See the latest EHS federal and state regulatory updates due to COVID-19


On July 8, EPA Administrator Andrew R. Wheeler signed proposed amendments to 40 CFR 63 Subpart DDDDD (the Boiler MACT). These amendments are being proposed in response to a U.S. Court of Appeals for the District of Columbia Circuit (D.C. Circuit) decision in July 2016 which remanded several numeric emission standards to EPA and required EPA to address other issues. A December 2016 motion by EPA was granted by the court to remand the emission standards back to EPA without vacatur. This proposed rule is of high importance to facilities which operate boilers subject to emission standards under the Boiler MACT.

The Boiler MACT regulates emissions of Hazardous Air Pollutants (HAP) from industrial, commercial, and institutional boiler and process heaters located at major sources of HAP. No emissions standards under the rule apply to natural gas (gas 1) units; however, for several categories of boilers including solid and liquid fuel units, the rule establishes emissions standards for particulate matter (PM) with total selected metals (TSM) as an alternative to the PM standard, carbon monoxide (CO), hydrogen chloride (HCl), and mercury (Hg). The emissions standards differ based upon on the subcategories that apply to a boiler under the rule. When EPA establishes Maximum Achievable Control Technology (MACT) emission standards, a MACT floor analysis of emissions data is completed to establish standards based on data from top performing units. The D.C. Circuit ruled that EPA inappropriately excluded certain units from the MACT Floor analysis and remanded the emissions standards back to EPA.

Through this action, EPA is proposing to amend 34 emission standards for several categories of boilers as summarized in these tables. Twenty-eight limits would become more stringent, while six would become less stringent. EPA is proposing that facilities would have three years from the effective date of the final rule to demonstrate compliance with the revised emission standards. Please note, while changes are being proposed to the CO emission standards, no changes are being proposed to CO limits for boilers that demonstrate compliance on a 30-day rolling average basis using a CO continuous emissions monitoring system (CEMS).

The D.C. Circuit also remanded to EPA the use of CO as a surrogate for organic HAP for further explanation. Specifically, the court requested EPA provide information of the availability of potential control devices that reduce organic HAP without impacting CO emissions. In a separate case in March 2018, the court also remanded EPA's decision to establish a 130 parts per million (ppm) CO standard for certain subcategories for further explanation. In 2013, EPA determined that no additional reduction of organic HAP would occur at CO levels less than 130 ppm. The proposed rule provides additional explanation of these issues.

As part of this action, EPA is also proposing several technical corrections, including:

  • A grammatical change to 40 CFR 63.7500(a)
  • Removal of the requirement to collect samples during the test period at 1-hour intervals in 40 CFR 63.7521(c)(1)(ii)
  • Clarification that the establishment of a pH operating limit is not required for a PM wet scrubber in 40 CFR 63.7530(b)(4)(iii) [Note that a pH operating limit is still required for wet acid gas scrubbers]
  • Clarification that certification requirements only apply to PM CEMS and not to PM continuous parameter monitoring systems (PM CPMS) in 40 CFR 63.7540(a)(9), as no performance specification exists for PM CPMS
  • Technical correction of the definition of “Other Gas 1 Fuel” in 40 CFR 63.7575 to clarify that the maximum concentration is “40 micrograms per cubic meter of gas” rather than “40 micrograms per cubic meter of mercury”
  • Addition of the definition of “12-month Rolling Average” in 40 CFR 63.7575
  • Technical correction of the definition of “Steam Output” in 40 CFR 63.7575 to refer to “steam headers” instead of “steam heaters”
  • Revision of the alternative PM emission standard for new stoker/sloped grate/others designed to burn kiln-dried biomass fuel in Table 1 to Subpart DDDDD from 4.2E-01 lb/MMBtu to 4.3E-01 lb/MMBtu to correct a rounding error
  • Revision of footnote “b” in Table 7 to Subpart DDDDD to state that when multiple performance tests are conducted, the maximum operating load should be selected as the lower of the maximum values established during performance testing
  • Revision of the equation reference in Table 8 to Subpart DDDDD for boilers that comply with emission limits using fuel analysis

Suggested Actions

Although the rule and amended emissions standards are not finalized, Trinity recommends the following action items for facilities subject to Boiler MACT emissions standards:

  • Determine whether your boiler is in a subcategory with emissions standards that will be modified as a result of the proposed rule
  • Assess available emissions data from prior performance tests/fuel analysis against the proposed limits
  • Evaluate how the changes will impact your facilities overall compliance strategy and/or operating limits

Trinity has assisted numerous facilities across the country with developing Boiler MACT compliance strategies as well as preparing monitoring plans, fuel analysis plans, notification of compliance status (NOCS) reports and compliance reports (including electronic reporting in EPA's CDX-CEDRI system). Please contact your local Trinity office if you have any questions or would like assistance in evaluating the impact of the proposed amendments to your facility.