SUMMARY OF ARGUMENT The modification provisions of the Clean Air Act Amendments of 1970 and 1977 (1970and 1977 CAA) reflect a specific Congressional decision to limit the period within which existingsources could continue to operate without complying with new source review (NSR)requirements. 1 Congress decided to reconcile economic growth with achieving and maintainingair quality by subjecting all pollution increasing changes – modifications of existing sources andadditional new sources – to identical new source requirements. Congress afforded existing sourcesa limited grace period because existing sources’ limited useful lives would force them to eitherupgrade or shutdown. EPA’s rules illegally substitute an extended immunity from NSR for thestatutory regime of equal treatment of all emissions increasing projects. The statutory definition of modification already establishes that energy efficiencyenhancements that reduce emissions below current levels do not trigger NSR. See 42 U.S.C. §7411(a)(4). EPA’s rules allow projects that