Boiler MACT Amendments

On July 8, 2020, the EPA proposed to amend the 2013 NESHAP for Major Sources: Industrial, Commercial, and Institutional Boilers and Process Heaters, aka “Boiler MACT,” in response to three remands. The EPA is proposing 34 (of 90) emission limits for new and existing sources. Courts rule that the EPA must include all boilers subcaterogized using the 10% threshold for category-defining fuel type in the MACT floor analysis. Previously the EPA excluded units utilizing less than 90% from the MACT floor analysis. Of these 34 emission limits, 28 of the limits would become more stringent and six of the limits would become less stringent. EPA is also proposing that facilities would have up to 3 years after the effective date of the final rule to demonstrate compliance with these revised emission limits. In the second remand resulting from U.S. Sugar Corp. v. EPA, the Court ordered EPA to further explain its rationale in response to a public comment relating to the potential availability of alternative control technologies that reduce organic HAP without impacting CO emissions. EPA’s proposed response explains that none of the best performing units employ add-on alternative control devices for controlling organic HAP.

The devices regulated by the rule (boilers and process heaters) not only combust fuel for producing steam and/or process heat but serve a dual function in that they also effectively control organic HAP when good combustion conditions are present. For these reasons, the EPA concludes that the level of CO emissions, which indicates organic HAP reductions achieved through the use of combustion controls, is an appropriate surrogate for controlling organic HAP emissions from boilers and process heaters.

In the Sierra Club, et al. v. EPA remand, the Court found that EPA did not provide a sufficient explanation to support its rationale establishing a 130-parts per million (ppm) threshold as the lowest CO limit. In the 2013 rule, EPA determined, based on its data, that no additional reduction of organic HAP would occur once CO levels had been reduced to 130 ppm.

In the proposed response, EPA explains that its determination regarding the 130 ppm threshold is supported by an independent study and an EPA study that demonstrate a similar trend.

EPA will accept comment on the proposal for 60 days after publication in the Federal Register.

Go to and follow the online instructions for submitting comments.

Send comments by email to, Attention: Docket ID No. EPAHQ-OAR-2002-0058.