Two families of rules
A storage vessel can fall under the volatile organic liquid storage NSPS (Subparts Kb and Kc) or, in the crude oil and natural gas source category, the oil and gas NSPS (Subparts OOOO, OOOOa, and OOOOb). Which one depends on when the vessel was built or changed, its size, what it stores, and where it sits. Vessels built before the Kb window may fall under older Part 60 subparts not covered here.
Kb and Kc: the date window comes first
Kb and Kc split by the date construction, reconstruction, or modification commenced. Each then sets capacity and vapor pressure conditions, so you need the vessel's design capacity and the maximum true vapor pressure of the liquid as stored.
“each storage vessel with a capacity greater than or equal to 75 cubic meters (m³) that is used to store volatile organic liquids (VOL) for which construction, reconstruction, or modification is commenced after July 23, 1984, and on or before October 4, 2023.”
40 CFR 60.110b(a)“each storage vessel with a capacity greater than or equal to 20,000 gallons (gal) (75.7 cubic meters (m³)) that is used to store volatile organic liquids (VOL) for which construction, reconstruction, or modification is commenced after October 4, 2023.”
40 CFR 60.110c(a)“This subpart does not apply to storage vessels with a capacity greater than or equal to 151 m³ storing a liquid with a maximum true vapor pressure less than 3.5 kilopascals (kPa) or with a capacity greater than or equal to 75 m³ but less than 151 m³ storing a liquid with a maximum true vapor pressure less than 15.0 kPa.”
40 CFR 60.110b(b)“Storage vessels with a capacity greater than or equal to 40,000 gal (151 m³) containing a VOL that, as stored, has a maximum true vapor pressure equal to or greater than 0.5 psia (3.4 kPa).”
40 CFR 60.110c(c)(1)“Storage vessels with a capacity greater than or equal to 20,000 gal (75.7 m³) but less than 40,000 gal (151 m³) containing a VOL that, as stored, has a maximum true vapor pressure equal to or greater than 1.5 psia (10.3 kPa).”
40 CFR 60.110c(c)(2)
Exclusions that matter for oil and gas
Both subparts exclude vessels up to a stated size used for petroleum or condensate before custody transfer. For production tanks, check that exclusion first, then the oil and gas NSPS. The exemption lists also cover bulk gasoline plants and gasoline service stations; read them in full.
“Vessels with a design capacity less than or equal to 1,589.874 m³ used for petroleum or condensate stored, processed, or treated prior to custody transfer.”
40 CFR 60.110b(d)(4)“Vessels with a design capacity less than or equal to 420,000 gal (1,589.874 m³) used for petroleum or condensate stored, processed, or treated prior to custody transfer;”
40 CFR 60.110c(b)(4)
The oil and gas NSPS: which subpart by date
OOOO, OOOOa, and OOOOb each cover facilities built, modified, or reconstructed in their own window. Subpart OOOOc is different: it sets emission guidelines for existing sources, which reach a site through a state or federal plan rather than directly.
“for which you commence construction, modification, or reconstruction after August 23, 2011, and on or before September 18, 2015.”
40 CFR 60.5365“for which you commence construction, modification, or reconstruction after September 18, 2015, and on or before December 6, 2022.”
40 CFR 60.5365a“for which you commence construction, modification, or reconstruction after December 6, 2022.”
40 CFR 60.5365b“This subpart establishes emission guidelines and compliance schedules for the control of greenhouse gas (GHG) emissions from designated facilities in the crude oil and natural gas source category”
40 CFR 60.5360c
OOOO and OOOOa look at each vessel
Under OOOO and OOOOa, the affected facility is a single storage vessel with potential VOC emissions at or above the rule's threshold.
“Each storage vessel affected facility, which is a single storage vessel located in the oil and natural gas production segment, natural gas processing segment or natural gas transmission and storage segment, and has the potential for VOC emissions equal to or greater than 6 tons per year (tpy)”
40 CFR 60.5365(e)“A single storage vessel that commenced construction, reconstruction, or modification after September 18, 2015, and on or before November 16, 2020, is a storage vessel affected facility if its potential for VOC emissions is equal to or greater than 6 tons per year (tpy)”
40 CFR 60.5365a(e)(1)“a single storage vessel that commenced construction, reconstruction or modification after November 16, 2020, is a storage vessel affected facility if the potential for VOC emissions is equal to or greater than 6 tpy”
40 CFR 60.5365a(e)(2)
OOOOb looks at the tank battery
OOOOb changed the unit of analysis. The affected facility is the tank battery, and potential emissions are added across all its vessels, for VOC and for methane. A battery below both thresholds stays out only while its calculation is kept on file. Check which vessels make up the battery against the definitions in 40 CFR 60.5430b.
Adding a vessel, or replacing vessels so total capacity goes up, can make an existing battery an affected facility, and so can added throughput on the dates the rule gives. Recalculate whenever the battery changes. Once a battery is an affected facility, a later drop in its potential for VOC emissions doesn't take it out of the rule.
“Each storage vessel affected facility, which is a tank battery that has the potential for emissions as specified in either paragraph (e)(1)(i) or (ii) of this section.”
40 CFR 60.5365b(e)“Potential for VOC emissions equal to or greater than 6 tons per year (tpy) as determined in paragraph (e)(2) of this section.”
40 CFR 60.5365b(e)(1)(i)“Potential for methane emissions equal to or greater than 20 tpy as determined in paragraph (e)(2) of this section.”
40 CFR 60.5365b(e)(1)(ii)“The potential for VOC and methane emissions must be calculated as the cumulative emissions from all storage vessels within the tank battery as specified by the applicable requirements in paragraphs (e)(2)(i) through (iii) of this section. The determination may take into account requirements under a legally and practicably enforceable limit in an operating permit or other requirement established under a Federal, state, local, or Tribal authority.”
40 CFR 60.5365b(e)(2)“A tank battery with the potential for emissions below both of the thresholds specified in paragraphs (e)(1)(i) and (ii) of this section is not a storage vessel affected facility provided the owner/operator keeps records of the potential for emissions calculation for the life of the storage vessel or until such time the tank battery becomes a storage vessel affected facility because the potential for emissions meets or exceeds either threshold specified in either paragraph (e)(1)(i) or (ii) of this section.”
40 CFR 60.5365b(e)““Modification” of a tank battery occurs when any of the actions in paragraphs (e)(3)(ii)(A) through (D) of this section occurs and the potential for VOC or methane emissions meet or exceed either of the thresholds specified in paragraphs (e)(1)(i) or (ii) of this section.”
40 CFR 60.5365b(e)(3)(ii)“A storage vessel is added to an existing tank battery;”
40 CFR 60.5365b(e)(3)(ii)(A)“One or more storage vessels are replaced such that the cumulative storage capacity of the existing tank battery increases;”
40 CFR 60.5365b(e)(3)(ii)(B)“A storage vessel affected facility that subsequently has its potential for VOC emissions decrease to less than 6 tpy shall remain an affected facility under this subpart.”
40 CFR 60.5365b(e)(4)
How OOOOb wants the potential calculated
OOOOb sets the method and the throughput basis: a generally accepted model or calculation that accounts for flashing, working, and breathing losses. An enforceable limit can be taken into account, but from the date the rule gives, only if it contains the listed elements. The guide on writing a synthetic minor limit walks through them.
“For each tank battery located at a well site or centralized production facility, you must determine the potential for VOC and methane emissions within 30 days after startup of production, or within 30 days after an action specified in paragraphs (e)(3)(i) and (ii) of this section, except as provided in paragraph (e)(5)(iv) of this section. Beginning January 22, 2027, the potential for VOC and methane emissions must be calculated using a generally accepted model or calculation methodology that accounts for flashing, working, and breathing losses, based on the maximum average daily throughput to the tank battery determined for a 30-day period of production.”
40 CFR 60.5365b(e)(2)(ii)“Beginning January 22, 2027, or upon startup, whichever is later, for purposes of determining the applicability of a storage vessel tank battery as an affected facility, a legally and practicably enforceable limit must include the elements provided in paragraphs (e)(2)(i)(A) through (F) of this section.”
40 CFR 60.5365b(e)(2)(i)
What to collect for each vessel
Gather these before reading the rules:
- Design capacity, and the tanks manifolded together
- Liquid stored and its maximum true vapor pressure as stored, with the basis
- Dates of construction, reconstruction, and modification
- Location: well site, centralized production facility, compressor station, processing plant, or elsewhere
- Where custody transfer happens
- Throughput, how it is measured, and the projected maximum
- Vapor recovery and control devices, and what is routed to them
Sources
- 40 CFR 60.110b: Subpart Kb applicability (eCFR)
- 40 CFR 60.110c: Subpart Kc applicability (eCFR)
- 40 CFR 60.5365: Subpart OOOO applicability (eCFR)
- 40 CFR 60.5365a: Subpart OOOOa applicability (eCFR)
- 40 CFR 60.5365b: Subpart OOOOb applicability (eCFR)
- 40 CFR 60.5360c: Subpart OOOOc purpose (eCFR)
This guide explains how programs fit together. Thresholds, limits, and dates appear only in the quoted text, linked to its source; read the full provision before relying on it.
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