Shortterm transport of cadmium during a heavyrain event simulated by a dualcontinuum approach

The transport of solutes in soils, and its intensification due to preferential flow, plays crucial role when problems related to the groundwater pollution are dealt with. The objective of this study was to examine transport of cadmium Cd in response to an extreme rainfall event for three different soils using numerical modeling. The 115mCd2concentration profile had been measured in the Bodiky reference site Danubian Lowland, Slovakia by the radioactivetracer technique and used for the calibration of the dualcontinuum model S1D. The Cd transport during a single rain event was predicted with the S1D model for light, mediumheavy, and heavy soil in the same region. The Cd transport through the soil profile was simulated by the onedimensional dualpermeability model, which assumes the existence of two pore domains: the soilmatrix domain and the preferentialflow domain. The model is based on Richards equation for water flow and advectiondispersion equation for solute transport. A modified batch technique enables to distinguish process of adsorption in the matrix domain and the preferential pathways. Modeling with classical singlepermeability approach and dualcontinuum approach without considering the particlefacilitated transport led to negligible Cd penetration. The rainfall event with extremely high rainfall intensity induced deep penetration of Cd in the mediumheavy and heavy soil, which may indicate increased vulnerability to shallow groundwater pollution for the respective sites in Danubian Lowland region. The highest Cd leaching was predicted for heavy clay soil, where the preferential particlefacilitated transport of Cd through the soil profile was significant due to the contrasting properties of the soilmatrix domain and the preferentialflow domain. The results of the sensitivity analysis suggested only slight effect of the transfer rate coefficients on simulated Cd leaching.