On March 13, 2026, EPA Administrator Lee Zeldin signed final amendments to the National Emission Standards for Hazardous Air Pollutants (NESHAP) for the Polyether Polyols Production (PEPO) source category, codified at 40 CFR Part 63, Subpart PPP. The final rule addresses the second technology review under Clean Air Act (CAA) section 112(d)(6), reconsideration issues from the 2014 rulemaking petition, and establishes new ethylene oxide (EtO)-specific emission standards that will require most facilities to undertake significant process reviews and capital investments. The rule was originally proposed on December 27, 2024 (89 FR 105986), and as of December 2025, EPA identified 23 PEPO production facilities subject to these standards under NAICS Code 325199.
While this final regulatory action differs from the proposal in several key areas, this finalized standard remains more restrictive than its predecessor. Understanding those differences is critical to building an accurate compliance roadmap.
Significant Statutory Authority Shift
The December 2024 proposal pursued EtO controls under both CAA section 112(f)(2) (residual risk review) and CAA section 112(d)(6) (technology review). In response to public comments and court decisions, the final rule instead finalizes EtO-specific standards solely under the technology review, which authorizes EPA to revise standards based on developments in practices, processes, and control technologies. In the preamble, EPA acknowledges that it does not have statutory authority to conduct more than one residual risk review under CAA section 112(f)(2).
New EtO-Specific Standards
The most consequential aspect of this rulemaking is the the creation of entirely new EtO-specific requirements spanning multiple emission source categories. For facilities with EtO in their operations, virtually no unit operation is left untouched. From process vents to wastewater, the details of each standard will determine your compliance strategy and cost exposure.
EtO Process Vents
A new definition targets any process vent containing ≥1 ppmv undiluted EtO where combined vents emit ≥100 lb/yr EtO uncontrolled. Facilities have several reduction options for reduction of EtO in the process vent, including:
- Must reduce EtO by ≥99.9% by weight, OR
- Must reduce EtO to <1 ppmv per vent or <100 lb/yr combined, OR
- Route to a compliant flare.
Compliance pathway selection, non-flare device vs. flare, involves significant trade-offs in capital cost, monitoring burden, and operational flexibility. Determining the right approach requires a detailed engineering evaluation.
EtO Storage Vessels
Facilities must now address storage vessels where stored liquid contains ≥1.0% EtO by weight. New control requirements apply (see above), including specific work practice standards for degassing and planned maintenance activities that many facilities have not had to address before.
EtO Equipment
LeaksNew equipment leak definitions apply to equipment in contact with fluid that is ≥1.0% EtO by weight. Monthly valve monitoring and quarterly connector monitoring is required, with a tightened 100 ppmv leak definition and very limited flexibility for delayed repair. These are significant LDAR program upgrades for most facilities. Similarly, monthly monitoring for pumps in light liquid service is required with a 500 ppmv leak definition.
EtO Heat Exchange Systems
Monthly monitoring requirements apply to heat exchangers in EtO service using a specific EPA-prescribed method, and a new leak definition has been established. If your facility has not previously been subject to these requirements, understanding the monitoring protocol and analytical requirements is an important early step.
EtO Wastewater Streams
New requirements target wastewater with total annual average EtO concentration above 10 ppmw. Facilities must reduce EtO to <1 ppmw, or comply with Group 1 wastewater controls under the HON.
Updates to Non-EtO PEPO Standards
Batch Process Vents
The Group 1 threshold has dropped to 10,000 lb/yr nonepoxide organic HAP, a significant reduction that will pull additional vents into control requirements. The flow rate threshold has also been eliminated, changing how applicability is determined. Facilities should audit all batch vents against the new threshold.
Storage Vessels
The Group 1 capacity threshold has been cut to 38 m³ (10,000 gal) for vessels with sufficient vapor pressure (≥6.9 kPa), and new hardware requirements apply to internal floating roof vessels. Facilities should re-evaluate their vessel inventories, as many previously exempt tanks may now require controls.
Equipment Leaks (General) & Performance Testing
The general valve leak definition for all valves in gas/vapor or light liquid services has been tightened considerably, from 500 ppmv to 100 ppmv, a change that will affect LDAR programs at most PEPO facilities regardless of EtO use. Additionally, recurring performance testing requirements apply to process vents, and a previously available compliance option of design evaluation has been eliminated. This has direct implications for operational planning and testing budgets.
Flares and Closed Vent Systems
Significant new continuous monitoring requirements, operational standards, and formal flare management plans are required, including specific electronic reporting obligations. Pressure-assisted multi-point flares face additional monitoring and operational requirements.
Carbon Adsorbers & Additional Sources
Updated and additional carbon adsorber design, monitoring and testing requirements have also been included. The rule also extends new emission standards to additional equipment categories, along with revised work practice standards for maintenance vents, and startup/shutdown. The addition of butylene oxide to the list of known organic HAP under Table 4; processes after epoxide polymerization using butylene oxide are no longer exempt.
Notable Items NOT Finalized
While EPA finalized many changes, several high-profile proposed provisions were ultimately not included in the final rule. This includes some that generated significant industry concern during the comment period:
- The proposed second residual risk review under CAA §112(f)(2) was NOT finalized.
- The proposed fenceline monitoring work practice standard (EtO monitoring at 0.2 µg/m³ action level) was NOT finalized.
- The proposed removal of the TRE index value concept for continuous process vents was NOT finalized; the current definition is retained.
- The proposed removal of THF-specific thresholds (50 ppmv and 0.005 scmm) was NOT finalized.
- No EtO specific compliance timelines were finalized.
Compliance Timeline
Key compliance deadlines to be aware of:
- Existing affected sources: 3 years from Federal Register publication for CAA §112(d)(2), (3), (6), and 112(h) requirements.
- New affected sources (construction/reconstruction after December 27, 2024): Upon publication or startup, whichever is later.
- Electronic NOCS and CEMS evaluations: 60 days after publication.
- Electronic periodic reports and flare management plans: 3 years after publication.
These changes will require PEPO facilities to carefully evaluate their EtO service equipment and processes, assess new control requirements, and plan for significant capital and operational investments. Note that the final rule is based on the prepublication version signed on 03/13/2026; final Federal Register text should be reviewed upon official publication. Trinity Consultants will be hosting a complimentary webinar to review these changes on April 23rd, 2026 from 11AM-12PM CT.
If you have any questions or need help evaluating how these amendments affect your facility, please feel free to reach out to Gina Driscoll or Ryan Mayces.
