Landfill Gas Migration Modelling – a Prequiste for Determining Environmentally Compatible Gas Generation Rates

SUMMARY: Landfills containing organic matter pose an environmental risk for many decades. This is also the case for the landfill Heferlbach, which has been filled until 1974 with more than 200,000 tons of waste. Since no liners have been installed at this site, landfill gas generation represents a potential hazard to the surrounding environment. In particular, the risk for methane migration into adjacent buildings was the main reason for remediating the landfill via in-situ aeration (currently ongoing). This paper aims to evaluate the risk of methane migration/accumulation in the surroundings of landfills. Thereto a 2-dimensional mathematical model allowing for simulating convective, dispersive and diffusive transport of landfill gas has been developed and subsequently applied. The modelling results demonstrate that landfill gas migration is to a large extent driven by diffusion and thus highly sensitive to the air filled porosity of the surrounding subsurface. Moreover, it was shown that even for a worst case scenario potential methane accumulation in the basement of neighboring buildings are non-hazardous and well below the explosive limit of 5 vol-%.