Gas production and migration in landfills and geological materials

Landfill gas, originating from the anaerobic biodegradation of the organic content of waste, consists mainly of methane and carbon dioxide, with trace s of volatile organic compounds. Pressure, concentration and temperature gr adients that develop within the landfill result in gas emissions to the atm osphere and in lateral migration through the surrounding soils. Environment al and safety issues associated with the landfill gas require control of of f-site gas migration. The numerical model TOUGH2-LGM (Transport of Unsatura ted Groundwater and Heat-Landfill Gas Migration) has been developed to simu late landfill gas production and migration processes within and beyond land fill boundaries. The model is derived from the general non-isothermal multi phase. flow simulator TOUGH2, to which a new equation of state module is ad ded. It simulates the migration of five components in partially saturated m edia: four fluid components (water, atmospheric air, methane and carbon dio xide) and one energy component (heat). The four fluid components are presen t in both the gas and liquid phases. The model incorporates gas-liquid part itioning of all fluid components by means of dissolution and volatilization . In addition to advection in the gas and liquid phase, multi-component dif fusion is simulated in the gas phase. The landfill gas production rate is p roportional to the organic substrate and is modeled as an exponentially dec reasing function of time. The model is applied to the Montreal's CESM landf ill site, which is located in a former limestone rock quarry. Existing data were used to characterize hydraulic properties of the waste and the limest one. Gas recovery data at the site were used to define the gas production m odel. Simulations in one and two dimensions are presented to investigate ga s production and migration in the landfill, and in the surrounding limeston e. The effects of a gas recovery well and landfill cover on gas mi.-ration are also discussed. (C) 2001 Elsevier Science B.V. All rights reserved.