Modeling landfill gas generation and migration in sanitary landfills and geological formations

Biodegradation of the organic part of refuse disposed at landfills generates large quantities of methane and carbon dioxide, referred to as landfill gas. Both gases are considered contributors to global climate warming while methane is also an explosive gas in concentrations of 5--15% by volume. Most of the produced gas is emitted directly to the atmosphere while smaller quantities migrate beyond landfill boundaries through the adjacent soils. The numerical model TOUGH2-LGM was developed to simulate landfill gas production and migration processes within and beyond landfill boundaries. The model is derived from the original version of TOUGH2 (Pruess, 1987 and 1991).;TOUGH2-LGM considers migration of four fluid components (water, air, methane and carbon dioxide), and one energy component (heat) in partially saturated media. The four fluid components are present in both gas and liquid phases. The gas and the liquid phase flows are dependent on the water and gas saturations and the corresponding relative permeabilities. The model incorporates gas-liquid partitioning of all of fluid components by means of dissolution and volatilization. In the gas phase, migration of the fluid components is simulated by advective and diffusive mechanisms. In the liquid phase, only the advective flux is considered. Heat transfer occurs by conduction through the porous media and by fluid migration in both phases.;Landfill gas production is modeled as a simple exponentially decreasing function of time. The overall kinetic coefficient was adjusted according to the observed recovery rates at the C.E.S.M. landfill site. It is estimated that one ton of disposed refuse produces 172 M3 of landfill gas. The methane to carbon dioxide production ratio is 55% : 45% by volume.;The numerical simulator was successfully used for modeling gas migration at two landfill sites: the C.E.S.M. landfill at the City of Montreal and the St-Etienne-des-Gres landfill. The combination of field data measurements and numerical simulations provided the best description of the migration mechanisms at both landfill sites. In this way, the actual field conditions were extended to future scenarios for assessing the rate of gas migration and the effectiveness of the current recovery systems. The obtained results are matching the observed field data with high precision.