| The garbage heap of landfills will produce much leachate and the leachate contains all kinds of hazardous substances. Once leaking it will cause serious harm of the surrounding soil and groundwater. Groundwater accounts for only one-third of China’s total water resources, but 90 percent of the groundwater are subject to different degrees of pollution. At home and abroad leachate contamination of groundwater environmental events often occur and caused immeasurable damage on people’s life and production. Therefore, factors affecting landfill pollution laws and Impervious are very necessary.As for domestic researching about leachate contamination of groundwater started late, there are few comprehensive studies of groundwater pollution, governance and seepage. Based on this paper describes the theoretical basis and solving methods of the numerical modeling of groundwater systems. And the discrete basic principle of the numerical simulation software model visual modflow, the finite difference methods for solving the basic steps and the hydrodynamic dispersion and numerical modeling of the process have been described in detail. Based on this the three-dimensional mathematical model is established with the analysis of hydrogeological data in study area. Coupling the groundwater flowing model visual modflow with the multi component solute transport model MT3 DMS, this paper uses Cl- for the representative contaminant to predict the future characteristics and its range. Then using this model explores the effect on the arrangement position and spacing of single-well pumping and multi-well pumping on groundwater pollution, introducing the problem of leakage and seepage technology impermeable material, mechanism of action and different impermeable layer impermeable systems. Established a two-dimensional model of the landfill, using seep/w finite element analysis software analyzes the impact of leachate levels, impervious curtain thickness and permeability of the size of the seepage. The following conclusions:(1) With the migration of the spread of pollutants, the leachate mainly pollutes along the direction of groundwater flowing in far field surface water and shallow groundwater, but not deep groundwater contamination and pollution upstream; if there is a lake in the area, the lake will be a long-term capture of pollutants, contaminants will not migrate, but the lake will be contaminated; The deep groundwater is polluted not easily owing to the blocking of soil, but once the contamination is difficult to control.(2) Pumping result not only relates to well spacing but also the number of wells and related layout spacing. When the placement pitches are large, the number of less well is more advantage and on the contrary the numbers of well is less advantage. The larger placement pitches of wells are not the better. The optimum laying pace is 70 m in this simulation.(3) It is unreasonable based on hydraulic engineering specifications for landfill seepage curtain to design; in the case that the geological conditions are good permeability aquitard 1×10-7cm/s, the impervious curtain factor should be greater than 1×10-8cm/s, a value between 1×10-6~1×10-7cm/s; with selecting the landfill site, underground impermeable layer coefficient of less than 1×10-7cm/s of soil should be selected; when the curtain thickness is narrow, contaminants can easily puncture the top of the soil into the downstream seepage curtain, at this time, in order to simplify the construction of impervious the curtain thickness at the top can be widened.The simulation results of this paper show that visual modflow,MT3 DMS and Geo-studio software analysis the numerical modeling to improve the efficiency and simplify the pre-processing and post-processing of the data, with a wide range of application, while providing a reference selection on the study of groundwater contamination law and the choosing of seepage-proofing measures. |
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