U.S. EPA Has Revised its Standards for New and Modified Volatile Organic Liquid Storage Tanks

On October 15, 2024, the U.S. Environmental Protection Agency (U.S. EPA) published final amendments to the Standards of Performance for New Stationary Sources, or New Source Performance Standards (NSPS), for Volatile Organic Liquid (VOL) Storage Vessels (Including Petroleum Liquid Storage Vessels) for Which Construction, Reconstruction, or Modification Commenced After July 23, 1984, and On or Before October 4, 2023 (NSPS Subpart Kb). U.S. EPA also finalized a new NSPS Subpart Kc for VOL Storage Vessels (Including Petroleum Liquid Storage Vessels) for Which Construction, Reconstruction, or Modification Commenced After October 4, 2023. This article summarizes the changes to NSPS Subpart Kb and the new requirements in NSPS Subpart Kc. Note that applicability of the new Subpart Kc is determined differently than facilities historically determined applicability of Subpart Kb.

Changes to NSPS Subpart Kb

U.S. EPA promulgated two changes to NSPS Subpart Kb. The first change, which coincides with the finalization of the new Subpart Kc, adds a “cut-off” to the applicability dates. Subpart Kb now applies to those VOL storage vessels that commenced construction, reconstruction, or modification after July 23, 1984, and on or before October 4, 2023. The second change to Subpart Kb is the addition of electronic reporting requirements. Starting on October 15, 2024, reports required by Subpart Kb must be submitted electronically through U.S. EPA’s Compliance and Emissions Data Reporting Interface (CEDRI) in portable document format (PDF).

New NSPS Subpart Kc

As previously stated, Subpart Kc applies to VOL storage vessels that commenced construction, reconstruction, or modification after October 4, 2023 (the date the new standards were proposed). While Subpart Kc is similar to Subpart Kb, there are significant differences that tank owners and operators should know about. These differences are found in most aspects of the rule (e.g., applicability, controls, monitoring, etc.) and are highlighted below.

Applicability

U.S. EPA has lowered (as compared to Subpart Kb) both the general rule applicability and control thresholds that are based on the maximum true vapor pressure (MTVP) of the stored VOL. Subpart Kc applies to each storage vessel with a capacity of 20,000 gallons or more storing a VOL with a MTVP of 0.25 pound per square inch absolute (psia) or more. For comparison, Subpart Kb applies to storage vessels with a capacity of 20,000 gallons or more storing a VOL with a MTVP of 2.2 psia or more, and storage vessels with a capacity of 40,000 gallons or more storing a VOL with a MTVP of 0.5 psia or more.

Controls are required under Subpart Kc for vessels with a capacity of at least 20,000 gallons that store a VOL with a MTVP of 1.5 psia or greater, and for storage vessels with a capacity of at least 40,000 gallons that store a VOL with a MTVP of 0.5 psia or greater. These MTVP control thresholds are significantly lower than the values in Subpart Kb (4.0 psia for 20,000-40,000 gallon vessels, and 0.75 psia for vessels of 40,000 gallons or more).

In one of the biggest changes from Subpart Kb to Kc, U.S. EPA also revised their interpretation of modification as it applies to storage vessels under Subpart Kc. Previously, U.S. EPA did not consider a change in service to a VOL with a higher MTVP a modification unless the change required a physical modification of the storage vessel, but in Subpart Kc, U.S. EPA considers storing a VOL that has a higher MTVP than all VOL historically stored or permitted a modification, regardless of whether a physical change is required. Furthermore, the exemption in 40 CFR §60.14(e)(4) regarding alternative fuel or raw material does not apply under Subpart Kc. This is a significant change in how applicability is determined.

Air Emissions Control Requirements

For vessels storing a VOL with a MTVP less than 11.1 psia, Subpart Kc includes three compliance options:

• Use a fixed roof in conjunction with an internal floating roof (IFR) equipped with a liquid-mounted or mechanical shoe primary seal and a continuous rim-mounted secondary seal, either a flexible fabric sleeve or gasketed sliding cover on pipe columns (if any), specific 2000 U.S. EPA Storage Tank Emission Reduction Partnership Program (STERPP) compliant guidepole configurations, and gasketed covers;
• Use an external floating roof (EFR) equipped with a liquid-mounted or mechanical shoe primary seal and a continuous rim-mounted secondary seal, with welded deck seams and both seals meeting certain gap requirements, specific guidepole configurations, and gasketed covers; or
• Use a closed vent system (CVS) routed to a control device that achieves 98 percent control efficiency, a fuel gas system, or a process.

For vessels storing a VOL with a MTVP of 11.1 psia or more, Subpart Kc requires a CVS routed to a 98% effective control device, fuel gas system, or process. Subpart Kc contains additional requirements to those in Subpart Kb for any vessels where emissions are routed to a CVS and controls. The vacuum pressure at which vacuum breaking devices must close is -0.1 inches of water (-0.0036 pounds per square inch gauge, psig). Vessels must be designed to operate at elevated pressures (1 psig above MTVP plus any back pressure from the control device) without venting to the atmosphere, or the vapor recovery system must be designed and operated to prevent venting from the storage vessel. If storage vessels are designed to operate at elevated pressures, the control device may be taken out of service for maintenance provided that the storage vessels are operated with no emissions to the atmosphere. Monitoring systems must be installed to detect pressure releases from each pressure relief device (PRD) or vacuum breaking device on a storage vessel and each PRD on the closed vent system. Open-ended valves or lines that use a cap, blind flange, plug, or second valve are not considered to be bypass lines.

These standards apply at all times; there is no compliance exemption or alternate standard for periods of startup, shutdown, or malfunction.

Degassing Requirements

New for Subpart Kc, the rule  includes degassing standards for storage vessels equipped with a CVS routed to a control device, fuel gas system, or process, and for IFR and EFR storage vessels that have a capacity of 1 million gallons or more storing a VOL with an MTVP of 1.5 psia or more. When degassing a storage vessel that requires control, facilities must remove liquids as much as possible and control vapors until the vapor space concentration is less than 10% of the lower explosive limit (LEL), or for nonflammable liquids, 5,000 parts per million by volume (ppmv) as methane.

Testing, Monitoring, and Inspection Requirements

Subpart Kc significantly expands upon the testing, monitoring, and inspection requirements included in Subpart Kb. Some of the major testing, monitoring, and inspection requirements in Subpart Kc are:

• Visual or audible alarm systems to monitor when floating roofs approach landing heights and when roofs have landed.
• Quarterly audible, visual, and olfactory (AVO) inspections of closed vent systems (leaks detected using AVO methods are leaks triggering corrective action) and annual Method 21 instrument monitoring.
• Annual monitoring of the vapor space between an IFR and fixed roof to demonstrate that the vapor space concentration is at or below 25% of the LEL. This is a new requirement for Subpart Kc and U.S. EPA acknowledges in the rule language that additional controls beyond those required by the rule might be necessary to achieve compliance.
• Internal inspections of IFRs at least once every 120 calendar months (can be conducted while the vessel is in service) or each time the vessel is emptied and degassed.
• Inspection of EFR fittings during annual seal gap measurement inspections to ensure covers are closed and gasketed with no visible gaps and no tears in sleeves, wipers, or similar controls used for a given fitting.
• For vessels with emissions routed through a CVS to control, monitoring systems must be installed to detect pressure releases from each PRD, conservation vent, or vacuum breaking device on a storage vessel and each PRD on the closed vent system. Additionally, facilities must report when a vacuum breaking device failed to close prior to the storage vessel reaching atmospheric pressure.
• Performance tests on non-flare control devices initially (i.e., within 180 days of becoming subject to the rule) and at least once every 60 months thereafter. Facilities must also use continuous monitoring systems (CMS) to monitor control device operating parameters to continuously demonstrate compliance.
• The MTVP of the VOL must be determined prior to initial filling or refilling the storage vessel with a new VOL. The MTVP can be determined from reference data and physical testing is not required, except for vessels storing a mixture of indeterminate composition or a mixture of unknown variable composition.
• For vessels storing a mixture of indeterminate composition or a mixture of unknown variable composition, physical testing of the MTVP is required initially and once every six months. If testing demonstrates that the storage vessel meets the control requirement applicability thresholds, the vessel must be emptied and taken out of service until appropriate controls are installed.

Recordkeeping and Reporting

Subpart Kc includes various detailed recordkeeping requirements. U.S. EPA finalized a requirement that all notifications and reports must be submitted electronically using CEDRI (semiannual reports are required in CEDRI after the template has been available for one year). Semiannual reports will cover the periods of January 1 to June 30 and July 1 to December 31. These reports must be submitted by August 31 and February 28 or 29, or according to submittal dates in your Part 70 or 71 operating permit.

Conclusion

As described above, Subpart Kc contains several new requirements in comparison to Subpart Kb. Facilities that operate VOL storage vessels should carefully review the new requirements to understand how the changes may impact operation of their storage vessels. Facilities should also begin documenting their VOL storage vessels’ service history to identify future changes in service that might constitute a modification. If you have specific questions on the recent rule changes or need help implementing the new requirements at your facility, please contact me at pcrawford@all4inc.com, or your ALL4 project manager. We encourage you to also check our Chemical Industry Resources page for blogs, webinars, workshops, and other resources with information on changes impacting the chemical industry.