"Potential to emit" means the maximum capacity of a stationary source to emit any regulated pollutant under its physical and operational design. Any physical or operational limitation on the capacity of the source to emit a regulated pollutant, including air pollution control equipment, and restrictions on the hours of operation or on the type or amount of material combusted, stored, or processed, shall be treated as part of its design only if the limitation or the effect it would have on emissions is federally enforceable as a practical matter. Secondary emissions do not count in the determining the potential to emit of a source.
06- 096 C.M.R. ch. 100, § 137