Simulation Study On Prevention And Control Of Groundwater Pollution By Different Anti-seepage Measures

The prevention and control measures of groundwater pollution mainly include bottom seepage control and lateral seepage control.The bottom seepage control also includes the unsaturated zone natural seepage control and the artificial level seepage control.Under the condition of limited seepage control effect of natural unsaturated zone,it is an important prevention and control measure to prevent polluted wastewater infiltration by artificially setting horizontal impervious layer on the bottom of potential pollution source.However,we will need lateral seepage control technology to reduce the pollution risk due to the aging or corrosion of bottom seepage control.The most commonly used lateral seepage control techniques include hydraulic capture wells and vertical cutoff walls.The construction cost of the vertical cutoff wall is very high and the construction quality is unstable,so the hydraulic capture well which is more economical and easy to be monitored can be considered to replace the vertical impervious wall’s function in the suitable site.Based on the advantages and disadvantages of different hydrogeological conditions and seepage prevention measures,this paper systematically studies the effects of different bottom and lateral seepage prevention measures,thus providing support for the different conditions to select effective and economically reasonable groundwater pollution control measures and effective groundwater monitoring schemes.Based on the typical large unsaturated zone area of a metal smelting plant,the saturated-unsaturated flow and solute transport model was constructed by FEFLOW,The unsaturated zone thickness and the permeability of unsaturated zone medium and the influence of unsaturated zone lithology on the natural seepage control effect of different unsaturated zones such as pollutant adsorption performance,furthermore,the effects of natural seepage control and bottom artificial seepage control in unsaturated zone are studied in this paper,which provides a basis for whether the bottom seepage control should be set under different conditions.The results show that,for contaminants that do not adsorb in unsaturated zones,when unsaturated zone medium is poor permeability of silty clay,silt,compared to sand and medium coarse sand,unsaturated zone can greatly delay the pollution into the saturated aquifer,but still can not be completely equivalent to the level of impervious layer,so the bottom level of seepage is needed.For the contaminants in the unsaturated zone,when the unsaturated zone is silty clay,silty sand,and the thickness is large,the impervious capacity of unsaturated zone is strong,and the pollutant will not reach the saturated aquifer within a certain age.Therefore,the time of detecting pollutant in saturated zone under this conditions behind the occurrence time of site pollution,and the pollution monitoring of unsaturated zone must be intensified in the area.Based on the example model,using GMS’s MODFLOW and MT3DMS to construct saturated zone flow and solute transport model,the paper studies how to optimize setting up hydraulic capture wells under different permeability and aquifer thickness,so as to make the pollution control effect of vertical cutoff wall.The results of the example model are applied to the comparative study of the pollution control effect between the hydraulic capture wells and the vertical cutoff wall under the actual site conditions of a hazardous waste landfill in Jiangsu Province,which provides reference for the selection of seepage prevention measures for similar projects.The results show that,when the thickness of the aquifer is about m=5m,the water medium is fine sand or the permeability is worse,it is difficult to prevent and control the pollutant,and it is suggested to use the vertical cutoff wall.In the landfill,where the thickness of the aquifer is m=20m,the hydraulic capture well can be used instead of the vertical cutoff wall when the aqueous medium is fine sand,medium coarse sand and better permeable aqueous medium.In the example,both the hydraulic capture wells and the vertical cutoff wall can effectively control the migration and diffusion of the pollutant,and the anti-seepage effect of the hydraulic capture well is slightly worse than that of the cutoff wall,but only a few meters.Considering the economic feasibility of intercepting well and controllability of construction quality,it is suggested to use hydraulic capture well.