Mechanism Investigation and Numerical Modeling Study on Environmental Groundwater Changes in Yongcheng Mining Area,China
Supervisor:wan li liang si hai
The large-scale development of coal resources in the Yongcheng mining area has provided a powerful impetus to the economic development of Yongcheng,even the eastern region of Henan Province.However,the environmental geological problems such as groundwater quantity and quality caused by the coal mining activities have aggravated the shortage of groundwater resources and seriously restricted people’s life and production activities.Therefore,to study on mechanism of groundwater environment changes under the influence of mining activities,and to explore the risk of pollution in the water source area,provides valuable assistance to the prevention and control of groundwater environment in the mining area.Based on the collection of hydrology,meteorology,geological,hydrogeological and other related materials in the study area,combining with field investigations and laboratory tests,this study evaluates groundwater environment,takes the Cheji Coal Mine and Shenhuo Industrial Park water supply sources as the key research object,and establishs the spatial distribution of multiple aquifers with hydraulic linkages that may be affected by coal mining activities.The evolution of aquifer flow system and the solute transport of the marker pollutants in the point source of the coal gangue stacking yard,line source of the mine drainage pipeline and surface source of the coal mining subsidence area that are generated in coal mining activities is simulated by using groundwater three-dimensional numerical simulation software,which is the Visual Modflow.Finally,the pollution risk of the water supply source in Shenhuo Industrial Park was analyzed,and the control measures of groundwater environmental was proposed by impacting in coal mining activities.The main contents of this research include the following aspects:1.The water level and water quality monitoring points which is in the three stages of abundance,level and dry season are arranged,and the groundwater environment is evaluated based on the test results.The results show that the exploitation of shallow groundwater in the study area is mainly used for agricultural irrigation.The variation of groundwater level in the three stages is about 2.0m.May be affected by coal mining activities,the total dissolved solids,total hardness,sulfate and fluoride of most monitoring points are above the standard.and the water quality varies little with the season.2.The existence of the“three zones”caused by the coal mining does not perforate through the upper aquifers.Owing to fissure-conducting of aquifer floor causing by backstoping,the limestone groundwater is vertical cross-flow supplement to the coal-bearing strata.Through the analysis of the monitoring results of the mine water inflow over the years,the water inflow is steadily stable to 500m~3/h,and the water level of the underlying limestone aquifer is continuously decreasing.The quality of drainage water is extremely poor,and it can still meet the different demand water after treatment system.Through monitoring the water quality around the coal gangue stacking yard,the farther the monitoring point is from the site is,the smaller the concentration of total dissolved solids,sulfate and heavy metal manganese.The water quality of the coal mining subsidence area where is filled with coal gangue is worse than that outside of the area,and may have been contaminated by coal gangue.3.Starting from the construction of the conceptual model of the study area,the spatial distribution of multiple aquifer systems including the Quaternary aquifer,the middle and deep aquifer,the sandstone fissure aquifer and the limestone aquifer is described.With expressing boundary and initial conditions of the groundwater flow system model,and using the groundwater level monitoring data to identificate and verificate,the model reproduces the natural flow field before the coal mine construction,analyzes the relationship between the supply and discharge and the water balance of the current annual water flow system,and predicts evolution of the groundwater flow system for 30 years.The simulation results show that the water level in the center of the funnel reaches-26.2m due to the continuous pumping of the Shenhuo Industrial Park water supply sources and the average annual drop is 1.1~1.2m during the 30 years.Because of the drainage increasing the head pressure difference,the limestone aquifer continuously suppliing the fracture water of sandstone,and the lateral recharging less,the water level at the main and auxiliary wells for 30 years will drop by about 4.7m per year.4.With using the MT3D module,the pollutant transport model is established based on the water flow model,which the sulfate ion is set as the marker pollutant.It analyzes the process of pollutant transport in which the coal gangue stacking yard is set as point source,mine drainage pipeline as line source,coal mining subsidence treatment area as surface source,delineates the pollution range at different time points,and discusses the pollution risk of the pumping layer in the water supply source.(1)The coal gangue stacking yard continues to supply constant concentration,and the formed elliptical pollution halo spreads along the groundwater flow to the southeast.After 30 years,the area of halo is about 58239 m~2.(2)For the infiltration and pollution of the mine drainage pipeline,two scenarios of continuous leakage of small flow and large instantaneous flow of accident nodes are set.In scenario one,the flow of pollutants into groundwater is small,but there is a continuous supply source,so the width of the pollution zone is gradually increased,and the maximum width of the pollution zone after 30 years is426m.In scenario two,a large number of pollutants leaked in a short period of time,and with the pollution range migrating,the peak concentration of the pollution halo center will continuously reduce to 40.6 mg/L,and the migration distance of the center will be171 m.(3)After the coal gangue releasing the pollutants in the subsidence area,it will migrate along the water flow to the Tuo River,and the area of pollution increase by 50%in 30 years.After vertically penetrating into the underlying first weak aquifer,the pollutants mainly spread horizontally,which the pumping layer in the water source is basically not affected.5.On the basis of the changes investion of groundwater environment in the mining area under the influence of coal mining activities,the protection needs of the water source and the wells around the mining area are analyzed,and the countermeasures for the prevention and control of the groundwater environment are put forward.With the main principles of scientific emission reduction and comprehensive utilization,the groundwater and soil pollution control and rehabilitation need to be carried out,and to strengthen groundwater environmental monitoring.The research results have important theoretical reference significance for the study on groundwater environment change mechanism in coal mining activities in the future,and provide guiding opinions for the development and utilization of groundwater resources and management decision-making of environmental protection.