Image courtesy of Google Maps.

The long-term lease to develop the former Bayside Expo Center site next to UMass Boston has been signed, with about $235 million expected to flow to the harbor-side campus over the duration of the 99-year deal.

Under the agreement, Accordia Partners and Ares Management Corp. will construct a 3.4 million-square-foot, mixed-use project on the 20-acre parcel. The lease signing was announced jointly Tuesday morning by UMass, the UMass Building Authority, Accordia and Ares.

The parameters of the deal were announced in February when the UMass Building Authority designated Accordia and Area as the developers. Supporters of the project describe it as a “new gateway to UMass Boston” that will connect the Columbia Point campus to the JFK/UMass MBTA station and the nearby harborwalk.

Accordia’s Kirk Sykes and Dick Galvin said in statements that the project’s next phase involves listening to neighbors, faculty and staff at UMass Boston about ways that the project can create shared benefits. The transaction is not expected to close for 24 months, the length of time Ares and Accordia say they need to receive all regulatory approvals.

“The Bayside development is a game-changer for our students and faculty,” UMass-Boston Interim Chancellor Katherine Newman said in a statement. “This agreement moves us one giant step closer to bringing new private sector research partners, internship providers, and job opportunities in construction, retail and services to Columbia Point.”

The Bayside project is not Accordia’s and Ares’ only venture on Columbia Point. The pair last month dropped $110 million on Santander Bank’s 12-acre property at 2 Morrissey Blvd., across Mt. Vernon Street from the Bayside site.

Nearby, work is underway at The Nordblom Co.’s The BEAT, a life science and advanced manufacturing center inside the converted former Boston Globe headquarters, and Center Court Properties is exploring a six-building, 1,774-unit redevelopment of a series of properties between The BEAT and the JFK/UMass station.