A Numerical Simulation Study On The Remediation Of Ammonia Nitrogen Pollution In Groundwater From A Landfill In A Coastal Area

The treatment and remediation of shallow aquifers contaminated by landfills is a challenging topic for groundwater management in coastal plains.To address this problem,To address this problem,this study took an informal landfill site in Tianjin as the research area,and used high-density resistivity to determine the natural stratum of the landfill in the coastal plain area through traditional geophysical techniques for resource investigation.Stability and continuity,and determine the size and location of the leakage channel,to provide basic geological data for subsequent numerical simulation analysis.Taking ammonia nitrogen in groundwater as the main research object,on the basis of systematic analysis of the geological and hydrogeological conditions in the study area,the field monitors the dynamic changes of groundwater ammonia nitrogen concentration around the landfill,and reveals the migration and transformation of ammonia nitrogen in the process of leachate infiltration into groundwater.,And use numerical simulation technology to predict the spatial and temporal distribution characteristics and evolution trend of ammonia nitrogen concentration in groundwater,on this basis,extraction control and simulation of pollution control schemes and particle tracing such as anti-seepage wall-isolating funnel-water gate system repair simulation,and particle tracing,Optimize the design of groundwater remediation schemes for landfills in coastal areas,and provide references for the prevention and control of groundwater pollution in landfills in coastal plains.The thesis achieved the following research results:（1）The model results show that the movement of pollutants is mainly affected by the control of surface water and terrain,and the groundwater in the northern part of the landfill is almost not polluted.In the southeastern aquifer,the pollution level is highest within 200 m south of the landfill,and the concentration of pollutants decreases with the distance from the landfill.The simulation results are helpful for us to understand the migration and spatial distribution of NH₄⁺-N concentration（i.e.,gradient）and the impact of hydro-stratigraphy,atmospheric precipitation,and surface water bodies in the study area.Impact,delineate the area and scope of groundwater NH₄⁺-N pollution impact in the study area.（2）Consider the hydrogeological conditions of the site and optimize the design of the groundwater remediation plan in the study area based on numerical simulation.Curtain grouting engineering design was carried out around the landfill,the underground impervious wall to the coastal aquifer landfill aquifer flow field,ammonia nitrogen distribution,and the permeability coefficient and thickness of the impervious wall,pollution source concentration,etc.Due to the influence of the wall performance,an optimized construction plan for a seepage control wall to control ammonia-nitrogen pollution in the groundwater of the landfill was proposed.On this basis,the pollution control and repair technologies were compared and selected.Based on the numerical simulation of ammonia and nitrogen migration and particle tracing results under the condition of vertical anti-seepage walls,a PRB in-situ repair wall（separating funnel）was set up 200 m south of the landfill-Water gate system),to treat the contaminated groundwater and prevent the landfill from continuing to pollute the downstream groundwater.The numerical results show that the anti-seepage wall-water funnel-water gate repair system is good for the groundwater repair in the study area and can be effective Reduce the groundwater ammonia nitrogen concentration in the study area.