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In First Update Since ’87, EPA Proposes New Source Performance Standards for Volatile Organic Liquid

On October 4, 2023, the U.S. Environmental Protection Agency (EPA) proposed New Source Performance Standards (NSPS) Subpart Kc in the Federal Register. Once finalized, the regulations will affect volatile organic liquid (VOL), including petroleum storage vessels constructed, modified, or reconstructed after the October 4, 2023, proposal date.

The EPA is also proposing changes to NSPS Subpart Kb regarding reporting requirements. As the EPA has done for other recent proposed rulemakings, the proposed rule language does not appear in the Federal Register publication; the proposed Subpart Kc language is found here and the proposed Subpart Kb revisions are found here. Comments on the proposed rules are due to the EPA by November 20, 2023.

What changes are proposed in NSPS Subpart Kc?

Proposed NSPS Subpart Kc changes include:

  • An affected facility is any storage vessel that is constructed, modified, or reconstructed after October 4, 2023, that has a capacity of 20,000 gallons (476.3 barrels) or more and stores VOLs.
  • No change: Prior exemptions, including pressure vessels designed to operate over 29.7 pounds per square inch absolute (psia) and petroleum/condensate vessels with capacities under 420,000 gallons (10,000 barrels) prior to custody transfer, remain applicable.

Updated vapor pressure thresholds requiring controls:

  • Storage vessels with capacities between 20,000 gallons and 40,000 gallons (952.4 barrels) must use controls when storing VOLs with a maximum true vapor pressure (TVP) of 1.5 psia or greater.
  • Storage vessels with capacities of 40,000 gallons or more must use controls when storing VOLs with a maximum TVP of 0.5 psia or greater.

Updates for VOL vessels storing liquids with maximum TVP under 11.1 psia:

  • Internal floating roof (IFR) vessels are designated as the “Best System of Emission Reduction” (BSER) and must achieve 98 percent control efficiency (an increase from 95 percent in Subpart Kb).
    • The primary seal must be liquid-mounted or a mechanical shoe and must have a rim-mounted secondary seal; gauge hatches and sample ports must be gasketed; and guidepoles must meet the provisions in the 2000 EPA Storage Tank Emissions Reduction Partnership Program (STERPP).
    • Alternative compliance approaches achieving 98 percent control by using either an external floating roof (EFR) or closed vent system (CVS) and a control device are allowed.
      • EFRs must have a liquid-mounted or mechanical shoe primary seal, be equipped with a rim-mounted secondary seal, and be constructed with welded deck seams. If the guidepole is unslotted, using a gasketed sliding cover and pole wiper is allowed. If the guidepole is slotted, only a liquid-mounted primary seal is allowed, and the slotted guidepole must be equipped with a sliding cover, pole sleeve, and pole wiper (with or without a float).
      • Fixed roof storage vessels with control devices are allowed as long as an overall 98 percent reduction in volatile organic compounds (VOC) emissions is achieved.

Updates for VOL storage vessels storing liquids with maximum TVP equal to or greater than 11.1 psia:

  • A closed vent system with a control device meeting 98 percent control efficiency is required, and, if the control device is a flare, it must meet the MACT Subpart CC 63.670 requirements, including the minimum net heating value requirements in 63.670(j)(6).
  • Storage vessels must have a design operating range no less than 1 psi greater than the maximum TVP of the liquid stored, including addressing any backpressure that may occur when the vessel is being filled at its maximum rate. Also, vacuum breakers must have a closing pressure of no less than 0.1 pounds per square inch in gauge (psig) vacuum.

A change to what constitutes a “modification” for storage vessels:

  • In a move that changes past precedent, the EPA proposes that a change in VOL to a liquid with a higher maximum TVP is not a “use of an alternative fuel or raw material,” and instead will be considered a “change in the method of operation” of a storage vessel, thus is considered a modification under Subpart Kc.
  • Modified storage vessels equipped with an IFR or an EFR storing VOLs less than 11.1 psia only have to meet applicable NSPS Subpart Kb control requirements and will not otherwise have to upgrade the rim seals. However, modified storage vessels equipped with a closed vent system to a control device will have to make necessary changes to achieve a 98 percent control efficiency.

Updates for storage vessel degassing emission controls:

Emission controls are proposed when degassing a storage vessel with a capacity of 1,000,000 gallons (23,810 barrels) or more storing VOLs with a maximum TVP of 1.5 psia or more. The control device must achieve 98 percent destruction efficiency until the lower explosive limit (LEL) reading in the vessel headspace is less than 10 percent LEL.

Updates to storage vessel inspection requirements:

  • Required annual visual and LEL inspections of IFR storage vessels, with repairs required (including potential IFR replacement) if the LEL reading is greater than 25 percent. Repairs must be performed within 45 days, with a possible 30-day extension.
    • LEL monitoring (detailed monitoring procedures; similar to the proposed Gasoline Distribution MACT Subparts R and 6B regulations) based on results from 5-minute rolling average readings taken over 20 minutes, with the LEL reading taken not more than 3 feet above the roof deck with windspeeds at the top of the storage vessel 5 miles per hour (mph) or less if practicable. No LEL readings are allowed if the windspeed is greater than 15 mph or exceeds the location’s annual average wind speed, whichever is less.
    • No change: IFR storage vessels maintain the requirement for thorough visual (i.e., top side and bottom side) inspection for fittings, gaskets, seals, etc. every 120 months (note the units are in months, not years as in NSPS Subpart Kb).
  • EFR storage vessel seal inspections remain generally the same as current NSPS Subpart Kb requirements.
  • Visual or audible alarm warnings when the IFR or EFR roof approaches specified landing heights are required.
  • For closed vent systems, quarterly audible, visual, or olfactory (AVO) monitoring and annual Method 21 instrument monitoring (500 ppmv limit) are required.
    • Closed vent system bypasses must be monitored with either a flow indicator with continuous monitoring (at least every 15 minutes) or must be equipped with a bypass valve that has a car seal-type lock.
    • Each pressure relief device (PRD) on the vessel or closed vent system must be equipped with monitoring that identifies the release, records the time and duration of the release, and notifies operators immediately of the release. PRDs that only route to the control device, back to process, to a fuel gas system, or to a drain system do not require monitoring.

Updates to control device monitoring:

  • Install, calibrate, maintain, and operate a backpressure regulator valve calibrated to open at the minimum pressure set point corresponding to the minimum inlet gas flow rate, with annual verification of proper setting and operation.
  • Non-flare control devices:
    • Initial performance testing within 180 days, as well as performance testing within 60 months following the previous performance test.
    • The performance tests will establish a 3-hour rolling average enforceable operating limit for the control device, generally based on continuously monitored temperature (see proposal for details).
  • Flare control devices
    • Flares must be monitored consistent with the MACT Subpart CC flare requirements in 63.671.
    • Continuous monitoring systems must be installed, calibrated, operated, and maintained in accordance with an established system monitoring plan.

Updates to startup, shutdown, and malfunction (SSM):

Consistent with other rulemakings, compliance with the requirements will be continuous. No exemptions will be allowed for SSM events. The EPA proposes to override a current exemption in 40 CFR 60.11(c) that exempts opacity from SSM events.

Updates to electronic reporting in NSPS Subparts Kb and Kc:

  • Electronic reporting requirements will apply to both NSPS Subpart Kb and NSPS Subpart Kc sources. Sources will be required to submit notifications and reports through EPA’s electronic reporting portal, CEDRI, and reporting will be required in this format upon finalization of the rule.
    • NSPS Subpart Kb reports and notifications in 60.115b(a), (b), and (d) will be reported via PDF upload to CEDRI.
    • NSPS Subpart Kc reports will be reported by CEDRI spreadsheet template uploads, including:
  • Initial notifications (40 CFR 60.116c(a))
  • Semiannual reports (40 CFR 60.116c(b))


Questions? Connect with our air compliance specialists.

Trihydro’s air quality and regulatory specialists remain current on changing regulations to support you in maintaining compliant operations and reporting.

Connect with us if you would like to discuss how the EPA’s proposed NSPS Subpart Kc affects your facility.

Contact Us 


John Pfeffer headshot
John Pfeffer
Senior Air Professional, Lakewood, Colorado

John has performed, supervised, and managed environmental projects in the refining and petrochemical industries for nearly 30 years. His experience includes numerous Clean Air Act compliance projects involving New Source Review (NSR) permitting, Title V Permitting and compliance, Benzene Waste Operations NESHAP (BWON), Consent Decree compliance, leak detection and repair (LDAR) program implementation and management, New Source Performance Standards (NSPS), and Maximum Achievable Control Technology (MACT) regulations.
Jay Christopher
Senior Scientist Specialist, Englewood, Colorado

Jay has over 40 years of environmental experience. Since 1990, he has specialized in air quality issues and permitting programs affecting a broad range of facility operations, with hands-on experience in both corporate headquarters and facility regulatory settings, as well as in the environmental consulting world. Jay has managed the environmental compliance program and environmental professional staff for a major refinery’s downstream businesses and is involved in regional air quality issues and national trade groups.

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