Numerical simulation evaluation of lithium leachate from landfills and risk to shallow groundwater

Study regions: Southeast inland region of China. Study focus: The disposal of lithium slag, a byproduct of lithium-ion battery manufacturing, presents environmental risks by altering groundwater flow and contaminant transport. Because hydrogeological conditions are complex, reliable numerical models are needed to forecast changes in groundwater flow due to landfill fills and delineate long-term diffusion pathways. This study evaluates the hydrogeological impacts of landfilling native soil and lithium slag–soil mixtures at 6:4, 7:3, and 8:2 ratios using groundwater-modeling simulations. By incorporating uncertainties in hydraulic conductivity, dispersion, adsorption, and reaction rates, we identify robust monitoring strategies under worst-case scenarios. New hydrological insights for the region: Field-calibrated simulations show landform changes and recharge variations accelerate contaminant migration by advection and dispersion. A groundwater-table rise of 2–4 m within 3–5 years raises contamination risk, especially in unlined landfills. With parameter uncertainty, native-soil plumes can extend up to 1700 m westward in 20 years. The 8:2 slag–soil mixture with a clay cap most effectively reduces leakage by more than 30 %. Entropy-based analysis identifies two high-sensitivity zones for early detection and guides monitoring-well placement. Engineered barriers are crucial to mitigating long-term groundwater contamination from lithium-rich waste. The findings provide technical guidance for preventing pollution at landfill sites under rising groundwater. These insights support risk-based remediation planning and monitoring design for landfill sites facing rising groundwater, and inform policy decisions.