In this April 24, 2020, file photo, a woman wearing a protective mask boards a Massachusetts Bay Transportation Authority's Green Line trolley on Commonwealth Avenue in Boston. Credit: Michael Dwyer / AP

BOSTON — The project to extend the Massachusetts Bay Transportation Authority’s Green Line to Medford has been delayed by five months, the project manager said.

Project Manager John Dalton told the authority’s Fiscal and Management Control Board on Monday that schedule pressure has been caused by about 130 change orders to the original construction plan, delays caused by COVID-19, and unpredictable site conditions such as buried objects, the Boston Herald reported.

Dalton told board members that the project is about 80 percent complete.

The opening has been delayed from December of this year to around May 2022.

Dalton told the board that the $2.3 billion project is in a “very solid financial position.”

Meanwhile, the Union Square branch is ahead of the Medford branch, with 100 percent of its track in place as well as vehicle maintenance facilities, and is expected to be completed by the end of this year.

Steve Poftak, the general manager of the T, said Somerville and Cambridge will now not have to contribute future funds to the project thanks to federal American Rescue Plan money, as well as “careful management of this project.”