Final Updates to the Chemical Manufacturing Area Source Rule

Posted: April 16th, 2026

Author: Philip Crawford

On April 1, 2026, the U.S. Environmental Protection Agency (U.S. EPA) finalized changes to the National Emission Standards for Hazardous Air Pollutants (NESHAP) for Chemical Manufacturing Area Sources (i.e., CMAS, codified at 40 CFR Part 63, Subpart VVVVVV). U.S. EPA made changes to the rule by adding generally available control technology (GACT) standards according to Clean Air Act (CAA) Section 112(d)(5) and as part of a CAA Section 112(d)(6) technology review.

U.S. EPA did not finalize the proposed “Chemical Manufacturing with Ethylene Oxide” source category and associated GACT standards. U.S. EPA stated that it needs additional time to consider comments and coordinate the regulation of ethylene oxide (EtO) from area sources with regulations for major sources.

U.S. EPA finalized additional GACT standards for non-EtO emissions including a pressure relief device (PRD) work practice standard, requirements for control device bypasses, and revisions to requirements for pressure vessels. Changes to requirements for equipment leaks, heat exchange systems, and process vents were also finalized as a result of U.S. EPA’s technology review. Several other changes are also covered at the end of this summary.

New GACT Standards Under CAA Section 112(d)(5)

U.S. EPA finalized the following new GACT standards pursuant to CAA Section 112(d)(5):

Source Type	Final Rule Requirements
PRDs	For PRDs not routed to a control device, process, fuel gas system, or drain system, facilities must: Install a monitoring system to alert when a PRD release occurs; Implement three redundant prevention measures; Conduct a root cause analysis and initiate appropriate corrective action in response to any PRD releases; and Limit the number of PRD releases to one or two releases in a three-year period depending on the cause of the release.
Bypass Lines	Any bypass of a control device is a deviation. Sources must continue to monitor for bypasses according to 40 CFR Part 63, Subpart SS, except that analyzer vents and high point bleeds are no longer exempted from the bypass provisions. Open-ended valves or lines that use a cap, blind flange, plug, or second valve and that meet certain requirements are not subject to bypass monitoring.
Pressure Vessels	Pressure vessels operated with a pressure greater than 204.9 kilopascals (kPa) and without emissions to atmosphere are no longer excluded from the definition of a storage vessel. U.S. EPA defined the term “pressure vessel.” For pressure vessels storing organic HAP with capacities of 20,000 gallons or more: Initial and annual leak monitoring is required, and a violation is defined as any reading above 500 parts per million (ppm). Valves and connectors that are unsafe to inspect/difficult to monitor are excluded from this requirement. The revised rule requires pressure vessels to operate as a closed system routed to control. PRD releases from pressure vessels are a violation of the standards.

Final Revisions Resulting from U.S. EPA’s CAA Section 112(d)(6) Technology Review

As indicated in the table below, U.S. EPA finalized technology review-based changes for equipment leaks, heat exchange systems, and process vents. None of the proposed changes for storage tanks, wastewater, flares, or fenceline monitoring were finalized.

Source Type	Final Rule Requirements
Equipment Leaks	Annual leak detection and repair (LDAR) for pumps in light liquid service, and valves and connectors in gas/vapor/light liquid service using Method 21 instrument monitoring (instead of audio, visual, or olfactory monitoring), including: 10,000 ppm by volume (ppmv) leak definition First attempt at repair in five days and repair by 15 days (although delay of repair is allowed in certain circumstances). Sources are required to comply with LDAR requirements in 40 CFR Part 63, Subpart H for the following: Closed vent systems and control devices; Compressors; Sampling connection systems; Open-ended valves or lines; Equipment in heavy liquid service; and Agitators in gas/vapor/light liquid service.
Heat Exchange Systems	U.S. EPA removed the leak monitoring exemptions for once-through heat exchange systems meeting certain National Pollutant Discharge Elimination System (NPDES) conditions. For heat exchange systems with a maximum cooling water flow rate of 8,000 gallons per minute or less: Monitoring must be conducted using the Modified El Paso Method with a leak definition of 6.2 ppmv. Quarterly monitoring preceded by an initial 6-month period where monitoring is conducted monthly. The delay of repair action level is 62 ppmv. If this value is exceeded, delay of repair cannot be used beyond 30 days. If 99 weight percent (wt.%) or more of the organic compounds that could leak are water soluble and have a Henry’s Law Constant < 5.0E-6 atm-m³/mol at 25°C, the system can be monitored using methods allowed in the previous rule [e.g., §63.104(b)].
Process Vents	Removal of the 50 ppmv metal HAP threshold in the definition of a “Metal HAP process vent.”

Other Changes

U.S. EPA finalized several other changes to the CMAS rule in addition to the technology review-based standards under CAA Section 112(d)(6). These include electronic reporting, removal of the affirmative defense provisions, repeat performance testing, and edits to address incorrect section references and minor editorial revisions.

For electronic reporting, facilities are required to submit compliance status reports, performance test reports, flare management plans, and periodic reports through U.S. EPA’s Central Data Exchange using the Compliance and Emissions Data Reporting Interface (CEDRI). Facilities are required to submit results of performance testing using the Electronic Reporting Tool (ERT) and semiannual compliance reports must be submitted using U.S. EPA developed reporting templates.

U.S. EPA removed the affirmative defense provisions consistent with a 2014 D.C. Circuit court case that vacated affirmative defense provisions for Portland cement kilns.

Facilities were previously allowed to use engineering assessments and design evaluations to demonstrate compliance with process vent and storage tank emissions limits; however, U.S. EPA removed that flexibility and instead is requiring sources to conduct performance tests of non-flare control devices at least once every five years to demonstrate compliance with emissions limits.

U.S. EPA also finalized several editorial changes and clarifications. The following is a list of notable revisions:

Removal of the provision at 40 CFR § 63.11498(b) that exempts facilities from complying with the wastewater control requirements in Table 6 of the rule during periods of startup and shutdown.
Addition of 40 CFR Part 60, Subparts VVa, VVb, IIIa, NNNa, and RRRa to the overlap provisions in 40 CFR § 63.11500(b).
Removal of the provisions that allow facilities to skip semiannual reporting for periods where certain events do not occur [40 CFR §63.11501(d)].

Compliance Dates

Facilities that were constructed or reconstructed on or before January 22, 2025 must comply with the new and revised requirements by April 1, 2029. Sources that commenced construction or reconstruction after January 22, 2025 are required to comply with all provisions by April 1, 2026, or upon startup, whichever is later.

Sources must begin submitting performance test results electronically starting June 1, 2026. Sources must start submitting Notification of Compliance Status (NOCS) reports electronically by August 31, 2026. Periodic reports must be submitted electronically starting on April 1, 2029 (or after the report template has been available in CEDRI for one year, whichever is later).

Wrap Up

The changes to the CMAS rule are just one of several U.S. EPA regulatory actions that impact the chemical industry that ALL4 is following closely. Depending on your facility’s specific configuration, the changes to the CMAS rule could result in substantive impacts to your monitoring, recordkeeping, reporting, and even day-to-day operations. Additionally, facilities that are area sources of HAP emissions may not have adequate environmental support staff and might need help understanding the impacts of the revised rule on their operations. If you need help understanding the revisions, identifying gaps, and implementing changes to comply with the new requirements, please reach out to your ALL4 Project Manager or Philip Crawford at pcrawford@all4inc.com.