Geoenvironmental assessment of climate impacts from landfill gas emissions

Abstract

An extensive field investigation was conducted to determine emissions of 80 individual landfill gas species from 3 cover categories (daily, intermediate, and final) at 5 California (USA) landfills over 2 main seasons (wet and dry). The gases included 15 principal anthropogenic greenhouse gases (methane, nitrous oxide, and 13 F-gas species) and 65 non-methane volatile organic compounds (NMVOCs). Emissions were measured using the static flux chamber method. In addition, field and laboratory tests were conducted to determine geotechnical index properties of the covers. Results are presented for flux and baseline emissions as well as for direct and indirect climate forcing emissions (CO2-eq.) of the chemicals. Positive flux of a given chemical at a given landfill varied by up to 8 orders of magnitude and similarly, between landfills by up to 8 orders of magnitude. Direct emissions varied from 480 to 38,000 Mg CO2-eq./yr, where emissions per m3 waste in place ranged from 0.0004 to 0.013 Mg CO2-eq./m3-yr and per ha of landfill area ranged from 4.8 to 1320 Mg CO2-eq./ha-yr. Flux and emissions decreased as the cover soils varied from coarser to finer materials, clay content of cover soils increased, and with increasing composite parameters representing combined void ratio and cover thickness, total cover solids, and combined gas-phase tortuosity and thickness. These parameters and the associated numerical thresholds identified in this paper can be used to inform improved engineering design, construction, and operations of landfill covers to mitigate gas emissions and limit climate change effects from landfills.