EPA Reclassifies Major Sources as Area Sources Under Section 112 of the Clean Air Act

On January 25, 2018, the U.S. Environmental Protection Agency (EPA) issued a guidance memorandum withdrawing the “once in always in” policy for the classification of major sources of hazardous air pollutants under section 112 of the Clean Air Act.  Sources of hazardous air pollutants previously classified as “major sources” may now be reclassified as “area” sources when the facility limits its potential to emit below major source thresholds.


The Clean Air Act defines a “major source” as a one that emits, or has the potential to emit, 10 tons per year of any hazardous air pollutant, or 25 tons per year or more of any combination of hazardous air pollutants.  Sources with emissions below this threshold are classified as “area sources.” Different control standards apply to the source depending on whether or not it is classified as a “major source” or an “area source.”


In 1995, EPA established a “once in always in” policy that determined that any facility subject to major source standards would always remain subject to those standards. Now, EPA has determined that it had no statutory authority under the Clean Air Act to place a time limit on when a facility may be determined to be an area source.


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Carlos E. Colón Franceschi







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