NACWA submitted comments March 17 on EPA’s Draft Inventory of US Greenhouse Gas Emissions and Sinks: 1990-2020 as part of the public review process. 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.

In its comments, NACWA recommended that EPA develop US-and treatment-specific methodologies and emissions factors, particularly for nitrous oxide emissions.  EPA began using new guidance last year from the Intergovernmental Panel on Climate Change (IPCC) to estimate emissions.  Unlike previous IPCC methods, the new guidance did not account for whether treatment plants use nitrification/denitrification processes.  This process can significantly affect the nitrous oxide emissions, and NACWA stated that EPA should use US-specific factors to account for the presence or absence of this process at different treatment plants. 

NACWA agreed with EPA’s planned improvements for subsequent Inventories, including investigation of how GHG emissions depend on receiving water characteristics, review of biosolids data, and updates to the amount of wastewater produced per capita in the US. 

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