(March 18, 2021) – NACWA submitted comments March 15 on EPA’s Draft Inventory of US Greenhouse Gas Emissions and Sinks:1990-2019 as part of the public review process, following up on the comments submitted during the expert review period. The annual Inventory provides nationwide estimates for greenhouse gas (GHG) emissions for different sectors, including wastewater treatment, and is intended to be used only for informational purposes.

The wastewater treatment category in the Inventory includes publicly owned treatment works (POTWs), septic systems, and industrial wastewater treatment systems. NACWA has reviewed and commented on the POTW emissions estimates in the Inventory since 2007, recommending revisions to characterize the sector’s emissions more accurately.

This year’s Inventory used a new protocol developed by the Intergovernmental Panel on Climate Change (IPCC) for calculating wastewater emissions, resulting in substantial changes from previous years. The magnitude of municipal wastewater emissions has increased from previous years but is still in an expected range based on emissions research.   

NACWA recommended that EPA consider several changes to more accurately characterize emissions from municipal wastewater treatment processes. Most importantly, the new IPCC guidance eliminated the different emissions factors depending on whether treatment plants use nitrification/dentrification processes. NACWA encouraged EPA to reinstate emission factors that account for the use or absence of the nitrification/denitrification process, and to develop emission factors that are specific to U.S. utilities whenever possible. 

NACWA members with questions or comments about the Inventory should contact Cynthia Finley, NACWA’s Director of Regulatory Affairs.