On October 15, 2024, the EPA finalized updates to its Volatile Organic Liquid (VOL) storage tank emission standards under 40 CFR 60 Subpart Kc. Subpart Kc applies to storage tanks with a capacity of 20,000 gallons or greater that are used to store VOL with a maximum true vapor pressure (TVP) of at least 0.25 psia [1] if they were constructed, reconstructed, or modified after October 4, 2023. Over the next five years, the proposed updates are expected to affect approximately 1,500 new and modified storage vessels within the following industries: Petroleum and Coal Products Manufacturing (NAICS Code 324000), Chemical Manufacturing (NAICS Code 325000) and Petroleum and Bulk Stations and Terminal (NAICS Code 422710).
The updates were proposed on October 4, 2023 (88 FR 68535) and require more stringent controls and design standards than Subpart Kb.
While the final rule is largely similar to the proposed version, three key updates are:
Thresholds for Emission Control Requirements: Subpart Kc requires a floating roof, or a Closed Vent System (CVS) to an emission control device, for tanks between 20,000 to 40,000 gallons storing liquids with maximum TVP of 1.5 psia or more, and tanks greater than 40,000 gallons with maximum TVP of 0.5 psia or more. This is a reduction in the maximum TVP requirements under the prior rule (40 CFR 60 Subpart Kb which still applies to VOL storage vessels constructed, reconstructed, or modified from July 24, 1984 to October 4, 2023), meaning tanks that would not have triggered control requirements under Subpart Kb may now require control measures. [2]
Rim Seal and Roof Fitting Requirements: Floating Roof tanks subject to Subpart Kc must comply with more stringent requirements on the types of rim seals and roof fittings that can be employed when compared to Subpart Kb floating roof requirements. Under Subpart Kc internal floating roof (IFR) and external floating roof (EFR) tanks are required to have a liquid-mounted or a mechanical shoe primary seal and a rim-mounted secondary seal. A seal system with a vapor-mounted primary seal will not satisfy Subpart Kc even if a secondary seal is used, except that modified tanks with an existing IFR may choose to comply with the Subpart Kb rim seal system requirements. In addition, IFR tanks will be required to undergo annual Lower Explosivity Limit (LEL) measurements in the space between the floating roof and fixed roof to assess seal performance.
Controlled Tank Degassing: Subpart Kc requires tank degassing events to be controlled for all fixed-roof tanks subject to the rule’s emission control requirements (i.e., using a CVS and control device to comply with the subpart) and all floating roof tanks with a capacity of 1 million gallons or greater storing a VOL with maximum TVP greater than 1.5 psia. In addition, control devices must now reduce inlet VOC concentrations by 98% versus the 95% control requirement under Subpart Kb.
Two significant ways that the final rule differs from the proposed version are:
Modification Definition: EPA has long held the position that a change in the type of material stored in a storage tank is not, by itself, a modification if the storage tank is capable of accommodating the new material. In the proposed Subpart, EPA changed their longstanding interpretation of modification, proposing that a change in the liquid stored in a storage tank to an organic liquid with a higher maximum true vapor pressure would be considered a change in the method of operation of the storage tank (i.e., would be considered to be a modification thus triggering NSPS Subpart Kc requirements). In the final rule, EPA revised their interpretation to clarify that a tank is only considered to have undergone a modification if it changes service “to store a VOL that has a greater maximum true vapor pressure than all VOL historically stored or permitted.” The reference to an emission unit’s air permit is a novel concept under 40 CFR Part 60 standards, however the updated language provides much needed clarification on tank “modification” and reduces the rule’s potential impact to the regulated industry.
Exemption for Very Low Maximum TVP: In the draft rule, any new, reconstructed, or modified VOL storage vessel that is 20,000 gallons or larger would have been subject to the rule. While the control requirements would only have applied to larger tanks storing a VOL with a maximum TVP greater than 0.5 psia, tanks storing heavy VOLs such as distillate fuel would have been subject to various recordkeeping requirements. The final rule exempts tanks storing VOLs with a maximum TVP less than 0.25 psia, thereby reducing the regulatory burden for industry.
If you have any questions regarding the revisions or need assistance with the implications for your facility, contact your local CEC office.
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[1] 1 psia ~ 6.895 kPa and 1,000 gallons ~ 3.785 cubic meters. Although Subpart Kb as well as the proposed Subpart Kc used metric units primarily, the final Subpart Kc uses imperial units as the primary values so we have used that convention here.
[2] Subpart Kb does not apply to storage vessels with a capacity greater than or equal to ~40,000 gallons storing a liquid with a maximum true vapor pressure less than ~0.51 psia or with a capacity greater than or equal to ~20,000 gallons but less than ~40,000 gallons storing a liquid with a maximum true vapor pressure less than ~2.18 psia.
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