MassDot will officially blow a 2014 deadline to offset Big Dig environmental impacts after delaying the Green Line Extension to Somerville and Medford.


To comply with the Clean Air Act and avoid a lawsuit from the Conservation Law Foundation, MassDOT must implement an alternative air-quality improvement plan. It mentioned retrofitting diesel trains as one possible plan.


“MassDOT will continue to work with the Department of Environmental Protection and the public over the next several months to develop appropriate air-quality mitigation that is required to accommodate the delay,” MassDOT spokes-man Adam Hurtubise said in a statement.