Understanding EPA’s Proposed Amendments to Subpart W
On June 30, 2023, the U.S. Environmental Protection Agency (EPA) proposed several amendments to the Greenhouse Gas Reporting Program (GHGPR). These amendments aim to improve the overall accuracy of reported methane emissions by:
Incorporating more empirical data
Including additional emission sources not previously addressed in subpart W, such as “other large release events”
Improving emission calculations
In this article we dive into 1) the interplay between these updates and the IRA Waste Emissions Charge, and 2) significant proposed changes and how they will impact your methane mitigation strategy.
Interplay with IRA Waste Emissions Charge
In August 2022, the Inflation Reduction Act (IRA) of 2022 was signed into law. With this, the Clean Air Act was amended to include a “Waste Emissions Charge” under section 136 “Methane Emissions and Waste Reduction Incentive Program for Petroleum and Natural Gas Systems”.
The “Waste Emissions Charge” specifies that the owner or operator of a facility must pay a charge on facilities that report more than 25,000 mtCO2e in accordance with reporting requirements outlined in subpart W of the GHG Reporting Program. However, without accurate emissions reporting, it will be difficult to enact the Waste Emissions Charge as prescribed by the IRA. The Clean Air Act therefore required the EPA to revise subpart W to include empirical data for emissions reporting.
The EPA’s proposed amendments to the GHGRP aim to improve the overall accuracy of methane emissions reporting. The intention is that, with these improvements, the EPA will be able to more accurately determine when to collect on the “Waste Emissions Charge”.
New Emission Sources
Other Large Release Events
Several academic studies demonstrate that bottom-up methane inventories calculated using subpart W reported facility emissions underestimate total methane emissions because they don’t include large release events such as super-emitters. These studies typically demonstrate this with data from top-down “screening” methods such as satellite, airborne, or mobile methods, which are more likely to capture intermittent large release events.
As a result, the EPA is proposing changes that would account for these discrepancies through inclusion of a new emission source category called “other large release events”. This new emission source category would include storage wellhead leaks, well blowouts, and other large, atypical release events and will apply to all facilities subject to subpart W. The proposed amendments include expanding the definition of “other large release events” to include planned releases.
The EPA is proposing that “large release events” must be reported when emissions exceed an instantaneous threshold of 100 kg/hr, or a total of 250 mtCO2e per event. These thresholds and reporting requirements apply whether the release event was intentional or not.
The expectation is that total emissions from other large release events will be quantified using advanced screening methods conducted under NSPS OOOOb (or state equivalent), or the applicable Federal plan in 40 CFR part 62. However, the EPA maintains that, as of now, top-down technologies cannot accurately quantify annual facility emissions, and therefore must be used in conjunction with other methods. They are seeking comment on how to calculate event duration from top-down data to fill this knowledge gap.
Revisions to Emissions Calculations
The proposed updates include several changes to emission calculations, ranging from new measurement methods, to requiring the use of operating conditions data (rather than estimates). We’ve summarized the main updates below:
Allow direct measurement of equipment leaks and natural gas pneumatic devices.
New calculation methods for developing site-specific emission factors for equipment leaks and pneumatic devices based on direct measurements.
Updated calculations to include empirical data such as operating conditions (for example, for large glycol dehydrators and acid gas removal units).
Updated emission factors for low and high bleed natural gas pneumatic devices and for equipment leaks from natural gas distribution sources.
For intermittent bleed pneumatics, new methods for measuring emissions in place of default emission factors that are currently used.
Allowing use of advanced screening methods for quantifying total emissions from other large release events.
Impact
The proposed updates to subpart W of the GHGRP are reflective of the “move to measurement” sweeping across the industry when it comes to methane management and mitigation. The majority of these updates involve fewer assumptions and more measurements. Not only will there be a requirement to measure more methane, but the proposed updates include other types of empirical data, such as unit-level operating conditions.
The inclusion of new emission source categories such as “other large release events” is meant to remedy the discrepancy in bottom-up and top-down inventories noted in several academic papers. How this will be implemented in practice is still to be determined. As noted by Daniel Zimmerle here, there is a question as to how frequently sites will need to be surveyed to abide by the proposed reporting thresholds.
What Next?
The proposed changes are set to come into effect January 1, 2025.
The EPA is seeking comment on several aspects of the proposed revisions. The final revision is expected to take place next year (2024).
The updates to subpart W are happening concurrently to several other changes to EPA methane rules, including Section 111 Methane Rule (expected to be finalized later in 2023), and a proposal for implementing the IRA’s waste emissions fee (expected to be proposed in Fall, 2023)
See the EPA news release on these proposed amendments here.
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