Engineering Hydrogeology Research Related to Mining Activities

1. Introduction

The sustainable management of groundwater resources and the mitigation of hydrogeological risks in mining activities have emerged as critical challenges in environmental and geological engineering. Mining operations, particularly in deep coal seams and coastal areas, often intersect with complex hydrogeological systems, posing risks of water inrush, groundwater contamination, and ecological disruption [1,2]. Concurrently, the treatment of mining-induced wastewater and the reuse of solid wastes derived from dewatering processes present opportunities for sustainable development [3,4].

This Special Issue, “Engineering Hydrogeology Research Related to Mining Activities,” compiles ten contributions that address these challenges through interdisciplinary research. The studies span the numerical modeling of fault zone vulnerabilities, innovative water treatment technologies, and the resource recycling of mining by-products. Collectively, they advance the understanding of hydrogeological processes and propose practical solutions for risk mitigation and environmental protection.

2. Advances in Hydrogeological Risk Assessment and Water Treatment

2.1. Numerical Simulation and Risk Evaluation of Water Inrush

Several contributions focus on the dynamic evaluation of water inrush risks in coal mine floors, particularly in fault zones and graben structures. For example, Tian et al. (contribution 1) employ a fuzzy C-means clustering method to improve the vulnerability assessment of floor water inrush, integrating multi-factor analysis to refine risk zoning. This approach overcomes the limitations of traditional water inrush coefficient methods by incorporating geological structure complexity and aquifer properties. Lyv et al. investigate the impact of high-intensity coal mining on groundwater in the arid and semi-arid Ordos Basin, using the New Shanghai No. 1 Coal Mine as a case study. A large-scale pumping test was conducted to characterize the hydrogeological properties of the Baotashan sandstone aquifer, which poses significant water inrush risks due to its high-pressure storage below the coal seam floor. A three-dimensional numerical groundwater model was developed to simulate drainage dynamics and predict dewatering volumes under safe mining conditions [5]. The study provides a quantitative evaluation of mining-induced groundwater loss, offering scientific support for risk mitigation and water resource management in ecologically vulnerable mining areas.

Ma et al. employ EWMA-modified grey models optimized by particle swarm optimization to predict water inflow from faults (WIF), using data from the Buliangou Coal Mine [6]. The results demonstrate that the optimized REGM model significantly improves prediction accuracy, addressing the limitations of traditional grey models through enhanced time-series analysis and parameter optimization.

Angélica Geovanna Zea Cobos et al. (contribution 2) utilize numerical simulation to analyze the time-dependent mechanical response of fault zones under mining-induced disturbances. The study reveals that the duration and intensity of mining-induced stress significantly influence the initiation and propagation of plastic deformation, as well as the evolution of seepage fields. These findings underscore the critical role of mining sequence optimization in mitigating the risk of fault-controlled water inrush. Similarly, Ding et al. (contribution 3) adopt a coupled fluid–structure interaction (FSI) model to simulate the dynamic evolution of seepage fields in graben fault systems. Their results provide valuable insights into the mechanism of delayed water inrush triggered by progressive fault activation and stress redistribution, offering theoretical support for water hazard prevention in structurally complex mining areas.

Miao et al. (contribution 7) systematically analyze the technical characteristics of magnetic-source transient electromagnetic (TEM) coil devices for hydrogeological surveys in mining areas. The study categorizes TEM systems into fixed-source and moving-source types, and evaluates their performance in detecting water-rich zones and fault structures under varying geological conditions. The results provide practical guidance for selecting optimal TEM configurations, improving subsurface water detection and the risk assessment of water inrush.

In addition, Fan et al. further develop a roadway–borehole TEM method with a dynamic source and fixed reception setup. The approach combines geophysical detection with drilling techniques, enabling the accurate imaging of goafs and improving the identification of potential inrush hazards. Field validation demonstrates its effectiveness in complex underground environments [7].

2.2. Innovative Technologies for Groundwater and Wastewater Treatment

Environmental engineering solutions for mining wastewater are addressed in several studies. Yang et al. (contribution 4) investigate the use of Moringa oleifera as a natural coagulant to reduce turbidity in mining effluents, demonstrating its effectiveness in removing suspended solids and heavy metals. This sustainable approach offers a cost-effective alternative to chemical coagulants, particularly in regions with limited access to industrial chemicals.

Zhu et al. (contribution 5) present a multi-factor prediction model for mine water inflow, integrating residual networks, gated recurrent units, and a multi-head attention mechanism. The model improves prediction accuracy by incorporating microseismic energy and borehole water level data, enabling the real-time monitoring and early warning of water inrush. This data-driven approach showcases the potential of artificial intelligence in hydrogeological risk management.

Wang et al. employ transient electromagnetic surveys, electrical resistivity tomography, and self-potential methods to detect water-rich zones and seepage pathways in the Xiaogangou Coal Mine, demonstrating the effectiveness of integrated geophysical approaches in delineating aquifers and identifying infiltration channels [8]. The study highlights the role of surface river recharge through fractured rock and sandstone layers, offering a practical solution for groundwater hazard assessment in complex geological settings.

Hao et al. develop an advanced ozone oxidation process to treat copper mine wastewater, effectively reducing residual manganese concentrations from 20–100 mg/L to below 2 mg/L [9]. This sustainable method outperforms traditional potassium ferrate oxidation in both efficiency and cost, offering a practical solution for manganese removal in acidic, metal-rich effluents.

Moreover, Madzin et al. optimize biochar derived from spent mushroom compost (SMC) for removing heavy metals (Cu, Mn, Fe, and Pb) from abandoned mine water, demonstrating its effectiveness varies with pyrolysis temperature. The biochar produced at 500 °C shows the highest adsorption capacities, with removal performance influenced by pH and initial metal concentrations. Adsorption follows Langmuir and pseudo-second-order kinetics, driven by cation exchange, electrostatic interaction, and π-complexation [10]. This study highlights SMC biochar as a sustainable, cost-effective alternative to activated carbon for heavy metal remediation in mine water treatment.

2.3. Sustainable Utilization of Mining By-Products

The resource recycling of mining wastes is explored in Yu et al. (contribution 6), which focuses on dewatering sludge. Contribution 6 develops a reinforcement grouting material using dewatered sludge, demonstrating its feasibility for stabilizing heavy metals (e.g., Cr and Ni) and improving mechanical properties. This approach not only mitigates environmental pollution but also reduces the demand for traditional construction materials.

Moreover, Antunes et al. evaluate the feasibility of incorporating natural mining by-products into stabilized rammed earth (SRE) construction materials. Three mixtures—pure clayey soil, clayey soil with mining by-products, and pure mining by-products—are tested with varying cement contents (2.5% and 5%) [11]. The results show that adding mining by-products significantly improves the unconfined compressive strength (UCS), especially in stabilized samples. While unstabilized samples fail in water exposure, mixtures with mining by-products retain structural integrity. The M3C5 mix meets the standards for soaked UCS and durability, demonstrating the promising potential of mining by-products in sustainable earth construction.

The valorization of industrial by-products is explored in Sánchez et al., which investigates the use of coal fly ash and steelmaking slag as soil amendments for the remediation of highly As- and Hg-contaminated mining soils [12]. The study combines these by-products with Betula pubescens phytoremediation and an organic fertilizer to evaluate their effects on pollutant immobilization, plant physiology, and leachate treatment. The results show that the by-products significantly reduce the availability and leaching of As and Hg, enhance plant growth, and promote the retention of Hg as stable compounds. This approach highlights the potential of integrating waste recycling and phytoremediation for sustainable soil restoration in contaminated mining areas.

In addition, Fadila et al. investigate the reuse of mining by-product Porcellanite as a thermal energy storage (TES) material for recovering industrial waste heat in Moroccan mining operations. The study integrates a thermocline packed-bed system using thermal oil as the heat transfer fluid and demonstrates favorable thermophysical, mechanical, and durability properties of the by-product after thermal cycling. Numerical simulations show high charge (87%) and discharge (88%) efficiencies, and economic analysis confirms the viability of the system, supporting the potential of mining waste in circular economy applications [13].

3. Multidisciplinary Approaches to Groundwater Management

The contributions in this Special Issue exemplify the integration of geological engineering, environmental science, and data analytics. For instance, Huang et al. (contribution 8) combine field monitoring with numerical modeling to assess the impact of coastal aquifer mining on groundwater chemistry, highlighting the role of seawater intrusion and land use change. This interdisciplinary approach is crucial for addressing the compounded risks of saltwater contamination in coastal mining regions.

Xu et al. (contribution 9) investigate the stabilization/solidification (S/S) of municipal sludge using alkali-activated coal gangue-slag binders, demonstrating the synergistic effects of material composition and curing conditions on heavy metal immobilization. The study bridges materials science with environmental engineering, offering a sustainable solution for sludge treatment in mining-affected areas.

Ju et al. (contribution 10) explore the use of transient electromagnetic methods with conical field source coils to improve the resolution of shallow groundwater detection. This technological innovation enhances the accuracy of hydrogeological mapping, particularly in complex strata where traditional methods may underperform. Furthermore, Cao et al. investigate the coupled impact of thick-hard magmatic roofs and confined aquifers on floor failure mechanisms and water inrush evolution during coal seam mining. By integrating plastic theory, numerical simulation, BP neural network prediction, and field validation, the study reveals how mining-induced stress redistributions and roof–-floor interactions intensify floor deformation, crack propagation, and water-conducting channel formation [14]. This multidisciplinary approach enhances our understanding of floor failure modes and supports risk mitigation in complex hydrogeological settings.

Huang et al. explore sustainable groundwater management in the Pearl River Delta, where rapid urbanization and seawater intrusion pose increasing threats to water security. By integrating machine learning and knowledge-driven models, the study maps groundwater potential and assesses vulnerability. LightGBM outperforms other algorithms in identifying high-potential zones, while GALDIT effectively captures seawater intrusion risk. The analysis highlights the influence of geomorphology, land surface temperature, and human activities [15]. The proposed strategies, including extraction planning and pollution control, offer a data-driven framework for groundwater governance in complex coastal settings.

Additionally, Zeng et al. propose a double verification and quantitative traceability (DV-QT) method to improve the accuracy of identifying mixed mine water sources, addressing the limitations of conventional hydrochemical and groundwater-level-based approaches. By integrating consistency checks, inrush channel validation, and multivariate mixing calculations, the method enhances interpretability and enables quantitative source attribution, offering a practical solution for complex hydrogeological settings [16].

4. Conclusions

The studies compiled in this Special Issue advance the frontiers of hydrogeological risk assessment and sustainable water management in mining and environmental engineering. Key insights include the following:

The integration of fuzzy clustering, neural networks, and machine learning enhances the precision of water inrush risk zoning and floor failure prediction, outperforming traditional empirical approaches. Numerical simulations incorporating plastic zone theory and stress–seepage coupling deepen the understanding of delayed water inrush and catastrophic failure mechanisms under conditions such as thick-hard roofs, thin aquifers, and isolated coal pillars. Natural coagulants and alkali-activated materials offer sustainable solutions for wastewater treatment and solid waste recycling, contributing to reduced environmental impacts. Innovations such as transient electromagnetic detection and GIS-integrated evaluation methods improve the resolution of subsurface water mapping and enhance the control of confined aquifer hazards. Furthermore, the development of double verification and quantitative traceability techniques significantly improves the accuracy of mine water source identification, particularly in mixed-source and complex hydrogeological settings.

Future research should focus on scaling these technologies for industrial application, integrating real-time monitoring systems with predictive models, and addressing the cumulative impacts of climate change on hydrogeological systems. The multidisciplinary approaches presented here lay a solid foundation for sustainable mining practices that balance resource extraction with environmental stewardship.