Evaluation of Greenhouse Gas Emissions from Septic ... - Geoflow

Table 5-2. Results of the Mass Balance Analysis on the Emission Rates from Septic Systems.Note: All of the Atmospheric Gas Emission Rates from These Two Systems were from the Building Vent.Gas emission rate, g/capita·day aSite CH 4 CO 2 N 2 O1 8.4 527.0 0.377 13.4 93.5 0.04Average 11.2 310.2 0.20aThe reported values correspond to averages from all the ventmeasurements at each site and can be found in the Appendix H.5.2.3 Mass Balance in the Soil Dispersal SystemTo determine the fate of carbon present in the septic tank effluent, a mass balanceanalysis in the soil dispersal system was performed. The input of carbon to the system can beestimated from the COD of the septic tank effluent. The carbon dioxide equivalent of COD wasdetermined using a stoichiometric approach where domestic wastewater is represented by thecompound C 10 H 19 O 3 N (Metcalf and Eddy, 2003). The calculation of CO 2 production from CODoxidation is shown in Appendix I.As discussed previously, direct atmospheric emissions of GHGs from the soil dispersalwere determined to be insignificant. The discharge of carbon to the groundwater is assumed to beinsignificant. The amount of carbon leaving the soil dispersal system can therefore be estimatedby the vent samples obtained from V-1-2 as shown in Figure 5-7. Based on the system carbonbalance, the carbon dioxide equivalent of the COD should be approximately equal to the CO 2leaving the soil dispersal system through the ventilation system.Figure 5-7. Mass Balance on the Soil Dispersal System.Evaluation of Greenhouse Gas Emissions from Septic Systems 5-9