Effects of coal mining on the evolution of groundwater hydrogeochemistry

Qiao, Wei; Li, Wenping; Zhang, Shengcai; Niu, Yunfei

Effects of coal mining on the evolution of groundwater hydrogeochemistry | Effet de l’exploitation des mines de charbon sur l’évolution de l’hydrogéochimie des eaux souterraines Efectos de la minería del carbón en la evolución de la hidrogeoquímica del agua subterránea 采煤对地下水水文地球化学演化的影响 Efeitos da mineração de carvão na evolução da hidrogeoquímica de águas subterrâneas

2019

Qiao, Wei | Li, Wenping | Zhang, Shengcai | Niu, Yunfei

The mining industry, especially coal mining, may severely affect the spatial and temporal evolution of groundwater. To provide a potential model outlining the hydrogeochemical evolution of groundwater as influenced by coal mining, a multi-layer groundwater system in a coal mining area was investigated. A total of 76 groundwater samples were collected between 1964 and 2018 for hydrogeochemical analysis from boreholes, underground tunnels, and surface pits at Xinglongzhuang Coal Mine in China. Hierarchical cluster analysis and principal component analysis were used to classify four significant groundwater zones and two principal components. The results showed that mining may have caused the rock strata to sink, obstructing the path linking the Permian and lower Quaternary aquifers, and resulting in intensified ion exchange in the lower Quaternary aquifer. The concentrations of Na⁺ and Ca²⁺ in the groundwater from the lower Quaternary aquifer changed over the studied period (~54 years). The gradual increase of Na⁺ and decrease of Ca²⁺ concentration verified the action of cation exchange. The four main aquifers had relatively independent hydrogeochemistry, suggesting that the hydraulic conductivity of the natural faults is weak and the sealing properties of hydrogeological drill holes in the coal field are good. Analysis of 26 heavy metals in the mine drainage water showed that there is only minor pollution after the water has been simply treated. These data analysis methods and results could be useful in areas with long-term mining to interpret the evolution of groundwater and to promote groundwater quality management.

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