Groundwater Pollution Analysis And Pollutant Migration Simulation In Jiayuan Manganese Slag Heap In Chongqing

In Chongqing Xiushan County,23 manganese slag banks have been formed by years of mining,with a total storage capacity of more than 10 million tons of manganese slag.The manganese slag stored in the open air will easily pollute the groundwater after precipitation leaching.In this paper,the geological environment and hydrogeological conditions of the study area were outlined,taking the Jiayuan Mining Manganese Slag Dump in Xiushan County as the research object.Through water sample collection and testing,the groundwater pollution characteristics were analyzed and the quality of groundwater in the area was evaluated,based on which the migration of major pollutants in the next ten years was predicted using Visual MODFLOW4.0 software.The main research contents and results of this paper are as follows:（1）The type of groundwater in the study area is carbonate rock fissure cave water and clastic rock interspersed with carbonate rock fissure cave water,which mainly receives infiltration recharge from atmospheric precipitation and is discharged in the form of springs and lateral runoff,and the direction of runoff is north-east;the chemical type of water in the study area is HCO₃-Ca·Mg type,and the Gibbs diagram method,ion correlation analysis and ion ratio coefficient show that the groundwater in the area The chemical composition is influenced by the weathering and dissolution filtration of carbonate rocks such as tuffs and dolomitic tuffs.（2）After investigation,the main pollution factors in the groundwater were Mn and NH₃-N.The exceedance rate of Mn in the tested water samples was 50%,with the maximum concentration value exceeding 8.7 times,and the exceedance rate of NH₃-N was 14.2%,with the maximum concentration value exceeding 1.6 times.Through the connectivity test and geophysical exploration,it was confirmed that there is connectivity of groundwater in the shallow part of the slag field and the surrounding area,and runoff through the surface fracture zone to the direction of leachate collection pond,and finally runoff through the dissolution fracture zone to the deep karst channel,and discharge in the form of spring in the northwest of the slag field.（3）The single factor index method,Nemero index method and entropy value-fuzzy comprehensive evaluation method were used to evaluate the quality of groundwater,which showed that the groundwater was mainly polluted by manganese and ammonia nitrogen,and the calculation determined that Class IV water accounted for 60%of the total water samples,and the water quality condition was poor and not suitable for drinking water.（4）Using Visual MODFLOW4.0 to establish the groundwater flow model and pollutant transport model of the slag dumps,the simulation to the 10th year,the pollutants have caused serious pollution to the groundwater environment,the emergence of Class V water,without treatment will not be used for any purpose.In addition,with the passage of time,the pollution caused by the manganese slag dump is expanding and the pollution level continues to increase,which will cause the pollution of the downstream water body Longdong River,judging from the groundwater flow direction.At present,the slag yard is still in use,and the amount of slag pile is increasing day by day,so the manganese slag yard is in urgent need of safe disposal and resource utilization to reduce the pollution to the groundwater environment.