The unprecedented shutdown of Boston's Orange Line train service is due in part to "decades of underinvestment" in the MBTA, according to General Manager Steve Poftak, who acknowledged the impending 30-day closure will be "very disruptive" to commuters.

Speaking at a Greater Boston Chamber of Commerce event on Thursday, Poftak was asked by Chamber President and CEO James Rooney how the MBTA got to the point of shutting down an entire service line for a month.

"Part of how we got here is decades, decades of underinvestment. A little over a decade ago, we were investing less than $400 million a year in the MBTA on the capital side. That is not nearly enough," Poftak said.

In recent years the MBTA budget has come in at more than a billion dollars annually. In 2021, the beleaguered transit system got roughly $1.3 billion, an increase of $98 million from the year prior. The 2022 budget funneled another $1.3 billion to the agency, and just last month, Gov. Charlie Baker signed the fiscal year 2023 budget, which included more than $1.7 billion in MBTA funding.

"It is going to take a sustained level of investment in this system to bring it up to the modernized state that our customers deserve and, frankly, that our workforce deserves," he added.

Poftak said the "bold and decisive action" to shut down the line was made to prioritize safety for riders.

Some have questioned if the planned work will actually be completed in 30 days, given recent repairs like the Blue Line service suspension in the spring that extended for several extra days. Poftak said there are contingencies in place to make sure the Orange Line work gets done in the allotted time.

"I don't want to gloss over the fact that we know that this is going to be inconvenient for people. We're doing our best to minimize that inconvenience," Poftak said, adding that the 30-day project will accomplish five years' worth of night and weekend work on the Orange Line.

"I think what you're seeing in this 30-day closure is the realization that the MBTA cannot be modernized in its entirety on nights and weekends," Poftak said.

Track maintenance will be the highest priority during the shutdown, according to Poftak, who said work will be ongoing every day of the week for 24 hours a day. The plans include replacing thousands of feet of rails, updating signal systems and implementing new power substations.

Poftak pushed back on the notion that the work could have been done earlier in the pandemic when ridership was low, saying it's "categorically false" that no one was riding the T.

During the height of the pandemic, MBTA ridership dropped down to just 13% of pre-pandemic figures. Now, it's up to around 57%, according to data compiled by TransitMatters.

The Orange Line shutdown will begin on Friday, Aug. 19 and will end on Friday, Sept. 19 with shuttle buses replacing service.