Quantifying interactions between precipitation, surface water, groundwater and mine water using nonlinear multi-endmember mixing model: Case study in an open-pit coal mine of eastern Inner Mongolia, China

This study was conducted in an open-pit coal mine with high mine water inflow in eastern Inner Mongolia, China. Given the importance of interactions between precipitation, surface water, groundwater, and mine water (“four waters”) in protecting water resources, a nonlinear multi-endmember mixing model was developed and combined with field monitoring to quantify water fluxes and hydrochemical characteristics, reveal interaction processes and controlling mechanisms, and develop control and recharge strategies. This study provides novel hydrological insights into the interactions of four waters toward ecologically sustainable pathways in open-pit mining areas. In 2024, mine water was supplied by precipitation (0.16), surface water (0.29), and groundwater (0.55) —the dominant source —with 95 % confidence intervals of [0.09–0.23], [0.20–0.37], and [0.47–0.65], respectively. The main interaction pathway extended from precipitation to groundwater and subsequently to mine water, with groundwater contribution remaining stable despite interannual rainfall variability. Rainfall variability and the construction of cutoff curtains were identified as the primary drivers of interactions. Further analyses demonstrated that implementing cutoff curtains for inflow control and same-layer in-situ recharge for water supplementation optimized interaction pathways of four waters. These findings provide a framework for coordinating mine water management and human–water feedbacks, offering a reference for resource protection and rehabilitation in over 30 open-pit coal mines in eastern Inner Mongolia. • Developed and optimized an Integrating Nonlinear Multi-Endmember Mixing Model. • Integrated hydrochemistry, isotopes, and monitoring data into a unified analysis framework. • Provided a universal method that quantifies the interactions between the four waters. • Supported the development of a “control–storage–utilization” water management framework.