Investigating Multispecies Reactive Transport in Porous Media: A Simulation and Moment Analysis Approach

Contaminant migration in subsurface environments critically threatens groundwater, particularly near chemical and nuclear repositories. This study employs both the Finite Difference Method (FDM) and COMSOL for two-dimensional multispecies reactive transport modeling in saturated porous media. The models simulate advection, dispersion, and first-order decay and are validated against analytical solutions with excellent accuracy. A key feature is the incorporation of three dispersivity scenarios of constant, linear, and exponential distance-dependent dispersivities which is applied to radionuclide (RN) decay chains and chlorinated solvents (CS). A novel contribution of this work is the comparative analysis of these dispersivity scenarios, revealing their influence on solute plume mobility and retardation factors. Significant differences in retardation factors for RN and CS highlight the applicability of the model across diverse environments. Spatial moment analysis demonstrates that the species with the largest plume may not dominate subsurface migration. The application of effective dispersivity in interpreting tracer breakthrough curves significantly improves numerical precision and field relevance. The integration of FDM and COMSOL allows for cross-validation of results, offering a robust and reliable framework for modeling reactive transport. This approach provides enhanced insights into the long-term environmental impacts of reactive contaminants and aids in the development of effective remediation strategies. By integrating these numerical methods, the study delivers a valuable insight to mitigate contamination risks in sensitive environments, with broad applicability for safeguarding groundwater near chemical and nuclear repositories.