbor Towers, meanwhile suggested Chiofaro and the city should await results of the lawsuit before moving forward.

“The Superior Court’s decision in October casts significant doubt on whether any project would comply with Massachusetts environmental law,” Harbor Towers spokesman Tom Palmer said. “As long as that legal question remains unresolved, it is premature to try to move forward on a project.”

A spokesman for the aquarium, which at times has described construction of Chiofaro’s tower as an existential threat to its finances, had no comment, but said the nonprofit is moving ahead with its own real estate plans for Central Wharf.

Should he win the needed permits, Chiofaro would have to finance and fill the building with tenants, and he’ll be attempting to do it on the back end of a wave of towers already underway and planned downtown. But the veteran developer — best known for building International Place in the 1980s — is as bullish as ever that he’ll have no trouble doing just that.

“These projects take a long time. There’s a lot of ups and downs,” he said. “One thing won’t change: I think this is probably the best [development] site in the country.”

Tim Logan can be reached at tim.logan@globe.com. Follow him on Twitter at @bytimlogan.