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Joint utility proposal to adopt updated EPA MRR emission factors for compressor stations
Summary
Joint utility representatives proposed switching Appendix 2 (transmission compressor stations) to leak‑based emission factors (aligned with EPA’s May 14, 2024 MRR amendments) while keeping population‑based factors for vented pneumatics; CARB/CPUC asked utilities to file formal appendix submittals showing baseline impacts.
Representatives from PG&E, SoCalGas and Southwest Gas told the workshop that they plan to propose changes to the CPUC reporting templates for Appendix 2 (transmission compressor stations) and Appendix 5 (distribution M&R stations) to adopt the emission factors in the U.S. Environmental Protection Agency’s May 14, 2024 amendment to the Mandatory Reporting of Greenhouse Gases (MRR).
SoCalGas staff said the proposed change would replace population‑based facility emission factors for many compressor‑station components with leak‑based emission factors from the EPA MRR, while retaining population‑based factors for vented emissions from pneumatic devices (which are characterized by actuator type). The utilities said the MRR amendment provides updated component‑level emission factors and that, where companies can, they could also submit company‑specific leak‑based factors derived from sufficient sampling.
Utility presenters said they had begun preliminary sampling for company‑specific factors but had not yet collected enough representative samples to produce statistically robust factors. SoCalGas and other utilities said the EPA MRR numbers were in some cases more conservative (i.e., higher) than preliminary company data. Presenters recommended that utilities prepare formal Appendix‑2/5 submittals that document before‑and‑after baseline calculations and show how a change would affect reported emissions and the 2015 baseline.
CARB and CPUC staff reiterated the March 31, 2025 target to finalize reporting‑template revisions and invited utilities to submit proposed template language and any emission‑factor proposals promptly. Several attendees asked for background on how EPA derived its MRR factors and whether company‑specific sampling would be acceptable; utility and agency staff said the EPA methods and citation (Federal Register 89 FR 42325 and 42327, May 14, 2024) are available and that utilities may submit company‑specific factors if they document sampling and demonstrate comparability.
Staff noted that any change to emission factors would require a formal utility filing that includes the effect on the 2015 baseline and that CPUC staff would accept proposals for evaluation on a utility‑by‑utility basis.
