Thermally driven organic contaminant migration in soil-groundwater systems: field-scale modeling with temperature...

The migration of organic pollutants in soil-groundwater systems involves complex coupled thermal and hydrodynamic processes as well as multiphase interactions, all of which are highly sensitive to thermodynamic conditions. Conventional contaminant transport models often neglect near-surface and subsurface temperature gradients, thereby limiting their ability to reproduce observed migration behavior under field conditions. To address this gap, this study developed a coupled thermal-hydrodynamic field model to simulate the multiphase partitioning and spatial evolution of chlorobenzene under non-isothermal conditions at an organically contaminated site. The results show that the spatiotemporal variability of the subsurface temperature field substantially influences the multiphase partitioning and migration dynamics of chlorobenzene. The temperature field regulates key thermodynamic parameters, including saturated vapor pressure, Henry's law constant, and aqueous solubility, thereby controlling chlorobenzene volatilization, dissolution, and phase transitions. Comparative simulations between isothermal assumptions and the temperature-field-coupled model revealed distinct differences in migration patterns. Chlorobenzene migration exhibited marked seasonal variability: lateral spreading intensified from spring to autumn in response to warming, whereas winter cooling significantly constrained plume expansion. This temperature-coupled behavior provided a closer match to observed spatiotemporal contamination patterns than the isothermal simulations. At the microscale, temperature affects contaminant transport by regulating key physicochemical parameters, thereby modulating convective-diffusive transport, volatilization, dissolution, multiphase partitioning, and the spatial fate of organic pollutants. Overall, this study highlights the limitations of conventional isothermal models in representing temperature-sensitive migration processes for risk assessment and remediation design. The developed multi-field coupled model reduces simulation errors and provides a reliable framework for reproducing observed pollutant migration behavior under realistic climatic conditions. This framework can support the design of seasonally adaptive containment and treatment strategies, the optimization of long-term monitoring networks, and more efficient resource allocation at contaminated sites.