This action pertains to EPA’s federal rules for state implementation plans (SIPs) at 40 CFR part 51.160-164, which apply to the preconstruction permitting of minor sources and minor modifications by state and local air pollution agencies. Most of these New Source Review (NSR) rules have been unchanged for more than 40 years. The purpose of this rulemaking would be to bring the older rules as they pertain to such sources and modifications up to modern standards, improve the accountability of the minor NSR program to address the underlying requirements of the Clean Air Act, and address minimum requirements for consistent implementation while continuing to allow agencies flexibility in some areas of their program.