| Pingshuo mining area is located in the north of Ningwu coalfield,which is one of the largest and most modernized coal production bases in China.However,with the extension of mining depth and range,the water cycle is accelerated;the groundwater level drops sharply;the water inflow keeps increasing;the water quality deteriorates,and the ecological environment problems become increasingly prominent.These problems have become the main factor restricting the safe and sustainable development of mining enterprises,and also threaten the safety of water for production and living in mining areas.Therefore,it is very urgent to systematically and accurately study the hydrochemical status and hydraulic connection of different water bodies in the mining area,and the distribution of groundwater level.This study has important practical significance and scientific value for the coordinated development of coal and water,the prevention and management of water disasters,drinking water safety and the reasonable development and utilization of water resources in the mining area.This paper takes the basin of Pingshuo mining area as the study object,The 468 samples of surface water,groundwater and mine water were collected in 2020-2021 and the methods of hydrochemistry,isotope and numerical simulation were applied to analyze the hydrochemical characteristics,hydrochemical types,the cause of formation of hydrochemistry and the controlling factors,the spatial and temporal distribution characteristics of fluorine,sources and controlling factors of fluorine in different water bodies.The isotopic characteristics,spatial and temporal distribution characteristics and indicative significance of water cycle of different water bodies were explored.The groundwater flow model of the study area was established to predict the change of water level in coal measures aquifers driven by coal mining.The main conclusions were as follows:(1)Surface water,groundwater and mine water are nearly neutral to weakly alkaline.The dominant anion in surface water and mine water is SO42-,whereas the dominant anion in groundwater is HCO3-,and Ca2+ is the dominant cation in all water bodies.The main hydrochemical types of surface water are SO4-HCO3-Mg-Ca-Na,SO4-HCO3-Ca-Mg,HCO3-SO4-Mg-Na-Ca,and mine water type is SO4-HCO3-Ca-Mg.The main types of shallow groundwater are HCO3-Ca-Mg,HCO3-SO4-Ca-Mg,HCO3-Na-Mg,SO4-HCO3-Ca-Mg,HCO3-SO4-Ca-Mg and HCO3-Na,and the deep groundwater type are HCO3-Ca-Mg and HCO3-SO4-Ca-Mg.The hydrochemistry of water bodies was mainly affected by the weathering and dissolution of carbonate rocks,coal mining activities as well as the weathering and dissolution of fluorine-bearing minerals.Human activities such as coal mining and industry and agriculture accelerate the amount of water and water chemistry conversion among different water bodies,especially shallow groundwater.(2)The concentration of F-in water is ranges from 0.10 to 1.76 mg·L-1,and the F-concentration of 42%of the shallow groundwater exceeds the national permissible limit for drinking.In terms of spatial and temporal distribution,the average concentration of F-in groundwater from northwest to southeast shows an increasing trend,and the concentration of F-was higher in March and August.The shallow groundwater with high fluorine content is characterized by alkalinity and high Na+.F-enrichment is mainly affected by coal mining activities and weathering and dissolution of fluorine-bearing minerals,and calcite saturation accelerates the weathering and dissolution of fluorine-bearing minerals.(3)The δD and δ18O in surface water and mine water are higher in summer than in winter.The seasonal difference of δD and δ18O in groundwater is not obvious.The hydrogen and oxygen isotope values of surface water increase along the way,but are partially depleted by mine water.The hydrogen and oxygen isotope values of groundwater gradually increase along the direction of runoff.The hydrogen and oxygen isotope values in coal mining areas are obviously higher than those in non-mining area.Due to seasonal effects,the area of high hydrogen and oxygen isotope values of shallow groundwater in August increase significantly compared with that in December.The relationship between δ18O and δD shows that all kinds of water are directly or indirectly recharged by atmospheric precipitation.Surface water is affected by evaporative fractionation after being recharged by atmospheric precipitation.The recharge sources of shallow groundwater are complicated.The deep groundwater is recharged by shallow groundwater and surface water due to the water-conducting fracture zone formed by coal mining.Mine water is recharged by surface water,shallow groundwater and deep groundwater.Based on the principle of mass conservation of hydrogen and oxygen isotopes,the application of the MixSIAR mixed model reveals that deep groundwater is the main recharge source of mine water,accounting for 61.60%-67.20%.(4)The groundwater flow model is established by using groundwater numerical simulation software GMS.This model is used to simulate and predict the groundwater level of coal measure aquifer in the study area from 2015 to 2030.The research shows that the water level of coal measure aquifer decreases continuously,with a decreasing range of 0.5-12 m·a-1 due to the exploitation of coal resources.The closer to the coal mining area,the more the water level drops.The variation trend of water level shows that the rate of decline is fast in the early stage,and slowdown in the late stage,and finally tend to equilibrium.The mining of coal also causes the change of flow field in the Pingshuo mining area basin,and cone of depression has come into being.In 2020,as coal mining continues,the cone of depression begins to connect,resulting in an overall drop of the groundwater level and a sharp decrease in water resources. |
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