This guidance is based on a plain-language reading of the statute that is in line with EPA’s guidance for other provisions of the Clean Air Act. It will reduce regulatory burden for industries and the states, while continuing to ensure stringent and effective controls on hazardous air pollutants.

—Bill Wehrum, assistant administrator of EPA’s Office of Air and Radiation

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 a 1995 memo, 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, even if production processes changed or controls were implemented that eliminated or permanently reduced that facility’s potential to emit hazardous air pollutants.

The new memo finds that EPA 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, and that a plain language reading of the Act must allow facilities to be reclassified as area sources once their potential to emit hazardous air pollutants falls below the levels that define major sources.

EPA anticipates that it will soon publish a Federal Register notice to take comment on adding regulatory text that will reflect EPA’s plain-language reading of the statute as discussed in this memorandum.