Modelling water intrusion impacts on pollutant transport from a municipal solid waste landfill in Sweden

Sammanfattning: The landfills located at the sea shore or below the ground water table are a severe cause of concern due to their close proximity to sensitive coastal ecosystems and pristine ground waters. Therefore, it is important to assess the long term environmental risks of coastal landfills before their final closure. In this context, the reactive transport models, by allowing us to study the complex interplay of leachate, estuarine and ground waters, can help us in predicting the long-term impacts of these sites. The present study attempted to model the impact of sea and ground water intrusion on leachate quality and migration at the onset of final closure of the Spillepeng landfill in Malmö, in southern Sweden. This objective was achieved by using a reactive transport code called PHREEQC. For transport modelling, different scenarios were considered; 1) Ground water and seawater flooding the landfill at the onset of final closure period, 2) The leachate migrating from the landfill in the long run, and 3) a worst case scenario was considered by increasing the hydraulic conductivity as a result of changes in porosity of the landfill barrier. Within these scenarios, the processes like solute transport, cation exchange and degradation of DOC were modelled. The modelling results showed that the seawater can breakthrough the landfill through the barriers within 100 years. The diffusion dominated transport, significantly increased this time span. Even after the 500 years the seawater could reach up to 8 meters in the barrier. The simulation of reactive processes showed that Na was replacing Ca from exchanges sites in the barrier. This raised possibility of sealing of pores and reduction in hydraulic conductivity due to dispersion. The modelling of biodegradation reaction for DOC in leachate showed the depletion of redox buffer in bottom sediments close to landfill. It was concluded that due to low concentrations of pollutants, dilution, and attenuation from biodegradation Spillepeng was not a serious long term threat to both coastal and ground waters. Finally, it was suggested that the assessment of that problems due to extreme events such as storms, sea level rise, and tidal fluctuations should be incorporated in future studies.