March 18, 2026

Stationary Turbine Final Rule Much Weaker Than Proposed

On January 15, 2026, EPA finalized amendments to the stationary gas and stationary combustion turbine new source performance standards. [91 FR 1910] Impacting Part 60, Subparts GG and KKKK, and establishing a new Subpart KKKKa, the final rule is substantially more lenient than the 2024 proposal. [89 FR 101306] Estimated annual nitrogen oxide (NO_X) emission reductions stand potentially as low as 15 tons by 2032 [91 FR 1962], a 177-fold decrease from the proposal’s estimate of 2,659 tons[89 FR 101350]. Additionally, the agency decided the extra $79 million in facility compliance cost (the proposal’s $166 million [89 FR 101350] minus the final rule’s $87 million [91 FR 1967]) outweighed the $340 million that could have been saved by improved public health [89 FR 101354]. In fact, the economic cost of harm to human health caused by fine particles and ozone will no longer be considered in future EPA rules. [91 FR 1964]

The most significant portion of the rule creates a new Subpart KKKKa, which :

Establishes subcategories and NO_X emission limits based on size, utilization, design efficiency, and fuel for stationary combustion turbines that commenced construction, modification, or reconstruction after December 13, 2024; and
Creates a stationary temporary combustion turbine subcategory with reduced monitoring, administrative, and permitting requirements.

Subparts GG and KKKK

Subpart GG contains only a few notable changes, including: an alternative to comply with Subpart KKKKa; an exemption if a turbine is subject to Subpart Da (NSPS for electric utility steam generating units), KKKK, or KKKKa; an exemption from the sulfur dioxide standard if the turbine is subject to Subpart J or Ja (NSPS for petroleum refineries); and electronic reporting via EPA’s compliance and emissions data reporting interface (CEDRI).

In addition to the changes seen for Subpart GG, Subpart KKKK also contains exemptions for military combustion turbines and for combusting byproduct fuel. One change was made to the NO_X emission limits: for combustion turbines bypassing the heat recovery unit that have a heat input at peak load >50 MMBtu/h, the NO_X standard is 25 ppm at 15% O₂ or 150 ng/J of useful output. [Subpart KKKK, Table 1]

Subpart KKKKa

Subpart KKKKa applicability is similar to Subpart KKKK but with additional exemptions. The NO_X standards apply at all times, including during startup, shutdown, and malfunction; however, the limits vary depending on whether the source chooses to comply with the input- or output-based standard in Subpart KKKKa, Table 1.

Though Subpart KKKKa contains reduced monitoring, administrative, and permitting requirements for temporary units [§60.4331a], the NO_X standard for such units is not always less stringent than for non-temporary units. On the contrary, the NO_X standard for temporary units is often lower than for other units. For example, temporary turbines with a base load rated heat input >50 MMBtu/h have an input-based standard of 25 ppm at 15% O₂ or 40 ng/J. Compare this to the standard for new, non-natural gas-fired units with a base load rated heat input >50 MMBtu/h and ≤850 MMBtu/h, which is 74 ppm at 15% O₂ or 120 ng/J. [Subpart KKKKa, Table 1]

A temporary combustion turbine is defined as “a combustion turbine that is intended to and remains at a single stationary source (or group of stationary sources located within a contiguous area and under common control) for 24 consecutive months or less.” [§60.4420a]

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