U.S. EPA has Finalized Updates to the Mercury and Air Toxics Standards for Power Plants

On April 24, 2024, the U.S. Environmental Protection Agency (U.S. EPA) signed final revisions to the National Emission Standards for Hazardous Air Pollutants (NESHAP) for Coal- and Oil-Fired Electric Utility Steam Generating Units (EGUs), also known as the Mercury and Air Toxics Standards (MATS). MATS includes standards to limit emissions of mercury, acid gas hazardous air pollutants (HAPs), non-mercury HAP metals, and organic HAPs from coal- and oil-fired EGUs. An EGU is a fossil fuel-fired combustion unit of more than 25 megawatts (MW) that serves a generator that produces electricity for sale. A unit that cogenerates steam and electricity and supplies more than one-third of its potential electric output capacity and more than 25 MW electric output to any utility power distribution system for sale is also considered an EGU. These MATS revisions are a result of U.S. EPA’s review of the 2020 risk and technology review (RTR) conducted under the previous administration.

What’s New?

The revised standards include more stringent requirements to reduce mercury and filterable particulate matter (fPM) emissions from EGUs and represent a significant update to the original 2012 MATS. These more stringent standards are based on U.S. EPA’s revised technology review and its determination that technologies and/or methods of operation are currently available to achieve additional HAP control from coal-fired EGUs at reasonable costs. No revisions were made to the 2020 risk review, which showed that risks from the source category are acceptable and the NESHAP provides an ample margin of safety to protect public health.

The MATS updates include a significant reduction in the emissions limits for existing coal-fired EGUs. The lower fPM limit is based on a review of the actual emissions from coal-fired EGUs that indicated a majority of sources were reporting fPM emissions significantly below the current limit and achieving these emissions rates at lower costs than originally estimated. U.S. EPA has lowered the emissions standard for fPM from 0.030 to 0.010 pounds per million British thermal units (lb/MMBtu). This level of the fPM standard is believed to be the lowest level compatible with the use of particulate matter (PM) continuous emissions monitoring systems (CEMS). As part of this change, U.S. EPA is eliminating the low-emitting EGU (LEE) compliance option for fPM/non-mercury metals, so all coal- and oil-fired EGUs will have to demonstrate compliance with the fPM limit using PM CEMS and report the data to the online Emissions Collection and Monitoring Plan System (ECMPS). Although U.S. EPA had proposed to eliminate the option to comply with the HAP metals standard, this change was not finalized, and instead, the alternate emissions limits for the individual non-Hg HAP metals were reduced proportional to the reduction in the fPM limit. EGU owners can still choose to comply with either the non-Hg HAP metals limits or the fPM limit, but must request and receive approval of a non-Hg HAP metal continuous monitoring system as an alternate test method if they choose not to comply with the fPM limit.

U.S. EPA has also lowered the mercury emissions limit for existing lignite-fired EGUs from 4.0 to 1.2 pounds per trillion British thermal units (lb/TBtu), a level that is aligned with the mercury standard that other coal-fired power plants must achieve under the MATS. The new standards will take effect three years after the effective date of the final rule (60 days from publication in the Federal Register).

In addition, in response to a reconsideration petition from environmental organizations, U.S. EPA has revised the startup requirements in MATS by removing the second option for defining the startup period. EGUs must be in compliance with the numeric emissions standards at the conclusion of startup. Under the remaining startup definition, startup ends when any steam from the boiler is used to generate electricity. Under the now-eliminated second startup definition, startup ended four hours after electricity was generated. According to U.S. EPA, the majority of EGUs were utilizing the first definition and could implement their necessary HAP controls prior to generating electricity. The new startup requirements take effect 180 days from the effective date of the final rule, as U.S. EPA believes there are only a few EGUs affected by this change, the change is achievable, and the change will require little to no expenditures.

Now what?

This is just one of four new rules that were recently signed that will affect fossil fuel-fired power plants, and ALL4 is tracking them. The MATS rule revisions will become effective 60 days following publication in the Federal Register and the compliance clock for the new requirements will begin. ALL4 can assist you with understanding the new requirements, in evaluating the impact of the rule on your facility, and with developing a strategy to comply with the revised requirements (including implementing PM CEMS). If you have questions about how the proposed MATS revisions could affect your facility’s program, or what your next steps should be, please reach out to your ALL4 project manager or to me at amarshall@all4inc.com. ALL4 is monitoring all updates published by the U.S. EPA on this topic, and we are here to answer your questions and assist your facility with any aspects of MATS compliance.