Unraveling two-dimensional modeling of multispecies reactive transport in porous media with variable dispersivity

Abstract

The movement of reactive contaminants in subsurface has led to variations in groundwater quality, particularly near chemical and nuclear repositories because of the geochemical and hydrodynamic processes involved in porous media. This study deals with the two-dimensional numerical model to address multispecies transport through saturated porous media with steady-state flow conditions, considering advection, longitudinal and transverse dispersion with the first-order decay and the same is validated with the analytical solution. Focusing on four-species radionuclide decay, this study explores three dispersion models considering constant (ADC), linear (ADL) and exponential distance-dependent dispersivities (ADED) and their comparative analysis reveals the plume mobility emphasizing the role of dispersivity in shaping reactive solute transport by incorporating effective dispersivity. The results show that the concentrations of all radionuclides exhibit their peak values within the source area at time of 500 years, in which ²²⁶Ra has the largest plume and a discernible decrease of 12% and 20% is observed in the first moment for ADL and ADED as compared to ADC. Also, the relative plume size is in the order of ²²⁶Ra > ²³⁸Pu > ²³⁴U > ²³⁰Th stipulating that the daughter species with largest plume may not necessarily dominate migration. Further, the spatial moments are used to encapsulate the sensitivity analysis, extending the applicability to simulate reactive transport scenarios. This study enhances the ability to predict and understand the long-term environmental perturbations by developing methodologies for modeling and forecasting the contaminants behavior that contributes to SDG-6 and SDG-13 through sustainable groundwater management.