Study On Three-dimensional Online Monitoring Technology For Landfill Leakage Pollution

Municipal solid waste pollution is the main restrictive factor for city development in China. At present, landfill method is a widely-used method for municipal solid waste disposal, which disposes over 90% of the whole quantity. But according to operation data of lots of landfills in and abroad, landfill method is likely to cause serious pollution to underground environment (groundwater, underground soil). So it is an urgent task for environmentalists to study how to monitor and prevent underground environment from further pollution by landfill.Landfill leakage monitoring technology now in use include groundwater monitoring method, water lance technology, two-electrode method, tracers method, diffusion hoses method and electrode grid method. A three-dimensional online monitoring system put below liner system in advance is put forward based on the detail analysis of these methods. This system is an improvement of electrode grid method, which can not only confirm the occurrence of leakage, pinpoint the leakage location and estimate the numbers of the leakage, but also detect the shape of leachate plume according to the abnormal area of the profiles corresponding with spatial distribution of polluted area.According to literature search and theoretical analysis, the factors affecting electric properties of underground media below landfill include water content, electric conductivity of pore water, saturation and types of soil; when leakage occurs in landfill, the physical and chemical properties of soils will change, which leads to changes of electricity and natural potential of underground soil. On the basis of this premise and construction characters of landfill, design of three-dimensional online monitoring system is laid out, which discusses the structure of system, the position ofelectrical sensor and the flow chart of the whole system.Indoor simulation experiments are conducted using a glass-steel tank in order to testify if the apparent resistivity of unsaturated sandy soil layer decreases after the distilled water leakage. Leachate containing a large amount of oil is used to stimulate seepage process and a reasonable resistivity is put forward. On the foundation of this, leachate from XiaoJianxi landfill in QingDao is used to study the reflection ability of three-dimensional online monitoring system.The results show that electricity of soil changes on the percolation of leachate. In the simulation experiments using the leachate addressed above, low resistivity area is formed due to leachate percolation. The possible location of leakage can be determined as the center of low resistivity area based on the distribution feature and changing trend of low resistivity area on electrical resistivity cross sections. That actual diffusion area is proportional to abnomal area of resistivity is verified. Dynamic monitoring of polluted area can be achieved on account of the regulation that low resistivity area expands with time. According to the boundary of the resistivity of pollutant, the three-dimensional distribution of leachate plume can be deduced.