Background Open-pit coal mines in China are primarily distributed in arid and semi-arid regions such as Xinjiang and Inner Mongolia. However, the contradiction between coal mining and groundwater resource conservation is increasingly prominent in these regions. Specifically, a substantial amount of mine water inflow produced during coal mining tends to lead to the further loss of groundwater resources within the influence range of a mining area. Concurrently, the failure of efficient mine water storage intensifies the regional water shortage.

Methods This study investigated a typical open-pit coal mine in eastern Inner Mongolia. Using methods such as field survey and sampling, borehole monitoring, laboratory hydrochemical tests, and numerical simulation, this study primarily determined the quantitative composition, hydrogeochemical characteristics, and mutual conversion relationships of meteoric water, surface water, groundwater, and mine water (collectively referred to as the four water resources). Furthermore, this study established a three-dimensional storage and comprehensive allocation and utilization system for the four water resources in the open-pit mining area.

Results and Conclusions  The results indicate that the groundwater and mine water in the mining area were primarily recharged by meteoric water. Under the influence of open-pit coal mining, the regional groundwater loss reached 3 081.2×10⁴ m³/a, leading to the formation of a groundwater depression cone with an average area of 15.26 km² and a radius of approximately 1.88 km. Given the scarce meteoric water and intense evaporation in the area, the total groundwater loss in the mining area could exceed 40×10⁸ m³/a. Accordingly, this study proposed a three-dimensional mine water storage framework, which involved five modes: surface storage, storage on the pit bottom and slopes, the reconstruction of ecological aquifers in the waste dump, water reinjection into the Quaternary loose aquifer, and water reinjection into the deep bedrock aquifer in the coal seam floor. By combining the water quality and quantity characteristics of the four water resources and the water demand of various water consumption sectors, this study proposed five water allocation and utilization pathways: production and ecological water use within the mining area, as well as domestic, industrial, agricultural, and ecological water use in surrounding areas. By constructing an allocation model for the four water resources using an improved genetic algorithm, this study established a three-dimensional storage and comprehensive allocation and utilization system characterized by four water resources, five storage modes, and five utilization pathways for the open-pit mining area. Combining the calculation results of the allocation model of the four water resources, this study developed a groundwater resource conservation philosophy for the mining area, which utilizes groundwater drained from mines as the water source, centers on water reinjection (365×10⁴ m³/a) into the Quaternary aquifer outside the grouting curtain used to cut off water on the east slope, and stores water (20×10⁴ m³) dynamically on the pit bottom and slopes. Simulation results indicate that the maximum rise in the groundwater table of the Quaternary aquifer outside the grouting curtain reached 1.54 m. This finding indicates that the philosophy can effectively reduce groundwater loss caused by open-pit coal mining and facilitate regional groundwater table rise. The results of this study hold significant theoretical implications and considerable engineering application value for the efficient storage, conservation, allocation, and utilization of open-pit mine water.