## 3 Research on Water-Inrush Sources
### Chemical Analysis of Water Inflow in the Working Face  
In this study, during the exploration period, water samples were collected from the Changxing Formation aquifer, surface water sources, and other locations and then subjected to comprehensive water quality analysis. Furthermore, following water-inrush incidents at the working face, additional samples were collected and sent to qualified third-party water quality testing institutions for comprehensive analysis (Table 2), thus ensuring the accuracy of water quality assessments. Analysis of surface streams and rivers within the mining area indicated that water near the exposed limestone of the Changxing Formation primarily comprised HCO\({}_{3}\)-SO\({}_{4}\)-Na-type water, with a total dissolved solids content of 515.50 mg/L-907.50 mg/L. Limestone water from the Changxing Formation (sampled at elevation 794.7 m-883.83 m, with burial depth of 333.42 m-409.30 m) was mainly composed of HCO\({}_{3}\)-SO\({}_{4}\)-Na (Na+K)-Ca, HCO\({}_{3}\)-SO\({}_{4}\)-Ca-Na (Na+K)-type water, with a total dissolved solids content of 168.00 mg/L-279.50 mg/L. After water inrush on the roof of the working face in the coal mines, a sample (collected at an elevation of 776 m-985 m and buried depth of 172 m-450 m) was subjected to comprehensive analysis, revealing water quality types characterized by HCO\({}_{3}\)-Na and HCO\({}_{3}\)-SO\({}_{4}\)-Na, with a total dissolved solids content of 327.76 mg/L-892.59 mg/L. Given the data in Table 2, a Piper diagram of the hydrochemical properties of surface water, Changxing Formation limestone water, and water outlet points was drawn according to the Shukarev hydrochemical types [26, 27, 28] (Figure 5). According to the Piper plot, surface water was generally located in low-lying areas and eventually flowed into rivers. The water quality was significantly affected by residential activities, correlating with the relevant research by [PERSON] and [PERSON] [29]. Upstream areas of the river were mainly supplied by spring water, exhibiting higher Ca\({}^{2+}\) and Mg\({}^{2+}\) contents, accounting for over 70% of the cation composition. However, downstream, especially after passing through residential areas, the proportion of sodium ions gradually increased due to increased domestic sewage discharge, and the Na\({}^{+}\) and K\({}^{+}\) content gradually increased from ~27% to over 85%. Analysis of the on-site water intake locations indicated that water sample 3 was collected near the source of the river, which was replenished by limestone spring water in the Yulong Mountain section, exhibiting the highest concentration of Ca\({}^{2+}\) cations. Water sample 1 was collected from the Changxing Formation outcrop, situated in low-lying terrain and a residential gathering area, with Na\({}^{+}\) dominating the cation composition. Water sample 2 was collected from the limestone formation outcrop in the Yulong Mountain section, indicating a diluted river water composition due to limestone water inrush, resulting in lower Na\({}^{+}\) content and higher Ca\({}^{2+}\) content. In this study, before being affected by mining damage, the limestone in the Changxing Formation originally experienced slow or even stagnant groundwater flow (hydraulic conductivity 0.0000026 m/d-0.004 m/d) due to undeveloped karst. However, it also experienced relatively fast groundwater flow (hydraulic conductivity of ~0.1079 m/d) in locally developed karst areas. This change altered the water quality type of the limestone in the Changxing Formation from HCO\({}_{3}\)-SO\({}_{4}\)-Ca water to HCO\({}_{3}\)-SO\({}_{4}\)-Ca\(\cdot\)Na water, which  
Figure 5: Piper three-line diagram of surface water, karst water, and mine water. eventually became HCO\({}_{3}\)-SO\({}_{4}\)-Na-Ca water. The diversity of water quality types in the limestone water of the Changxing Formation indicated that under closed conditions, it primarily comprised HCO\({}_{3}\)-SO\({}_{4}\)-Ca.