| A study was conducted to determine the emission rate of greenhouse gases (GHGs) from individual onsite septic systems used for the management of domestic wastewater. The emission rates of methane, carbon dioxide, and nitrous oxide gases were determined from eight septic systems. Gas emission rates from septic tanks and soil dispersal systems were determined using a static flux chamber method. The mass flow of gases moving through the household drainage and vent system were also determined using a technique developed for measurement of gas flow and concentration at clean out ports. There was general agreement in the methane emission rate for the flux chamber and vent system methods. Several sources of variability in the emission rates were also identified.;The primary source of methane was the septic tank, whereas the principal source of carbon dioxide and nitrous oxide emissions was the soil dispersal system. Methane concentrations from the soil dispersal system were found to be near ambient concentrations, similarly negligible amounts of nitrous oxide were found in the septic tank. All emissions originating in the soil dispersal system were discharged through the building vent as a result of natural, wind-induced flow. The gaseous emission data were determined to be geometrically distributed. The geometric mean and standard deviation (sg) of the total atmospheric emission rates for methane, carbon dioxide, and nitrous oxide based on samples from the vent system were estimated to be 10.7 (sg = 1.65), 335 (sg = 2.13), and 0.20 (sg = 3.62) g/capita d, respectively. The corresponding total CO2 equivalent (CO2e) of the GHG emissions to the atmosphere, is about 0.24 tonne CO2e/capita·yr. |
