In a major change in air permitting policy, on January 25, 2018 U.S. EPA reversed its longstanding "once in, always in" policy governing what sources are subject to major source regulations for the emissions of air toxics under Section 112 of the Clean Air Act. Under a 1995 policy memorandum issued by the agency, sources that had the potential to emit above the major source thresholds at the time a standard applied to a particular source category were "always in," and had to forever comply with that standard—even if the source subsequently installed emission control equipment or switched to non-hazardous air pollutant substances, and took enforceable limits to keep emissions below those limits. The January 25 memorandum reverses that policy, and authorizes the reclassification of a major source to an area source at such time as the source takes enforceable limits on potential to emit below the major source thresholds.

This change will likely lead to numerous sources seeking reclassification from "major" to "area" source status, in order to take advantage of more streamlined recordkeeping and reporting requirements applicable to such facilities. It may also have implications for some enforcement cases currently being pursued by the agency. States have incorporated the federal major source requirements into air permits, and as such, the requirements remain in effect until the permit is modified. Facilities should review their air permits and work with state agencies to remove the unnecessary and burdensome requirements.

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