Characterization of Methane Flux and Oxidation at a Solid Waste Landfill

Methane emissions were measured at several locations at a typical solid waste facility using a static chamber technique. At the entire facility, methane flux varied from –13.6 to 1,755 g m^–2 day^–1. The flux data had an arithmetic mean value of 71.3 g m–2 day–1 and a geometric mean value of 18.6 g m^–2 day^–1. At this site, methane emission was generally lower on the side slopes relative to the flat areas of the landfill. The spatial variability of methane flux was characterized by point kriging and inverse distance weighing (IDW) in an intensive study of a 61×61-m area. The geospatial means in this area obtained by both methods were almost identical (20.9 versus 20.8 g m^–2 day^–1). These geospatial means for the area were also similar to the arithmetic mean (24.5 g m^–2 day^–1), but 3.4 times the geometric mean (6.5 g m^–2 day^–1). Methane oxidation was evaluated at the surface of the landfill and at several depths within the cover soil using stable isotope techniques. The 13C of CH4 averaged –55.4% in the anoxic zone. Methane collected in chambers and in surficial soil probes exhibited more 13C enriched values, ranging from –55.4 to –34.5%, due to the preferential uptake of 12CH4 by methanotrophic bacteria. Methane oxidation at the landfill averaged 22% and occurred in the upper 70 cm of the landfill cover soil. Oxidation occurred in all tested locations of the landfill and for all ages of buried waste.