In January 2018, EPA issued a guidance memorandum that withdrew the long-standing “once in always in” policy for the classification of major sources of hazardous air pollutants under section 112 of the Clean Air Act, the National Emission Standards for Hazardous Air Pollutants or NESHAPs. A major source of HAPs is a stationary source that has the potential to emit 10 tons per year or more of any HAP or 25 tons per year or more of a combination of HAPs. An area source is a stationary source that does not emit HAPs above these thresholds. EPA’s previous guidance under the Seitz Memo, in place since 1995, stated that once a source became a major source of hazardous air pollutants (HAPs), they could not be reclassified as an area source even if potential HAP emissions drop below major source thresholds. Once they were “in” as a major source, that facility would always be in. The new policy allows these sources previously classified as major sources to be reclassified as area sources when the facility limits the potential to emit HAPs below the major source thresholds.
EPA’s Federal Register notice about the guidance states that EPA will publish a follow-up Federal Register document to take comment on adding regulatory text to reflect this guidance.