text: "New Source Review" (NSR) refers to a permitting program whose basic requirements were established in 1977 as Parts C and D of Title 1 of the Clean Air Act.1 The purpose of the program "is to ensure that when new sources are built or existing sources undergo major modifications: (1) air quality improves if the change occurs where the air currently does not meet federal air quality standards; and (2) air quality is not significantly degraded where the air currently meets federal standards."2 The NSR program attempts to achieve its mission by requiring best available control technology (BACT) or lowest achievable emissions rate (LAER) technology be installed when new units are built or when major modifications are made to existing plants that would lead to a significant increase in emissions.