In December 2024, the U.S. Environmental Protection Agency (EPA) published the proposed National Emission Standards for Hazardous Air Pollutants for the Polyether Polyols Production Industry (40 CFR Part 63 Subpart PPP) Risk and Technology Review (RTR). The proposal provides a clear signal of how EPA is redefining expectations for air toxics compliance under the Clean Air Act.
The proposal is driven by EPA’s determination that residual risk associated with ethylene oxide (EtO) emissions remains unacceptable under Section 112(f). However, the implications of Subpart PPP extend beyond EtO. The proposed revisions reflect a broader regulatory shift in how compliance is evaluated, enforced, and demonstrated.
EPA had identified December 2025 as the anticipated finalization date for the Subpart PPP RTR in its Unified Agenda, but that schedule has since slipped, and the timing of a final rule remains uncertain.
From Prescriptive Requirements to Demonstrated Performance
Historically, Maximum Achievable Control Technology (MACT) compliance has focused heavily on design-based requirements and prescriptive work practices. Like other recently issued RTR standards, under the proposed Subpart PPP revisions, EPA places increased emphasis on demonstrated, ongoing performance. Compliance credibility is expected to be supported by recurring performance testing, continuous or semi-continuous monitoring, electronic reporting, and documented corrective actions.
Elevated Emission Pathways and Monitoring Expectations
Several elements of the proposal illustrate this shift. Continuous fenceline monitoring is introduced, along with mandatory response obligations when action levels are exceeded. Heat exchanger leaks and EtO bearing wastewater are elevated as priority emission pathways, each with specific monitoring and work practice requirements. Leak detection and repair (LDAR) programs and other fugitive emissions controls are expected to face increased scrutiny, particularly with respect to data traceability, quality assurance, and auditability.
Electronic Reporting and Compliance Transparency
The proposal also reinforces EPA’s move toward standardized electronic reporting. Increased reliance on the Electronic Reporting Tool (ERT) and the Compliance and Emissions Data Reporting Interface (CEDRI) reduces flexibility in explaining deviations while increasing transparency and comparability across facilities. Standardized datasets enable cross facility analysis and support more targeted enforcement strategies.
Continuous Control and Evidence Generation
The removal of affirmative defense further underscores EPA’s expectation of continuous control, including during non-routine operating conditions. Five-year performance testing requirements, when combined with continuous monitoring obligations, push facilities toward ongoing evidence generation rather than periodic demonstrations of compliance. Credibility is increasingly demonstrated through test results, monitoring data, fenceline outcomes, and documented corrective action records.
Broader Implications for MACT and RTR Programs
Taken together, these changes suggest that Subpart PPP is evolving into an outcome-based rule rather than a purely prescriptive MACT standard. When considering similar performance-based requirements of prior RTR rules including Refinery MACT and the Hazardous Organic National Emission Standards for Hazardous Air Pollutants (HON), EPA appears to be positioning fenceline monitoring and performance-based demonstrations as a model for all future chemical sector RTR programs.
Looking ahead, changes in administration may affect timelines, scope, or implementation schedules. However, delays or adjustments are more likely than a full reversal of this performance focused regulatory approach.
For regulated facilities, the message is increasingly clear. Compliance will be defined not only by what controls are installed, but by what can be demonstrated through defensible data over time.
Further Insight
As EPA continues to shift toward performance-based compliance and outcome driven enforcement, facilities subject to Subpart PPP will need to evaluate not only whether controls are in place, but whether compliance can be demonstrated consistently through defensible data.
For #FurtherInsight on Subpart PPP, ethylene oxide risk management, or broader MACT and RTR developments, contact EDGE Engineering & Science.