Abstract : Many previous studies showed that the classical advection-dispersion equation (ADE) is not capable to well simulating solutes transport in the heterogeneous field soil and it does not take into consideration the speciation of the solutes in the geochemical soil system. In this thesis, new fractional hydro-geochemical model was proposed for simulating the transport and speciation of heavy metals in the unsaturated soil zone at the steady- unsteady state. This model was proposed for overcoming the limitations of the classical advection- dispersion model (ADE). At the steady state, the analytical solution of the fractional advection dispersion model (FADE) was coupled by MATLAB code with the geochemical reactions model and the new model was validated with experimental data. At the unsteady state, new numerical solution of FADE was proposed and coupled with the water flow model and the geochemical model. MATLAB code was written for the new model and the well known transport models HYDRUS-1D and HP1 were used for testing the applicability of the new model.
The validation results showed that the new fractional hydro-geochemical model well simulates the transfer of solutes in the unsaturated soil zone and it is capable to giving more details about the forms (species) of the solutes in the geochemical soil system. The new model was used for studying the transfer of zinc in the Kempen region (in the border between Belgium and the Netherlands); this region is heavily polluted by heavy metals emitted from the zinc smelters existing in the region. Then, a sensitivity analysis was made for determining the sensitivity of the new model for the hydrological and geochemical parameters. Soil hydraulic conductivity (Ks), saturated soil water content (θs) and initial soil water content (θini) are the most affecting factor for the water flow model. The fractional solute transport model was sensitive to the values of the fractional order (α) and the dispersion coefficient (D). pH value is the most affecting geochemical factors followed by the concentration of SO42- ,Cl- and CO32 - . There was no significant effect of the other cations ( Al 3+ ,Mn 2+ ,Fe 2+ ).