Study On Groundwater Circulation-Hydrochemical Evolution And Mixing Model Under Mining-induced Disturbance In Suxian-linhuan Mining Area

Mining-induced disturbance will change the hydrodynamic condition of the groundwater system and destroy the hydrochemical environment in North China coal mining area. However, the study of hydrochemistry of multi-aquifer groundwater system in mining areas has not yet analyzed the relationship between hydrodynamics and hydrochemistry under the condition of mining-induced disturbance in large-scale and time-space. Therefore, it can not reveal the original face and development trend of hydrochemical environment, and it is more difficult to determine the characteristics of groundwater circulation and evolution, which will result in much blindness in prevention and control of mine water disaster and in utilization and protection of water resources. On this basis, the typical North China coal mine area——Suxian-Linhuan Mining Area is choosed as the research area, and the groundwater system of the mine area is taken as the research object, and the main water-inrush aquifers in the groundwater system are taken as the research demonstration. The site research, data collection, indoor testing, system development and theoretical analysis are adopted as the combination of research methods. Firstly, water-rock interaction mechanism and hydrochemical evolution law of the main water-inrush aquifers under the influence of mining are studied by means of tracer technique such as typical isotope and conventional ions. Secondly, according to the stable and similar geochemical characteristics of rare earth elements, considering the different hydrogeochemical environments of main water-inrush aquifers in the mine area, the different geochemical behaviors of rare earth elements in water-rock interaction of main water-inrush aquifers are analyzed, and the groundwater circulation pattern in main water-inrush aquifers is proposed. Thirdly, based on the study of hydrochemical-hydrological changing relationship under the mining-induced disturbance, the circulation process and supply source of groundwater in the mining area are analyzed by the tracing technique of the hydrogen and oxygen stable isotopes and hydrochemistry ions, and the mixed groundwater recharge end members are reasonably confirmed, the calculation model of the mixing ratio of the groundwater recharge end members is proposed. The main research results are as follows:(1) Based on ArcGIS and its secondary development platform, a hydrological and geochemical evolution identification system for groundwater in mining area are established by principal component analysis to study the changing relationship between hydrochemistry and groundwater circulation.(2) The main water-rock interaction mechanism of the main water-inrush aquifers is traced by isotopes (87Sr/86Sr,34S,13C) and conventional ions (Na++K+, Ca2+,Mg2+,HCO3-, Cl-, SO42- , CO32-). The cation exchange and desulphurization are the most significant in the coal sandstone fissure aquifer, while carbonate, sulfate dissolution and pyrite oxidation are the most significant in the fourth aquifer of unconsolidated formation, the Carboniferous karst aquifer of Taiyuan formation and the Ordovician karst aquifer. Under the influence of mining, the main water-rock interaction in the coal sandstone fissure aquifer and the Ordovician karst aquifer is weakened, and the main water-rock interaction of the fourth aquifer of unconsolidated formation and the Carboniferous karst aquifer of Taiyuan formation is strengthened or weakened, and the degree of strengthening or weakening depends on the existence of geological and hydrogeological background conditions.(3) By contrasting the principal component analysises containing the analysis variables such as geochemical parameters of rare earth elements (LREE/HREE,(La/Yb)N, ?Eu, ?Ce, (La/Sm)N, (Gd/Yb)N, Eu/Sm) and conventional ions (Na++K+, Ca2+,Mg2+, HCO3-, Cl-, SO42-, CO32-),it can be seen that the 8Eu, LREE/HREE, Eu/Sm and?Ce of groundwater in the main water-inrush aquifers are related to the dissolution of sulfate and carbonate in the aquifers and the pyrite oxidation, and (La/Yb)N and(Gd/Yb)N are related to the cation exchange and desulfurization in the aquifers. Based on the analysis of distribution and hydrogeochemical behavior of rare earth elements,the circulation pattern of groundwater in the mine area is divided into three kinds of seepage paths (nearly horizontal seepage,nearly vertical seepage and mixed seepage).(4) Based on the union tracing of isotopes (D,180) and conventional ions (Na++K+,Ca2+,Mg2+,HCO3-, Cl-, SO42-, CO32-), the independent recharge end members of groundwater in the mining area can be confirmed to be the direct infiltration of atmospheric precipitation, the retention infiltration of atmospheric precipitation, and the ancient groundwater mixing. On this basis,a calculation model of the mixing ratio of groundwater recharge end members is established for the main water-inrush aquifers in the mining area, which application effect is good.The research results will lay a foundation for the prediction of water inrush and for protection and utilization of water resources in the mining area, and will expand the application field of the hydrogeochemical theory.