Site-dependent fate assessment in LCA: transport of heavy metals in soil

In spite of many recent advances in the impact assessment of emissions to air, surface water, and upper-soil layers, methods for emissions to deep soil layers and the groundwater are still missing for assessment tools such as life-cycle assessment (LCA). The goal of this paper is to provide such a method for assessing the fate of heavy metals in soils. The method was developed for the emissions from slag landfills but could, in principle, also be used in other applications. Our guidelines serve to estimate the transport time needed for a heavy metal to reach the groundwater as a function of spatial parameters such as infiltration rate, macropore flow, pH value, content of organic material, and distance to the groundwater. Default values for these parameters are suggested for typical landfill sites in Switzerland. The application of the method is illustrated in three case studies of actual landfill sites in Switzerland. The results of these case studies indicate that the retardation of heavy metals varies greatly depending on the local properties of the soil considered. Moreover, it is illustrated how the suggested procedure can be integrated into existing multimedia-fate models used in LCA.