March 19, 2026 - On Jan. 26, 2026, EPA disapproved Colorado’s revision to its regional haze State Implementation Plan (SIP), concluding that the plan’s enforceable closure date for a coal?fired electric generating unit, Nixon Unit 1, could violate federal or state takings law.

Colorado submitted its regional haze SIP revision to EPA in May 2022. The revision included 13 voluntary source closure dates, including an enforceable closure date for Nixon Unit 1, a coal-fired electric generating unit owned by Colorado Springs Utilities (CSU). CSU had voluntarily requested in 2020 that Colorado include the Nixon Unit 1 closure date in its SIP revision. However, in March 2025, just a few months before EPA’s deadline to approve or deny Colorado’s SIP revision, CSU rescinded its consent to close Nixon Unit 1, citing unexpected changes in circumstance.

When drafting regional haze SIP revisions, states may rely on enforceable source closure dates when determining how to make reasonable progress toward national haze reduction goals. Companies that own emissions sources — such as fossil-fueled power plants — often volunteer their expected source closure dates for inclusion in regional haze SIPs so they can avoid having to adopt stricter, less cost-efficient emissions controls.

This quick take describes the Regional Haze Rule and Colorado’s submitted SIP revision, summarizes EPA’s proposed partial disapproval that became a final full SIP revision disapproval, and highlights some of the legal arguments raised by commenters against EPA’s proposed disapproval. It also looks ahead to how EPA may raise similar takings arguments to reject other states’ SIPs.