Formation And Controlling Factors Of Hydrochemical Composition For A Multilayer Aquifer System In The Yuaner Coal Mine

The hydrogeological conditions of Yuaner coal mine are extremely complex.The main water-filled aquifers include the confined loose layer pore fourth aquifer（referred to as the"the Fourth aquifer"）,the Permian coal measure sandstone fissure aquifer（referred to as the"the coal measure aquifer"）and the Taiyuan limestone karst fissure aquifer（referred to as the"the Taihui aquifer"）.Coal mining activities have changed the hydrogeological conditions of multilayer aquifer system,and caused a series of mine water environmental problems in the mining area.It is an important premise that investigating the hydrochemical characteristics,the formation of hydrochemical composition and control factors of groundwater system to determine the hydrogeological conditions and protect groundwater resources in mining area.To reveal the formation of hydrochemical composition and control factors in the study area.In this paper,50 water samples from the main water-filled aquifers of Yuaner coal mine were selected.The hydrochemical characteristics are analyzed by means of mathematical statistics of groundwater chemistry,Piper diagram and the relationship between main ions and TDS.Gibbs diagram,saturation index analysis,ion proportion coefficient method and principal component analysis are used to study the formation of hydrochemical composition.It reveals the controlling factors of the formation of hydrochemical components combined with rock minerals,geological structure,hydraulic connection and human activities.in the study area.Finally,quantitative verification is carried out by hydrogeochemical inverse simulation.The results show that:（1）The main water-filled aquifers in the mining area are weakly alkaline,and compared with the Fourth aquifer and Taihui aquifer,the variation coefficient of main ions in coal measure aquifer is larger.The main influence ions of TDS is Cl^-in the Fourth aquifer,and the main influence ions of TDS are Na⁺and Cl^-in the coal measure aquifer and the Taihui aquifer.The hydrochemical types of the Fourth aquifer are mainly HCO₃-Na,HCO₃·Cl-Na,Cl·HCO₃-Na,and Cl-Na.The hydrochemical types of the coal measure aquifer are mainly HCO₃-Na,HCO₃·Cl-Na,and Cl·HCO₃-Na.The hydrochemical types of the Taihui aquifer are mainly Cl·HCO₃-Na,HCO₃-Na,Cl-Na,HCO₃-Na·Ca,and HCO₃·Cl-Na.（2）The chemical composition of groundwater in the study area is mainly controlled by water rock interaction.The dissolution state of aquifer minerals is different in space.The formation of the main hydrochemical components in the Fourth aquifer is the dissolution of calcite,dolomite and gypsum and the alternating adsorption of cations;The formation of the main hydrochemical components in the coal measure aquifer is desulfation and cation alternating adsorption;The formation of the main hydrochemical components in the Taihui aquifer is the dissolution of calcite,dolomite and gypsum,the oxidation of pyrite,followed by the cation alternating adsorption.（3）Mineral composition directly affects the chemical composition of groundwater.The Fourth aquifer is affected by the mineral composition and groundwater flow conditions,the dissolution changes from strong to weak along the groundwater flow,and the cation alternating adsorption changes from weak to strong.The coal measure aquifer is affected by the region’s geological structure.The dissolution of coal measure water is weak,and the desulfation and cation alternating adsorption are strong in the northeast,but opposite in the southwest.The Taihui aquifer is jointly controlled by groundwater flow conditions and regional structure,and the formation of hydrochemical composition is similar to that of the coal measure aquifer.There is a strong hydraulic connection between the coal measure aquifer,the Fourth aquifer and the Taihui aquifer.The mine drainage enhances the formation of hydrochemical components containing Na⁺,Cl^-and HCO₃^-.（4）By quantitatively calculating the formation of hydrochemical composition in the groundwater runoff process of each aquifer,the reverse simulation is carried out,which is consistent with the qualitative analysis results.Figure[22]Table[13]Reference[101]...