Water Chemistry Characteristics And Flow Field Simulation Of The Overlying Aquifer In The Bulianta Mine

Erdos in Inner Mongolia Autonomous Region is rich in natural resources and one of the major energy bases in China.The large-scale exploitation of coal resources in Shendong Mining Area of Erdos City has provided strong support for the economic and social development of Erdos City and Yushen area.However,the high-intensity coal mining also brings a series of groundwater resource shortage problems to the local area,and the changes of water quality and quantity caused by mining have become the main problems restricting the continued development of local society and economy.Therefore,in this paper,the study of the evolution of the aquifer system under the driving effect of coal mining is carried out in the study area of the more representative Bulianta mine under the Shendong mining area to investigate the changes of groundwater quality,which can efficiently and reasonably propose groundwater management plans and water resources protection measures.In this study,based on the collection of geographic,geological,meteorological,regional hydrogeological,agricultural and animal husbandry data in the study area,we analyzed and evaluated the changes of groundwater flow field,groundwater chemical components,and groundwater solute transport in the Bulianta mine area by combining field investigation and indoor tests,and established a conceptual model of hydrogeology.Through the MODFLOW groundwater flow simulation module embedded in GMS,the flow changes of the overlying aquifer in the mine area are simulated under the effect of high-intensity mining for many years;the hydraulic connection between the overlying aquifer of the coal mining system is judged by calculating the influence height of the fall zone and the fracture zone and combining with conventional ions,trace ions and hydrogen and oxygen isotopes;the characteristics of the chemical components of groundwater in the study area are measured.By measuring the characteristics of the chemical components of groundwater in the study area,the spatial distribution of characteristic pollutants in the mine area and coal gangue and slag dumping area is studied,and the management measures of groundwater environment under the action of mining are proposed.The main contents of this study are as follows:（1）Groundwater sampling points were laid in the shallow aquifer of the study area,and the Ulanmulun River and its tributaries were taken as the grid and extended appropriately for grid sampling,and the water samples were tested,and the test indexes were Na⁺、K⁺、Ca²⁺、Mg²⁺、F^-、Cl^-、SO₄^2-、NO^-₃、CO₃^2-、HCO^-₃、TDS、p H、δD、δ¹⁸O and ³H,total of 15 indicators.The results show that the groundwater quality of the groundwater system is generally good,the surface runoff is from northwest to southeast.The upstream aquifer particles are larger and the downstream aquifer particles are smaller.The pore space of the upstream to downstream aquifer gradually decreases,resulting in the dissolution and filtration effect gradually becoming stronger as the pore space becomes smaller.The mineralization of groundwater in the study area is high and it is a weakly alkaline freshwater environment.（2）The spatial transport and distribution of NO₃^-,SO₄^2-and TDS in the study area were analyzed by geographic information system.The results showed that under the driving of coal mining,the SO₄^2-in groundwater in the study area showed a trend of enrichment from upstream to downstream,and the concentration reached the highest in the downstream area.NO₃^-plasma and components showed the trend of the highest concentration in the range of 7 km radius centered on the mining area and gradually decreasing to the surrounding area.The overall trend of TDS is centered on the Bulianta mining area and other adjacent mining areas,showing a trend of multi-point enrichment and decreasing to the surrounding areas.（3）Through the analysis of conventional water chemical components,trace water chemical components,deuterium oxygen isotopes of water samples,and combined with hydrogeological data,it is speculated that under the action of mining,the overlying Quaternary pore aquifer,Zhidan Group fissure aquifer,and Zhiluo Group fissure aquifer in the coal bed of the Bulianta mine area appear to be linked,and the aquifer and aquifer are connected to each other,and there is cross-flow recharge directly to the coal-bearing strata,which is one of the reasons for the poor groundwater quality of the coal-bearing strata.（4）The conceptual model of the study area was established by analyzing the geological,hydrogeological and meteorological data of the study area and determining the geological structure,spatial spreading,boundary type and source-sink term of the study area.The model was generalized into the Quaternary aquifer,Zhidan Group aquifer,sandpaper mudstone weakly permeable layer and Zhiluo Group aquifer from top to bottom,with known flow recharge boundary on the west side,constant flow discharge boundary on the east side and zero flow boundary on the north and south side,and the model type was homogeneous anisotropic three-dimensional unsteady flow model.The model prediction shows that there is no significant change in groundwater level in 2020-2046 under the existing mining conditions,but mining leads to a change in the local groundwater circulation pattern to form a landing funnel,forming a local groundwater circulation system to accelerate groundwater circulation.（5）On the basis of groundwater chemical characteristics,aquifer structure variation and groundwater flow field trends,and based on the protection needs of groundwater in the mining area of Bulianta under the influence of mining,a reasonable management plan for the groundwater environment is proposed,with scientific discharge,scientific emission reduction,reuse and precise positioning as the basic guidelines,work on the environmental management of groundwater in the study area and the precise positioning treatment of sudden water in the mining area is carried out,and groundwater monitoring is strengthened at a later stage to achieve long-term rational planning and timely management.