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EPA Finalizes Toughest Emission Standards to Date for Large Volatile Organic Liquid Storage Vessels
EPA finalized updates to the New Source Performance Standards for Volatile Liquid Storage Vessels (Including Petroleum Liquid Storage Vessels) in October 2024, and the new rule is already in effect. The new standards, codified at 40 C.F.R. Part 60, Subpart Kc (“Subpart Kc”), include a number of key differences from Subpart Kc’s predecessor rule, Subpart Kb. In terms of applicability, Subpart Kc has the potential to sweep in many more storage tanks than Subpart Kb, because Subpart Kc lowers the maximum true vapor pressure (TVP) applicability threshold from 2.2 psia for tanks between 20,000- and 40,000- gallons and 0.5 psia for 40,000-gallon or more tanks, to 0.25 psia for all 20,000-gallon or more tanks. If a tank exceeds the TVP applicability threshold, it will become subject to Subpart Kc if it was constructed, modified, or reconstructed after October 4, 2023. And while the meaning of construction and reconstruction is effectively the same as under Subpart Kb, EPA’s interpretation of what it means to “modify” a tank under Subpart Kc dispenses with the agency’s longstanding regulatory approach that a storage vessel cannot be “modified” merely by changing the type of liquid being stored without making any physical changes to the tank. Instead, under Subpart Kc, a tank is “modified” if the liquid being stored is changed to a volatile organic liquid (VOL) that has a maximum TVP that is higher than all the VOLs historically stored in or permitted for the tank. New Source Performance Standards do not typically refer to a source’s air permit as a basis for triggering applicability or otherwise.
In addition to lowering the applicability thresholds, Subpart Kc lowers the maximum TVP thresholds above which emission controls are required. Tanks between 20,000- and 40,000-gallons storing liquids with maximum TVP of 1.5 psia or more, and 40,000-gallon or more tanks storing liquids with maximum TVP of 0.5 psia or more, are required to install either a floating roof or a closed vent system that routes emissions to a control device. Under Subpart Kb, the maximum TVP thresholds above which storage vessels need to be equipped with controls are materially higher, i.e., less stringent. As context, the Subpart Kc 1.5 psia threshold for the largest tanks is even lower than the parallel provision applicable to refinery-specific tanks pursuant to the National Emission Standards for Hazardous Air Pollutants under 40 C.F.R. Part 63. Part 63 emission standards are often the most stringent for any particular source category, because they are intended to force the maximum emission reductions achievable through the application of control technology. Additional standards under Subpart Kc extend to tank rim seals and deck fittings, distillate flushing to reduce liquid volatility during roof landing or tank cleaning, and lower explosive limit monitoring, among others.
Subpart Kc took effect upon promulgation in October 2024, but it applies retroactively to storage vessels constructed, modified, or reconstructed after October 4, 2023. Industrial facility owners and operators should take a close look at the final regulation to determine how their tanks may be affected Subpart Kc, irrespective of the units’ regulatory status under Subpart Kb. Note, however, that because Subpart Kc was finalized with fewer than 60 days remaining in the 2024 Congressional session, the new Congress can void Subpart Kc in its entirety simply by approving a joint resolution of disapproval in accordance with the Congressional Review Act. As such, the implications of Subpart Kc could be short-lived.
