Bridger Photonics’ Comments on EPA’s Subpart W Proposed Rule

A Summary of Bridger’s Comments on EPA’s Proposed Greenhouse Gas Reporting Rule for Petroleum and Natural Gas Systems

In July of 2023, the EPA proposed revisions to the Greenhouse Gas Reporting Program for Petroleum and Natural Gas Systems (Proposed Rule; commonly known as “Subpart W”).

Bridger Photonics (Bridger) submitted comments on the proposal that included recommendations aiming to increase the accuracy of methane emissions reporting while reducing complexity. Bridger provided five recommendations:

1. Remove incentives to use less effective emissions monitoring technology.
2. Fund the development of regional measurement-based methane emissions inventories and use findings to strategize and track emissions reductions.
3. Allow operators to demonstrate low emissions at their reporting facilities by developing facility-level measurement-based methane emissions inventories.
4. Create a pathway to approve and update methods for developing measurement-based methane emissions inventories.
5. Allow operators to use direct measurements to report gathering pipeline emissions.

The following is a summary of Bridger’s comments. Access to the full version can be found here, or at the bottom of this page.

Remove Incentives to Use Less-Effective Emissions Monitoring Technology 

The proposed rule highlights how a significant amount of emissions come from sources not currently accounted for in the current rule. The Proposed Rule works to address this problem by adding an “other large release event” source to reporting, which is intended to cover a variety of unexpected emissions. In order to determine the presence of “other large release events,” operators must consider any credible information which includes detections from advanced methane sensing technologies—whether they are used on a voluntary basis or as part of regulatory compliance under EPA’s OOOOb/c regulations.

Research has shown that advanced methane sensing technology can detect remarkably greater volumes of emissions compared to OGI and Method 21. As a result, using advanced technology may result in more frequent identification of large release events. The pending Inflation Reduction Act’s (IRA) “waste methane emissions charge” will mean greater fines for greater volumes of emissions under Subpart W. In turn, the proposed other large release reporting causes the unintended consequence of incentivizing operators to use less-effective emissions sensing technologies. Using less effective technologies could result in inaccurate and biased inventory records. 

Instead of attempting to ensure that Subpart W reporting is accurate by relying on a patchwork of unproven methodologies to capture more emissions events, we urge the EPA to follow the example set by Colorado’s Greenhouse Gas Intensity Verification Rule. Details on this rule can be found in our full comment letter. 

Fund the Development of Regional Measurement-Based Inventories

The IRA charged the EPA to “revise the requirements of Subpart W to ensure that reporting under Subpart W (and corresponding waste emission charges) is based on empirical data, [and] accurately reflects the total CH4 emissions (and waste emissions) from the applicable facilities…” However, the current proposed revisions will not result in an accurate reflection of methane emissions. 

The best way to ensure methane emissions reported under Subpart W are accurate is to base reporting on emissions inventories that are founded in direct measurements. Furthermore, developing inventories with equipment-level resolution would allow the EPA to identify and reconcile discrepancies between the Subpart W bottom-up model and the measured magnitude of emissions. Not only does this approach enable the nation to determine and eliminate true emissions drivers, but it also provides an avenue to accurately benchmark emissions and track reductions as inventories are updated with new data.

Additionally, because of the differing emissions profiles between U.S oil and gas production basins, it’s essential that separate inventories are developed for different reporting jurisdictions. 

Allow Operators to Demonstrate Low Emissions at Their Reporting Facilities

If an operator wishes to demonstrate that their Subpart W reporting facility has reduced methane emissions, they should be able to do so using the best available, scientifically rigorous approaches. The methods for developing regional measurement-based emissions inventories can be extended to individual reporting facilities because the fundamental principles are the same for both size scales. The EPA should allow measurement-based inventory development methods to be approved for calculating emissions both at the regional scale and at the scale of individual Subpart W reporting facilities.

Create a Pathway to Approve and Update Methods for Developing Measurement-Based Inventories

Methods for developing measurement-based methane emissions inventories involve both (a) frameworks for using measurement data and (b) technologies and technology deployment used to generate the measurement data. Robust frameworks to determine methane emissions inventories using direct measurement data already exist. Therefore, Subpart W should provide a pathway to approve frameworks for determining emission inventories as well as a pathway to approve suitable technologies to be used within the approved frameworks. 

Any data brought into an approved inventory framework should correspond to a representative sample of infrastructure as demonstrated by quantitative evaluation. Sampling should correctly represent different equipment classes, production types and volumes, site types, site ages, and operating companies (in the case of regional inventories). Furthermore, approved frameworks should:

• Include protocols to eliminate systematic errors by accounting for intraday variation in emissions and seasonal changes.
• Include protocols to scale measurements from limited sample sets to the complete population of infrastructure in the region and to annualize emissions.
•  Include protocols to integrate data appropriately considering measurement technology detection sensitivity, and quantification uncertainty.
• Include protocols to characterize uncertainty due to spatial variation of emissions and variation in emissions over time. 

For a technology (and its deployment approach) to be approved for emissions inventory measurements, it should meet the following performance criteria:

• It must have sensitive emissions detection to ensure significant emissions sources are not unaccounted for (the less sensitive the technology, the more exterior data elements must be incorporated in the inventory, which opens the door to additional sources of error). A sensitivity requirement of ~2 kg/h with >90% probability of detection is recommended based on existing work.
• The technology must have refined detection sensitivity models to determine missed emission events. 
• The technology must provide accurate quantification of aggregate emissions.
• The technology must have refined error models to reduce measurement bias and correctly report instrument quantification uncertainty.
• The technology must be resilient towards systematic sources of error such as incomplete spatial coverage and diminished sensitivity under conditions of low ambient light. 
• The application of a technology and its deployment within a framework must be validated for repeatability and consistency through replicate inventory assessments.  

Including a defined pathway to approve frameworks and technologies to develop regional and facility-level measurement-based emissions inventories would provide confidence and transparency for reporting and allow for emissions assessment methods to be continually improved.

Allow Operators to Use Direct Measurements to Report Gathering Pipeline Emissions

The Proposed Rule currently relies entirely on emissions factors for reporting gathering line emission and lacks the option to use direct measurements to demonstrate reduced emissions. We urge the EPA to give operators the option to use monitoring and direct measurement surveys to report on these emissions. The EPA should align gathering pipeline emissions reporting with other EPA and PHMSA provisions by allowing operators to use EPA OOOOb-compliant advanced technologies, Subpart W-compliant monitoring and measurement methods, and suitable technologies used for PHMSA-compliant gas pipeline leak screening requirements. 

Read Bridger’s full comment letter here.