## 2 Materials and Methods
### Groundwater Numerical Simulation
#### 2.2.3 Groundwater Flow Numerical Model  
Based on the established hydrogeological conceptual and mathematical models of the mining area, a 3D hydrogeological model of the simulation area was developed using the MODFLOW module in the GMS software, utilizing the finite-difference calculation method. Figure 4: Geological conditions. After processing the borehole data, they were imported into the 3D groundwater numerical simulation software (GMS), resulting in the generation of the borehole distribution profile for the study area (Figure 5). Based on the borehole data, a geological model for the study area was established (Figure 6). Because this study focused on the Taiyuan Formation limestone and the adjacent aquifers had minimal influence on it, the simulation considered only the Taiyuan Formation limestone aquifer to enhance accuracy and relevance. * Hydrogeological Parameter Zoning  
The study area was divided into hydrogeological parameter zones based on the characteristics of the Taiyuan Formation limestone aquifer, the geological structure, and data from pumping tests. Each zone was defined to include at least one hydrogeological or observation well to ensure data reliability. The horizontal permeability coefficient for each zone was approximated using the permeability coefficient from the controlling hydrogeological or observation well. The northeastern part of the study area was divided into five zones, with the F22 fault delineating the boundary. Other zones were segmented based on the principle that at least one borehole should be present in each zone, which facilitated the preliminary setting of hydrogeological parameters (Figure 7). Figure 6: Geological model of study area. Figure 7: Schematic diagram of hydrogeological parameter zoning. Initial Head Setting  
The initial head in the simulation area was set using water levels from observation wells recorded on 30 May 2022, before the commencement of the drainage test. The initial flow field of the limestone water in the simulation area was generated using the Kriging interpolation method in simulation software. Groundwater flow in the limestone aquifer predominantly moves from north to south. In the initial flow field, the water head in the northeastern part of the mining area is relatively higher, owing to the uplift caused by the F22 fault. Compared to the southern part of the mining area, the hydraulic gradient in the northeast is smaller, resulting in more gradual water-level changes (Figure 8). Temporal Discretization  
The simulation period spanned one year, employing a monthly stress period division scheme. The entire simulation duration was divided into 12 stress periods, with each period corresponding to a calendar month, ranging from 28 to 31 d. This division approach better reflected the monthly variation characteristics of hydrological processes while maintaining consistency with actual conditions. To ensure that the established model accurately reflected the actual groundwater conditions, the model underwent calibration and validation. Based on changes in water discharge and observation well water levels during the dewatering process, the 12 stress periods were divided into two phases. The first phase, the calibration phase, spanned from 1 June 2022 to 31 August 2022, lasting 92 d and including three stress periods. The second phase, the validation phase, extended from 1 September 2022 to 1 June 2023, totaling 274 d and including nine stress periods. Model identification and validation ensured that the simulated water levels and their variation aligned with actual measurements. Additionally, dynamic changes in the simulated flow field had to correspond to observed trends, and the hydrogeological parameters derived from the model had to match real conditions. Figure 8: The initial head distribution of the aquifer. Note: the units of the labels in the figure are in meters (m).