Modelling Contaminant Transport in Anthropogenic Soil: Reconstruction of Spatial Heterogeneity by Analysing the Relations of Adjacent Pedofacies

Flow and transport of water and solutes in soil is controlled by both the structural heterogeneity of the physicochemical soil parameters and the temporal variability of boundary conditions and driving gradients. We will present an approach for the modelling of contaminant transport at highly contaminated industrial sites. Special consideration is put on the reconstruction and mapping of the spatial heterogeneity of adjacent pedofacies with highly contrasting properties. Employing a thorough field survey, we will provide evidence that urban and industrial sites are characterized by a spatial heterogeneity of contaminant sources and sinks which is neither solely random nor regular in nature. To reconstruct the spatial heterogeneity of such sites we applied a conditional stochastic simulation based on the Markov process theory. Markov processes facilitate the reconstruction of spatial random numbers by which the local state solely depends on the direct neighbour and not on more distant occurrences. By doing so we adequately reconstructed both the pedofacies and the contamination levels observed. With a finite and relatively small number of combinations of pedofacies and contamination levels we were able to cover more than 60 % of the spatial heterogeneity of the site. The typical soil profiles were then used with a process-based reactive transport model in order to assess the risk of groundwater contamination. The proposed procedure is a compact, yet mathematically simple and comprehensive approach to a riskbased assessment of soil and groundwater pollution by hazardous substances found at anthropogenic sites of urban and industrial environments.