At an oil and gas site, a well and a tank battery may have different construction and modification histories. Those differences can affect which emissions requirements apply, even at the same location. A qualifying modification can bring one designated facility under a newer federal standard without necessarily changing the requirements for other equipment at the site. For environmental teams, understanding those distinctions is important when determining which monitoring, reporting, and recordkeeping obligations apply.
EPA's emissions guidelines under 40 CFR part 60, subpart OOOOc address certain existing oil and gas facilities. Coverage depends on the designated-facility category and other applicability conditions, including whether construction, modification, or reconstruction commenced on or before December 6, 2022. The guidelines do not directly impose those requirements on operators. Instead, operators follow the applicable state or tribal implementing plan, or a federal plan where EPA implements one (§ 60.5374c).
Whether an OOOOc implementing plan is approved and effective also matters. Equipment may remain subject to earlier federal standards, including NSPS OOOO or OOOOa, alongside existing state requirements. On October 29, 2026, EPA proposed further revisions to the new-source standards and these guidelines. That proposal is not a final amendment.
Under § 60.5375c, plans implementing OOOOc address designated facilities that commenced construction, modification, or reconstruction on or before December 6, 2022, that are of a type listed in Table 1, and that are not exempt under § 60.14(e). A listing in Table 1 still leaves the category definition to be checked. EPA's model rule defines these designated facilities in § 60.5386c. The implementing plan is what determines which definitions and requirements the operator follows.
In that model rule, a well designated facility is a single well. A storage vessel designated facility is a tank battery with potential methane emissions of at least 20 tons per year, counted across the vessels in the battery. A tank battery consists of storage vessels connected for liquid transfer, and it may contain just one vessel (§ 60.5430c). Fugitive-emissions components are the collection of those components at a well site, a centralized production facility, or a compressor station.
The difference shows up in an equipment inventory. An individual tank record may not show which vessels are connected for liquid transfer, or what their combined potential methane emissions are. Both matter when determining whether the tank battery meets the model-rule definition of a designated facility. The operator checks those records against the designated-facility definition adopted by the applicable plan.
Once an OOOOc plan is approved and in effect, the operator reviews what that plan requires for each designated facility: the emissions standard, the compliance date, the testing or monitoring, and the records that show compliance. The model rule, in §§ 60.5385c through 60.5430c, contains the presumptive standards and the monitoring, recordkeeping, and reporting a state can use when it writes the plan (§ 60.5376c). A state may adopt the model rule, demonstrate that alternative standards satisfy the guidelines, or apply a less stringent standard where the conditions in § 60.5365c are met.
Equipment inventories, construction and modification records, and existing permits are a practical starting point. They can show which units may be covered and which standard may apply. From there, the operator checks the applicable federal standards and any effective implementing plan, alongside existing state requirements, for the compliance dates and the obligations that govern each unit.
An approved plan does not automatically replace an earlier federal standard. An affected facility subject to NSPS OOOO or OOOOa must continue complying until it begins complying with a more stringent requirement for that same affected facility in an approved and effective state or federal plan that implements OOOOc (§ 60.5365 and § 60.5365a). A modification or reconstruction after December 6, 2022 that makes the facility subject to OOOOb is a separate transition.
State methane limits and other air-emissions requirements can continue to apply, including where no OOOOc plan is in effect. The operator accounts for those alongside the federal standard when deciding which obligations govern the equipment.
A designated facility modified after December 6, 2022 becomes subject to NSPS OOOOb if the change meets the regulatory definition of modification, and the state or tribal plan no longer applies to that facility (§ 60.5375c(b)). Reconstruction commenced after December 6, 2022 can also bring the affected facility under OOOOb (§ 60.5365b). From that point, the requirements depend on the affected-facility category under OOOOb. For an affected facility that has OOOOb fugitive-emissions requirements, Validere's guide covers the monitoring methods, survey frequencies, and repair obligations.
Physical or operational changes made primarily to comply with the state or tribal plan do not qualify as modifications under OOOOb when construction of the designated facility commenced on or before September 9, 2024 (§ 60.5375c(c)). The exception does not cover every project carried out for compliance. Other physical or operational changes may still qualify as modifications under OOOOb.
When a qualifying modification changes the federal standard for that designated facility, the operator reassesses the monitoring, reporting, and recordkeeping that apply to it.
If a state does not have an approved and effective OOOOc plan, the operator checks whether EPA has implemented an applicable federal plan. If neither an approved and effective state or tribal plan nor an effective federal plan applies, OOOOc's presumptive standards do not independently impose requirements on the operator. Where NSPS OOOO or OOOOa already applies to an affected facility, that standard continues, and state air-emissions requirements can apply as well. A plan that has only been submitted, or that EPA has proposed to approve, is not yet an effective plan.
EPA publishes those actions in the Federal Register and codifies approved state plans and applicable federal plans in 40 CFR part 62. A recent action can appear in the Federal Register before part 62 reflects it.
Once the applicable requirements are established, operators need to manage any required inspections, document field findings, track corrective actions, and maintain supporting records. Validere's environmental compliance software helps energy operators manage inspection schedules, field findings, and corrective actions.