On October 15, 2021, the United States Environmental Protection Agency's (EPA) Region 1 Acting Administrator signed a Memorandum of Agreement (MOA) between the Massachusetts Department of Environmental Protection (MassDEP) and EPA Region 1 regarding existing affected sources subject to Clean Air Act (CAA) sections 111(d) and/or 129 Federal Plan requirements. Subsequently, the MOA became effective upon signature of the MassDEP Commissioner on November 9, 2021. This document is informing the public of the MOA and making a copy of the document accessible.