Greenhouse Gas Emissions from Septic Systems in New York State

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Microbiology

Background:

• Onsite septic systems utilize microbial processes for waste treatment, potentially releasing greenhouse gases (GHGs).
• Current U.S. Environmental Protection Agency (USEPA) estimates for septic system GHG emissions are limited and based on a single study, leading to an unclear contribution to the overall GHG budget.
• Methane (CH4) is the primary GHG considered in existing estimates, neglecting other significant emissions.

Purpose of the Study:

• To quantify and compare GHG emissions from septic system leach fields and roof vents.
• To assess the contribution of different septic system components to air pollution.
• To inform revisions of current environmental regulations and emission estimation methods.

Main Methods:

• Quantified fluxes of methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) using a static chamber method at eight septic systems.
• Measured gas emissions from both the soil over leach fields and the roof vent.
• Calculated total GHG emissions in CO2-equivalents per capita per year.

Main Results:

• The roof vent was identified as the primary source of septic system gas emissions.
• Leach fields were found to be a significant source of nitrous oxide (N2O) fluxes.
• Total estimated GHG emissions from septic systems represent approximately 1.5% of an individual's annual carbon footprint in the U.S.

Conclusions:

• Septic systems are a notable source of GHGs, including N2O, which is not currently recognized by the USEPA.
• Biological processes within leach field soils influence the type and quantity of emitted gases.
• Further research is needed across diverse climatic and geographic settings to refine emission estimates and update regulatory guidance.