Blog   |   Apr 10th, 2018 Court Tells EPA to Review “Arbitrary” Emissions Standard for Industrial Boilers

Trc Boiler Mact Rule

The District of Columbia Court of Appeals has ordered the Environmental Protection Agency to reconsider emission limits for industrial, commercial and institutional boilers, calling levels that were put into place for several heater/boiler subcategories in 2013 “arbitrary and capricious.”  

In the meantime, however, those levels will remain in effect until the EPA finishes its next rulemaking.


On March 16 the DC Court of Appeals issued a decision on two separate challenges to the EPA’s emissions regulations for industrial, commercial and institutional boilers and process heaters, commonly known as Boiler MACT. 

The first challenge concerned emission limits in the rule for carbon monoxide (CO), which had been used by EPA in the Boiler MACT rulemaking as a proxy for non-dioxin organic Hazardous Air Pollutants (HAP).  The second challenge addressed how boilers are to be operated during startup and shutdown.

The court upheld the startup and shutdown provisions of the rule, determining that the EPA’s justifications for the startup and shutdown provisions were technically sound.  As such, this portion of the current Boiler MACT rule will remain unchanged from the version finalized in November 2015.

The court did, however, reject EPA’s justification for setting the floor for CO emissions within the rule at 130 ppm, and remanded EPA to “reconsider its decision to adopt the 130 ppm CO limits.” 

Establishment of the 130 ppm Standard

As part of the 2011 rulemaking, EPA determined that CO was a suitable surrogate for non-dioxin organic HAP (which was reaffirmed by the court in the March 16 decision). The reasoning behind this being that “organic HAP are products of incomplete combustion” and “CO is a good indicator of incomplete combustion.”  As such, “minimizing CO emissions will result in minimizing non-dioxin organic HAP.”  Using the data it had for industrial boiler CO emissions, it set a MACT floor for CO as it would normally do for HAP. 

While initially establishing MACT floors lower than 130 ppm, EPA revised them upward during the 2013 reconsideration of the rule.  As justification for this decision, EPA cited the fact that the correlation between lower CO emission and lower HAP emissions wasn’t as strong with lower levels of CO (less than 150 ppm).  The logic at the time was that since no further reduction of HAP could be shown with reduction of CO below 130 ppm, then that was the lowest the emission levels needed to be set.

The DC Circuit found this determination to be “arbitrary and capricious” and said the EPA’s “only support for its upward-revised floors was the very data it had just dismissed as inaccurate.” It ordered the EPA to reconsider the standards and whether its decision to raise the MACT floor can be adequately supported by data.  EPA must consider whether the standards it adopts in response to this remand are compliant with Section 7412 of the Clean Air Act and if beyond-the-floor standards will apply. 

What It Means

As the current standard has not been vacated, the relevant boiler subcategories to which the 130 ppm standard applies – units that combust coal, heavy liquid fuels or “gas 2” fuels – will require continued compliance with this limit.  Whether the standard will change depends on how well EPA can justify the current levels of the CO standard with regard to its correlation with maximal reduction of HAP emissions.

One thing to keep in mind is that the court agreed with EPA that when the agency is using a surrogate such as CO, the MACT floor for the surrogate should be set such that the lowest achievable levels of HAP are attained, not necessarily the lowest achievable levels of the surrogate.  This means that, in reconsidering the standard, it must be shown that below the level at which the floor is set, no further reduction in HAP can be achieved. 

We shall see in the coming months whether the EPA can more precisely pinpoint that level and whether the emission standards for the relevant subcategories will change. In the meantime, TRC will continue to monitor the situation and can help facilities assess the potential impact of lowered CO standards on their operations. 

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Blog Authors

Neel Kotra

Neel Kotra, EIT, is a combustion and air quality compliance engineer in TRC’s Atlanta office. He has worked with clients in a wide variety of industries on Boiler MACT compliance, both from a combustion efficiency/tune-up standpoint and on regulatory compliance. He has an MS in Environmental Engineering from Georgia Tech.

John Bacon

John Bacon

John A. Bacon, MBA, LPG, CEM, is a combustion and energy optimization specialist in TRC’s Milwaukee office. He has more than 24 years of experience in the fields of health, safety, and environmental regulatory compliance. John manages TRC’s combustion services, sales and marketing and is a published author relating to combustion optimization, energy efficiency, and the Boiler MACT Rule.