not feasible to prescribe or enforce a standard of performance
(2) For the purpose of this subsection, the phrase “not feasible to prescribe or enforce a standard of performance” means any situation in which the Administrator determines that (A) a pollutant or pollutants cannot be emitted through a conveyance designed and constructed to emit or capture such pollutant, or that any requirement for, or use of, such a conveyance would be inconsistent with any Federal, State, or local law, or (B) the application of measurement methodology to a particular class of sources is not practicable due to technological or economic limitations.