The EPA published a final rule on September 14, 2016 to once again revise its maximum achievable control technology (MACT) standard for boilers. In this latest revision, EPA responded to various requests for reconsideration of its "area source" boilers rule, the rule that applies only to boilers located at relatively minor emission sources. The most significant revision in this latest rulemaking involves changes to the definitions of "startup" and "shutdown" to mirror the similar revisions made in EPA's other MACT rules. That is, the area source boiler rule will now define startup in two different ways, one of which allows a 4 hour window during which only work practice standards will apply in lieu of the otherwise applicable numeric emission limits. EPA also eliminated the affirmative defense provision for unavoidable malfunctions, which, until 2014, was the central component of EPA's policy for addressing emissions resulting from malfunctions. However, in light of a recent D.C. Circuit decision rejecting the malfunction affirmative defense in another MACT standard, EPA has begun removing those provisions from its rules, so the decision to eliminate it from the area source boiler MACT is no surprise. The lack of an affirmative defense or any other provision to address malfunctions will now leave boiler owners vulnerable to penalties for emission exceedances even if due to unforeseeable and unpreventable malfunctions. As important as what the agency revised, however, is what the agency did not revise—most notably its decision to maintain a separate subcategory for "limited use units" subject only to a 5-year tune-up requirement. In its proposed rule, EPA had sought comment on whether that subcategory should be eliminated, raising the concern among industry representatives that EPA could decide to regulate limited use units—those that only operate for less than 10 percent of their annual capacity—just like units that operate far more often. In comments, industry representatives supported the limited use subcategory for a variety of reasons, including the fact that limited use units would still be required to tune-up after less total operating time compared to other units, and the agency agreed. The text of the final rule may be found here.
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