Microplastic Transport in Groundwater Systems: An Integrated Field, Laboratory, and Numerical Modelling Study

Microplastics have emerged as contaminants of concern in groundwater systems, yet their transport behaviour and fate in subsurface environments remain insufficiently understood. This thesis investigates microplastic occurrence and transport in groundwater through an integrated approach combining field observations, laboratory experiments, and numerical modelling. Field sampling was conducted across Chennai's aquifer systems during pre-monsoon and post-monsoon periods . Microplastics were detected at all sampling locations, with concentrations increasing between campaigns . Sandy formations showed higher concentrations compared to clayey zones . Fibres dominated the morphological assemblage, with polyvinyl chloride, polyethylene, and polypropylene as the most frequently identified polymers . Laboratory column experiments investigated transport behaviour across four sand grain sizes spanning fine to coarse fractions . Fine and medium sand exhibited delayed breakthrough with substantial hydraulic conductivity reductions, while coarse sand demonstrated early breakthrough with minimal hydraulic impact. Physical straining was identified as the primary retention mechanism, with particle-to-pore-throat size ratios serving as a controlling parameter . A numerical model incorporating advection-dispersion equations with retention terms for attachment, detachment, and straining reproduced experimental patterns with strong agreement between predicted and observed breakthrough curves . The model accounted for porosity and permeability evolution during particle accumulation .The findings indicate that grain size distribution governs both microplastic transport efficiency and hydraulic consequences in porous media . The convergence of field, laboratory, and modelling results supports the identified transport mechanisms and provides a basis for assessing aquifer vulnerability to microplastic contamination.