A multistate coalition of attorneys general and municipal governments is suing the U.S. Environmental Protection Agency over its decision to eliminate the federal greenhouse-gas emissions limit for new fossil-fuel power plants — and Colorado has joined the plaintiff lineup, KDVR reports.

The underlying rule, the Greenhouse Gas New Source Performance Standard (GHG NSPS) under Section 111 of the Clean Air Act, has been rewritten three times since 2015 by successive administrations. Its current form set a numeric CO2 emission rate for new, modified, or reconstructed generating units above a size threshold set in the rule. The repeal removes that federal floor for any future coal or natural-gas plant seeking a construction permit.

What changes for utilities and combustion-byproduct markets

The retirement schedule of the existing U.S. coal fleet carries the largest commercial knock-on effect. Coal-fired generation produces three material streams that move through secondary commodity markets:

• Fly ash — sold as a supplementary cementitious material to concrete producers, where it partly replaces portland cement and cuts clinker demand.
• FGD gypsum — captured by flue-gas desulfurization systems and resold to wallboard manufacturers as a substitute for mined rock gypsum.
• Bottom ash and boiler slag — fed into lightweight aggregate, road base, and roofing-granule supply chains.

If the GHG NSPS repeal holds, removing federal CO2 compliance pressure on new builds makes coal-plant economics less attractive relative to gas and renewables on a marginal-MWh basis. Faster retirements shrink the supply base for these secondary materials at the same time cement and wallboard buyers step up demand for low-carbon inputs under their own decarbonization programs.

Why Colorado's participation matters

The state's participation carries weight beyond coalition size. Colorado's 2019 climate framework, House Bill 19-1261, commits the state to a 50% reduction in greenhouse-gas emissions by 2030 and a 90% cut by 2050 against a 2005 baseline — targets that statute codifies and the state's integrated resource planning process reconciles against for investor-owned utilities.

State-level rules do not depend on the federal GHG NSPS to function, and Colorado's three principal load-serving utilities — Public Service Company of Colorado, Black Hills Energy, and Colorado Springs Utilities — already plan around a near-zero-emission build. Joining the suit preserves the option of a federal backstop if state-level policy weakens under future legislation.

What the litigation resets

Plaintiffs will likely attack the repeal on procedural and substantive grounds — that the EPA failed to justify rescinding the NSPS under the Clean Air Act's "remainder of the section" framework and that the agency ignored record evidence on cost-effective control technologies. Procedural challenges to the rulemaking's public-comment window and administrative record handling are likely follow-ons.

The deciding milestones are:

• The formal filing of the amended complaint and the selection of a forum — venues Democratic AGs have used in past GHG cases include the U.S. District Court for the Western District of Washington and the Northern District of California.
• Any motion for a preliminary injunction or administrative stay that could freeze parts of the repeal during litigation.
• The EPA's filing of its administrative record, which sets the briefing calendar.

Until those dates are on the docket, utilities, coal-combustion-product marketers, and state permitting authorities operate in a regulatory holding pattern on new fossil generation.