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U.S. EPA Finalizes Leak Detection Methodology Revisions to Subpart W of the GHG Reporting Rule

Posted: December 12th, 2016

Author: All4 Staff 

Back in March 2016, Megan wrote an article about the proposed alignment between the oil and gas industry leak requirements under 40 CFR Part 98 Subpart W – Mandatory Greenhouse Gas (GHG) Reporting for Petroleum and Natural Gas Systems (Subpart W) and 40 CFR Part 60 Subpart OOOOa – Standards of Performance for Crude Oil and Natural Gas Production, Transmission and Distribution (Subpart OOOOa).  The goal of the proposed amendments was to incorporate certain Subpart OOOOa leak detection requirements into Subpart W.  On November 30, 2016, U.S. EPA published a final version of those revisions to the Federal Register.  Read on to find out what the final rule changes entail.

Who Is Impacted By These Changes?

The Subpart W revisions affect companies required to quantify and report leak emissions under Subpart W and, in particular, those companies with well sites and compressor stations subject to fugitive emissions monitoring requirement under Subpart OOOOa.

When Is It Changing?

The Subpart W revisions are effective January 1, 2017.  Therefore, Subpart W leak surveys and emissions calculations for calendar year 2017 must be conducted in accordance with the new requirements.

What Is Changing?

The final revisions to Subpart W are generally consistent with the revisions proposed in early 2016.  Four main aspects of Subpart W are being revised relating to leak provisions:

  1. Equipment Leak Calculation Methodologies
    For well sites and compressor stations required to conduct fugitive emissions monitoring under Subpart OOOOa, companies will now be required to use a GHG emissions calculation methodology that is based on subpart OOOOa leak monitoring methods.  Although new calculation methodology and equipment leak survey requirements are being added to Subpart W, the new requirements can also be met by counting the number of components with fugitive emissions identified during Subpart OOOOa leak surveys.For sources not subject to Subpart OOOOa well site or compressor station fugitive emissions standards, the Subpart W requirements are largely unchanged:

    • If facilities are currently required to conduct equipment leak surveys under Subpart W for these sources, they will remain subject to this requirement under the revised rules and may now use any monitoring method specified in 40 CFR §98.234(a), including two new methods added to 40 CFR §§98.234(a)(6) or (7).  However, if facilities elect to use either of the two new methods, all components regulated under Subpart OOOOa must be surveyed for these facilities.
    • If facilities are currently required to estimate GHG leak emissions based on component population counts, facilities may continue to use this methodology or, optionally, may elect to estimate emissions based on leak surveys.
    • Finally, in the proposed rule, U.S. EPA considered requiring that facilities in the Onshore Natural Gas Processing industry segment also use Subpart OOOOa leak surveys for Subpart W reporting.  However, in the preamble to the final rule, U.S. EPA indicated that they are delaying finalizing this requirement while completing their review of comments received on this aspect of the proposed amendments.
  2. Subpart W Leak Monitoring Methods
    The Subpart W revisions add two new leak monitoring methods: 1) optical gas imaging (OGI) as specified in Subpart OOOOa; and 2) the use of Method 21 as in Subpart OOOOa, which assumes a lower leak definition of 500 ppmv.  The addition of these two methods allows facilities to directly use the results from Subpart OOOOa leak surveys in Subpart W GHG reporting.  Facilities that are not required, and do not elect, to use the two new methods can continue using the existing leak monitoring methods in 40 CFR §98.234(a), including using a Method 21 leak definition of 10,000 ppmv.
  3. Regulated Component Types
    Not all components included in the Subpart OOOOa definition of fugitive emissions were regulated under the leak provisions of the previous version of Subpart W.  In the revisions to Subpart W, U.S. EPA is aligning the Subpart W leak components with the Subpart OOOOa definition of fugitive emissions with certain exceptions where Subpart OOOOa components are regulated under another Subpart W source type (e.g., certain compressor vents, thief hatches and other openings on storage tanks).
  4. Leaker Emissions Factors
    Subpart W emissions calculations for leaking components are based on emissions factors applied to the number of leaks identified for each component type during leak surveys.  As discussed above, the revisions to Subpart W increase the number of components that may be subject to leak survey requirements.  Therefore, U.S. EPA is adding new leak emissions factors so that emissions can be estimated for the new regulated components.
  5. Reporting Requirements
    U.S. EPA is revising Subpart W reporting requirements to include leak survey information for those facilities that will be newly-required to use Subpart OOOOa methods or survey data for GHG emissions reporting purposes or that elect to do so voluntarily.  In addition, U.S. EPA is also requiring reporting of additional information for facilities that utilize the new leak monitoring methods added to Subpart W.

ALL4 has extensive experience assisting oil and gas clients with GHG emissions calculations and reporting, and can help you navigate the new rule requirements.


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