On April 22, 2026, the US Environmental Protection Agency (EPA) proposed updates to the National Emission Standards for Hazardous Air Pollutants (NESHAP) for the oil and gas sector through 40 CFR Part 63, Subparts HH (Oil and Natural Gas Production) and HHH (Natural Gas Transmission and Storage). The proposed updates include potential changes to how certain emission points are regulated under the Clean Air Act (CAA) and 36 targeted questions for stakeholder input, which EPA has organized into a structured framework to gather feedback and technical data on regulatory approaches, emissions controls, and implementation considerations. The EPA has organized these comment solicitations using indexed identifiers (e.g., “Question 1”, and “Question 2”) to provide a consistent framework for submitting feedback. Written comments are due June 22, 2026.
Trihydro will release three additional articles with an in-depth look at EPA’s proposed changes and their effect on permitting, compliance, and future planning for oil and gas operations. For operators and environmental compliance teams, the most important near‑ term questions include regulatory applicability (which facilities and emission points are covered), how EPA treats major source versus area source status, what the proposal could mean for Title V air permitting, compliance demonstrations, and future control obligations.
These proposed updates are not final. However, facilities should review the proposal against their current emissions inventory and air compliance strategy to identify potential compliance pathways and comment priorities.
Background: What are NESHAP Subparts HH and HHH?
In 1999, EPA published NESHAP to regulate hazardous air pollutant (HAP) emissions from crude oil and natural gas production facilities and from natural gas transmission and storage facilities. These rules, including 40 CFR Part 63 Subparts HH and HHH, are designed to reduce public health risks by controlling emissions of HAP emissions such as benzene, toluene, ethylbenzene, and xylene (BTEX), which are known to contribute to cancer and other serious health effects. Subpart HH and HHH primarily affect glycol dehydrators, storage vessels with HAP emissions, and equipment leaks associated with glycol dehydrators. These rules define which emission sources are regulated, as well as how emissions are monitored, calculated, recorded, and reported. Overall, the regulations also play an important role in determining Title V applicability based on permitted HAP emissions.
Proposed Changes to NESHAP Subparts HH and HHH (and Why It Matters for Oil & Gas Operators, EHS, and Compliance)
Under a CAA Section 112(d)(6) review, EPA is evaluating three areas related to Subparts HH and HHH. These proposed changes include:
1. Updating and clarifying currently regulated emission points to improve clarity and reduce burden for both operators and the agency. Currently regulated sources include:
- Glycol dehydrators and process vents
- Storage vessels with flashing emissions
- Equipment leaks associated with glycol dehydrators
2. Assessing previously unregulated emission points for possible inclusion under Subparts HH and HHH, including:
- Acid gas removal units (AGRU)
- Non-flashing storage vessels
- Transport vessel loading operations
- Process controllers
- Pumps
3. Considering new standards for additional hazardous air pollutants that are not currently regulated under these subparts, including:
- Methanol
- Metal HAPs
EPA’s stated goal of this review is to improve regulatory clarity and modernize compliance approaches while maintaining protection of public health under the Clean Air Act. The proposal emphasizes simplifying emissions calculations, monitoring, and compliance demonstrations, and reducing long‑standing confusion that has complicated compliance for operators and regulators. The focus is on refining definitions, updating compliance pathways, and aligning requirements with current industry practices to make the rules more workable in practice. EPA also identifies potential deregulatory elements, such as alternative monitoring methods and streamlined compliance approaches, that could lower administrative burdens and compliance costs.
As stated in Question 17, EPA is explicitly seeking input on whether these proposed changes achieve their intended effect of simplifying compliance and providing tangible regulatory relief for operators. Additionally, the rules are intended to preserve the underlying MACT framework.
Delve Deeper with our in-Depth Guide to EPA’s Proposed Changes to Subparts HH and HHH
These proposals signal a heightened EPA focus on emission calculation methodologies, compliance demonstration, and regulatory clarity for oil and gas facilities. Trihydro will publish a three additional Delve articles addressing EPA’s proposed updates to NESHAP Subparts HH and HHH, each aligned with a core category open for public comment as described below:
- Part 2 covers proposed permitting and emission calculation revisions affecting major versus area source determinations, updated approaches to BTEX limits, and air quality modeling.
- Part 3 will focus on proposed changes to LDAR and MACT requirements, including the use of Optical Gas Imaging and Appendix K, and how these changes affect compliance demonstrations, monitoring programs, and recordkeeping.
- Part 4 will conclude the series by examining EPA’s requests for comment on methanol, metal HAPs, and submerged filling practices, along with the potential implications for emissions inventories, source classification, and long-term compliance strategies.
