Experimental Insights into Cadmium Transport in a Heterogeneous Saturated Subsurface Using a Two-Dimensional Tank

Cadmium (Cd) is a priority groundwater contaminant of significant environmental concern, as its presence in subsurface water systems poses serious risks to both human and ecosystem health. A better understanding of cadmium transport under heterogeneous subsurface conditions representative of real aquifers is essential for accurately predicting its fate and for designing effective remediation strategies. This study investigates cadmium transport in saturated heterogeneous subsurface using a two-dimensional laboratory tank packed with an undisturbed soil core to generate high-quality experimental data under realistic flow regimes. Initially, a conservative tracer test using sodium chloride (NaCl) was conducted to assess flow dynamics, hydraulic connectivity, and preferential flow pathways within the heterogeneous medium system. The tracer results confirmed non-uniform flow behaviour and significantly reduced pore-water velocities due to the low permeability and structural heterogeneity of the undisturbed soil. After achieving steady-state flow conditions, a cadmium transport experiment was performed by introducing a 1000 ppb Cd solution under constant hydraulic conditions.  Water samples were collected at selected time intervals and analysed using inductively coupled plasma mass spectrometry (ICP-MS) to quantify cadmium concentrations. The experimental results reveal delayed cadmium breakthrough and pronounced tailing behaviour, highlighting the dominant influence of heterogeneity, reduced hydraulic conductivity, and enhanced sorption processes on cadmium transport dynamics in natural subsurface systems. The dataset generated provides a robust foundation for calibrating and validating reactive transport modelling under heterogeneous conditions. This experimental framework supports science-based groundwater quality management and informed decision-making in contaminated aquifers.