Stationary engines remain one of the most heavily regulated emission sources in the oil and gas, midstream, and industrial sectors. Regulatory requirements continue to evolve at both the federal and state levels, creating new compliance considerations for facility owners and operators.
Recent developments involving EPA’s National Emission Standards for Hazardous Air Pollutants (NESHAP) for Reciprocating Internal Combustion Engines (RICE), ownership considerations for permitted engines, and upcoming New Mexico Ozone Precursor Rule requirements may significantly impact compliance strategies over the next several years. Organizations should evaluate their current engine inventories and compliance programs to ensure they are prepared for these regulatory changes.
NESHAP ZZZZ Status Changes: Relief for Certain Facilities
Facilities that have transitioned from a HAP major source to a HAP area source should evaluate how recent Congressional action may affect engine compliance obligations under the RICE NESHAP (40 CFR Part 63, Subpart ZZZZ). Historically, EPA’s September 10, 2024 rule would have required certain engines to continue complying with major source requirements even after a facility became an area source. However, Congressional action under the Congressional Review Act nullified that rule effective January 2, 2026. As a result, some facilities may now be able to comply with requirements associated with their current source classification rather than historical major source obligations.
Historically, EPA’s September 10, 2024 final rule required certain engines that were previously subject to major source requirements to continue complying with those requirements even after a facility became an area source. This approach created long-term compliance obligations for engines despite a change in facility classification.
However, on June 20, 2025, Congress enacted legislation pursuant to the Congressional Review Act that nullified the September 2024 EPA rule. The congressional action became effective on January 2, 2026.
As a result, facilities that have changed status from a HAP major source to a HAP minor or area source may now be able to comply solely with the requirements applicable to their current source classification rather than continuing to meet historical major source requirements.
Organizations that have undergone source reclassification should evaluate their engine compliance obligations to determine whether monitoring, testing, reporting, and operational requirements have changed under the revised regulatory framework.
Third-Party Owned Engines: Who Is Responsible for Compliance?
A common area of confusion arises when an engine operating at a facility is owned and operated by a third party but is included on the facility’s air permit.
When evaluating compliance responsibilities, one of the first questions to ask is: Is the engine specifically identified as an emission unit on your permit?
In many air permits, compliance obligations are assigned to the permittee regardless of equipment ownership. Therefore, if a third-party owned engine is included as a permitted emission unit, the permittee may remain responsible for demonstrating compliance with applicable permit conditions, regardless of who owns or operates the equipment.
These responsibilities may include:
- Monitoring requirements
- Emission testing obligations
- Recordkeeping requirements
- Reporting obligations
- Operational limitations
- Compliance certifications
Failure of a third-party contractor to meet permit requirements does not necessarily relieve the permittee of regulatory liability. Operators should consider incorporating compliance responsibilities, testing requirements, record retention obligations, and access to operational data into equipment lease or service agreements when third-party engines are present on a permitted site. Reviewing permit language and understanding ownership versus compliance responsibility can help prevent enforcement risks and ensure accountability for all equipment operating under the permit.
New Mexico Ozone Precursor Rule: When Is Your Engine Considered “New”?
One of the more frequently misunderstood aspects of New Mexico’s Ozone Precursor Rule (20.2.50 NMAC) is determining whether an engine is considered “new” or “existing” for compliance purposes. The Ozone Precursor Rule became effective on August 5, 2022. For engines subject to the rule, an engine’s status is not necessarily based on when it was manufactured or purchased. Instead, operators should understand when the engine was first constructed within the state of New Mexico.
Under the New Mexico Ozone Precursor Rule, an engine’s classification as new or existing is tied to the rule’s definition of construction in 20.2.50.7(C)(7) NMAC. As a result, engines first constructed in New Mexico after the August 5, 2022 effective date may be subject to different requirements than engines that were already present in the state prior to that date.
An engine is considered new under the New Mexico Ozone Precursor Rule when it is first constructed (as defined in 20.2.50.7(C)(7) NMAC) in New Mexico after the rule’s effective date. As a result, engines brought into New Mexico from another state may be subject to different requirements than engines that were already in New Mexico prior to August 5, 2022.
This distinction is particularly important for operators that relocate equipment between states. Moving an engine into New Mexico may result in the engine being treated as a newly affected engine for purposes of determining applicable Ozone Precursor Rule emission standards and compliance obligations.
Considerations for Rented Equipment
Operators utilizing rental engines should work closely with equipment providers to understand the engine’s operating history within New Mexico. Specifically, rental companies should be able to provide documentation demonstrating when the engine was first constructed in New Mexico.
This information can be critical when determining which Ozone Precursor Rule requirements apply and ensuring compliance with applicable emission standards. Maintaining records that document an engine’s operational history can help support applicability determinations during inspections, audits, and permitting activities.
When evaluating engine compliance under the New Mexico Ozone Precursor Rule, operators should consider:
- Relocating engines into New Mexico can affect applicability and compliance obligations.
- Rental companies should provide documentation regarding when an engine was first constructed in New Mexico.
- Maintaining accurate engine history records can simplify compliance evaluations and support regulatory determinations.
Key Takeaways for Operators
Engine compliance continues to evolve as federal and state regulations are updated. Facilities should consider reviewing engine inventories, permit obligations, and long-term compliance plans to identify potential risks and opportunities.
Particular attention should be paid to:
- Facilities that have changed from HAP major source status to area source or minor source status
- Third-party owned engines included on existing permits
- Engine applicability determinations under the New Mexico Ozone Precursor Rule
- Documentation supporting when rental or relocated engines first entered service in New Mexico
Early planning can help facilities avoid costly compliance issues while positioning operations for future regulatory developments.
Whether you are evaluating RICE NESHAP applicability, managing third-party equipment on a permit, or preparing for upcoming New Mexico engine requirements, Trinity Consultants can help. Our team assists clients with engine compliance evaluations, permit reviews, emissions testing strategies, regulatory applicability analyses, and compliance planning to support both federal and state regulatory requirements.
If you would like to discuss Engine Compliance, please email Michael Brown in Trinity’s Albuquerque Office or call 505.266.6611.
