EPA Subpart W · Midstream Operations
Auto-fill: NG = 1,020 Btu/scf | Propane = 2,516 Btu/scf | Diesel = 137,000 Btu/gal
Understand GHG reporting regulations, Subpart W requirements, emission factors, and reduction strategies
EPA 40 CFR Part 98 Subpart W covers greenhouse gas reporting for petroleum and natural gas systems. Facilities emitting 25,000 metric tonnes CO2e per year or more must report annually. Sources include combustion equipment, venting, flaring, fugitive emissions, pneumatic devices, dehydrators, and compressor seals.
EPA currently requires IPCC AR4 values: methane GWP of 25 and N2O GWP of 298 for Subpart W reporting. IPCC AR5 uses GWP of 28 for methane. The 20-year GWP for methane is 80-84, reflecting its stronger short-term warming effect.
EPA provides default emission factors per component type and service. For example, gas service valves emit 0.0268 kg/hr, connectors 0.0006 kg/hr, and open-ended lines 0.0165 kg/hr. Multiply by component count and 8,760 hours/year for annual emissions. LDAR programs can reduce these by 40-90%.
The reporting threshold under Subpart W is 25,000 metric tonnes of CO2e per year. Facilities exceeding this threshold must report to EPA annually via the electronic Greenhouse Gas Reporting Tool (e-GGRT). Even below the threshold, state regulations may impose additional requirements.