Hydrochemical characteristics and quality assessment of groundwater in typical coal mining areas of Fuyuan, eastern Yunnan

This paper is the result of hydrogeological survey engineering.

Objective Fuyuan County, in eastern Yunnan, is an important coal producing area in southwest China. Understanding the hydrochemical characteristics, evolution and water quality of groundwater is of great significance for the protection and utilization of water resources in this area.

Methods This paper takes the typical coal mining area of Fuyuan County in eastern Yunnan as the main object. We systematically collected 97 water samples and analyzed the data using Piper diagram, Gibbs diagram, factor analysis, and ion ratio coefficients to identify the groundwater chemical characteristics and influencing factors in the study area. The groundwater quality was evaluated by the fuzzy comprehensive evaluation method.

Results The average pH value of the groundwater in the study area is 7.58, which is weakly alkaline. Total hardness (TH) value ranges from 22 to 1192 mg/L, averaging 208.28 mg/L. The value of total dissolved solids (TDS) ranges from 44 to 2322 mg/L, averaging 347.60 mg/L. The cations are mainly Ca²⁺ and Mg²⁺, and the anions are mainly HCO₃⁻. The hydrochemical types are HCO₃−Ca and HCO₃−Ca·Mg. The mine water is enriched in Na⁺ and SO₄²⁻, and the hydrochemical type is SO₄−Ca and HCO₃−Na.

Conclusions The groundwater chemistry composition in the study area is mainly affected by rock weathering leaching, cation exchange, and human activities. Human activities, as the overall driving factor, include specific sources such as domestic sewage, agricultural activities, and mining activities. Ca²⁺, Mg²⁺, and HCO₃⁻ are mainly derived from the dissolution of carbonate and silicate. Na⁺ and SO₄²⁻ are mainly influenced by mining activities, with cation exchange and oxidation of sulphides in coal beds as their main ionic sources. K⁺, Cl⁻ and NO₃⁻ are mainly affected by domestic sewage and agricultural activities. APCS-MLR analysis further shows that the groundwater chemistry composition mainly includes five sources: sulfuric-acid-involved dissolution of carbonate rocks, dissolution of silicate rocks and cation exchange, domestic sewage, agricultural activities, and unknown sources, and their contribution rates to groundwater are 35.01%, 19.39%, 11.97%, 22.47%, and 11.17%, respectively. It indicates that human activities are the main driving factors of the groundwater chemistry in the study area. In conclusion, the regional groundwater quality is generally good, with Grades Ⅳ and Ⅴ groundwater mainly distributed in clastic rock areas with frequent mining activities. The groundwater quality is affected by coal mining activities to some extent.