A comprehensive field investigation was conducted at Potrero Hills Landfill (PHL) located in Suisun City, California to quantify emissions of twelve (hydro)chlorofluorocarbons (i.e. F-gases). The specific target constituents for this study included CFC-11, CFC-12, CFC-113, CFC-114, HCFC-21, HCFC-22, HCFC-141b, HCFC-142b, HCFC-151a, HFC-134a, HFC-152a, and HFC-245fa. The majority of the F-gas emission studies have been conducted outside of the United States and very limited field landfill emission data are available in the United States. Because of historical usage of blowing agents in insulation foams including CFC-11, HCFC-142b, HFC-134a, and HFC-245fa, models reported in literature predicted high F-gas emissions from a landfill environment, but very limited field data are available to verify such predictions.
In this investigation, the surface flux of the twelve F-gases, methane, and carbon dioxide was quantified from various landfill cover systems and in areas with different waste ages, waste heights, and cover thicknesses at Potrero Hills Landfill. In addition, destruction efficiencies for the twelve F-gases were determined based on inlet and outlet concentrations of the onsite flare system. Lastly, the surface flux values were scaled up to a facility-wide emission value to estimate the total fugitive emissions from the landfill.
The F-gas flux values for the daily covers were in the 10 -8 to 10-1 g m-2 day -1 range and 10-7 to 10-2 g m-2 day-1 range for the wet and dry season, respectively. The F-gas flux values for the intermediate covers in the -10-6 to 10-4 g m-2 day-1 range and -10-6 to 10-4 g m-2 day-1 range for the wet and dry season, respectively. The F-gas flux values for the final covers were in the 10-7 to 10-5 g m-2 day-1 range and -10-7 to 10-6 g m-2 day-1 range for the wet and dry season, respectively. F-gas fluxes for the final covers had the highest number of below detection limit cases as well as lower than R2 threshold cases. Thest F-gas fluxes were measured from daily cover system constructed with auto shredder residue (i.e. auto fluff) for the both the wet and dry seasons. The highest fluxes were measured for CFC-11, HCFC-21, and HCFC-141b in the wet season and for CFC-11, HCFC-141b, and HFC-134a in the dry season across the seven cover locations.
Lower level of variation was observed for methane and carbon dioxide with flux values ranging over five orders of magnitude for the seven tested locations. The methane flux values for the daily covers were in the 10-2 to 10+1 g m-2 d-1 range and 1 to 10+1 g m-2 day-1 range for the wet and dry season, respectively. The carbon dioxide flux values for the daily covers were in the -10+1 to 10+2 g m-2 day-1 range and -10+1 to 10+1 g m-2 day-1 range for the wet and dry season, respectively. The methane flux values for the intermediate covers were in the -10-2 to 10+1 g m-2 d-1 range and -10-3 to 10+1 g m-2 day-1 range for the wet and dry season, respectively. The carbon dioxide flux values for the intermediate covers were in the 1 to 10+2 g m-2 day-1 range for both seasons. The methane fluxes for the final cover were -10 -3 g m-2 day-1 and 10-4 g m-2 day-1 for the wet and dry season, respectively. The carbon dioxide flux values for the final cover were in the 10+1 g m-2 d-1 range and 1 to 10+1 g m-2 day-1 range for the wet and dry season, respectively. Negative flux values were typically observed during the wet season and at the intermediate and final covers.
The destruction efficiencies for the twelve F-gases were above 99.5% for the onsite flare. Highest F-gas raw gas concentrations were measured for HFC-134a while the lowest F-gas concentration was measured for CFC-113. The F-gas concentrations in the raw gas ranged from 103 to 106 pptv. Similar to what has been reported in the literature, the landfill gas flare system was an efficient abatement device in controlling F-gas emissions.
The surface emission measurement values from the field investigation were scaled up to estimate facility-wide fugitive emission values using the relative surface areas of the daily, intermediate, and final cover distributions in the landfill. The total fugitive emissions from the landfill including twelve F-gases, methane, and carbon dioxide ranged from 6,900 to 94,000 CO2E tonnes per year during the wet season, from 21,000 to 47,000 CO2E tonnes per year during the dry season, and from 13,000 to 75,000 CO2E tonnes per year during the year, prorated by the season (representing weighted average of 58% wet season emission rate and 42% dry season emission rate in a 12-month calendar year). The total fugitive F-gas emissions ranged from 1,600 to 4,800 CO2E tonnes per year during the wet season, from 140 to 600 CO2E tonnes per year during the dry season, and from 1,000 to 3,000 CO2E tonnes per year, prorated by the season. The total fugitive methane emissions ranged from 530 to 75,000 CO2E tonnes per year during the wet season, 17,000 to 35,000 CO2E tonnes per year during the dry season, and from 7,500 to 58,000 CO2E tonnes per year, prorated by the season. The total fugitive carbon dioxide emissions ranged from 5,000 to 14,000 CO2E tonnes per year during the wet season, 4,200 to 12,000 CO2E tonnes per year during the dry season, and from 4,500 to 13,000 CO2E tonnes per year, prorated by the season. In comparison to the total fugitive emission value derived from the first-order decay (FOD) model reported by USEPA and the total fugitive emission values calculated using waste-in-place (WIP) – landfill gas correlation equation presented in Spokas et al. (2015), the field-derived methane emission values were one to three orders of magnitude lower
