Mechanism Of Landfill Leachate Leakage And Its Impact On Groundwater Environment

Sanitary landfill is currently the mainstream way to deal with the problem of municipal solid waste,and the landfill method also brings many environmental problems.Once the landfill leachate is leaked,it will seep into the underground water through the vadose zone,which will affect the underground environment and even endanger human health.Therefore,study the migration and transformation regularity of pollutants in the vadose zone,Determine the time and concentration value of pollutants migrating to groundwater after passing through the vadose zone,and provide effective basis for groundwater prevention and control.Based on a landfill site in Hebei Province,this thesis selects ammonia nitrogen as the characteristic pollutant to carry out research.Through indoor experiments,it studies the migration regularity of ammonia nitrogen in the soil media of different vadose zones.It uses Hydras-1D software to simulate and verify with the indoor experiments.After verifying the reliability of the model,the migration and changes of ammonia nitrogen pollutions in the soil of vadose zone under different working conditions and situations is predicted,and predicts the time and concentration values of its migration to groundwater.The main research content of this thesis is as follows:(1)Based on the solute transport mechanism,the indoor soil column leaching experiment was carried out,the chloride ion breakthrough curve was obtained through the chloride ion tracer experiment,and the longitudinal coefficient and longitudinal dispersivity of soil media in different vadose zones were calculated.Subsequently,the retardation coefficient and distribution coefficient were calculated from the ammonia nitrogen leaching experiment,and the ammonia nitrogen breakthrough curve was similar to the chloride ion breakthrough curve in the tracer experiment,but the ammonia nitrogen breakthrough time was long,which was caused by the convection dispersion and adsorption of ammonia nitrogen pollutants by the soil,and delayed its migration time in the soil.(2)Hydras-1D software is used for simulation,and the parameters are adjusted and verified through the indoor experimental data.The good fitting effect between the measured value and the simulated value is obtained,and the accuracy of the model establishment is confirmed,which can be used for simulation prediction.Through conducting parameter sensitivity analysis on longitudinal dispersivity,saturated water content,permeability coefficient,distribution coefficient and molecular diffusion coefficient,it is found that the change of permeability coefficient has the greatest impact on the model simulation results,while the change of diffusion coefficient has the smallest impact on the model simulation results.(3)After verifying the model,a model of ammonia nitrogen transport in the LWHZ2 vadose zone in the study area was established,and the continuous point source and discontinuous point source pollution under abnormal conditions were simulated and predicted.It was found that although the ammonia nitrogen concentration values in groundwater exceeded the Class III and IV standards in turn for the same time under the two conditions,the continuous point source pollution had great harm to the aeration zone and groundwater.In addition,when only changing the concentration value of the pollution source,the ammonia nitrogen concentration value at the groundwater level will also expand or decrease by the same multiple as the concentration value of the pollution source,but the reduction coefficient and reduction rate will not change;Only changing the structure of the vadose zone,the thicker the silty clay layer in the soil medium of the vadose zone,the better the attenuation effect of ammonia nitrogen pollutants;When only the leakage time is changed,the shorter the leakage time,the smaller the impact on the vadose zone and groundwater environment,and the smaller the concentration value transferred to groundwater.