| On one hand,at present,the study on the transportation of leachate from landfill is gone on in some plain city only,but the research in this respect in the mountain city has not been launched yet. The specific complicated geological conditions in the mountain city have determined the complexity of running rule of leachate. On the other hand,the output of leachate is very big with the afflux of surface water in mountain cities . And the weathering fractures of the rock stratum in the landfills site develop well. Leachate will become the main pollution sources of river,and it will endanger to people's health in various degree,when it infiltrates into the groundwater through weathering fractures. So it is necessary to systematically study the transportation of leachate from landfills of mountain city,find out corresponding running rules,and use them to guiding the settlement of some environmental problems in these landfills. At first,this text sets up flow model of groundwater and transportation model of solute,which is suitable for complex geological conditions in mountain city,after analyzing complicated geological and hydrographic conditions of the mountain regions. These two models are coupled into one running model of leachate,and be verified in the simulation of Qilong landfill. Then the writer collected and analyzed the materials about such respects as the geological,hydrographic and environmental conditions of Qilong landfill,simulated the transportation of the leachate in Qilong landfill with Processing Modflow software basing on finite difference method. Through simulating and analyzing,this text summarized several basic rules of the transportation of the leachate around the landfill: (1)The main transportation direction of leachate is the groundwater direction. The fracture plays a very strong role to the transportation of leachate. On the fracture site,leachate moves very fast,and the density of leachate is very high also;In the region where the groundwater is very weak,the dispersion is one of the main transport method. (2)Through the analysising on density of leachate in observe wells,the density of leachate at different position have the following change law and trend with time:In the first two conditions with fracture and without fracture,the curves of density have rising and decline stages with time,and the density of leachate will tend towards stability after 15 years;Far from the landfill site and the border of study district,the density of leachate rise constantly,but the density value is very low,it can not cause danger for people's life and activity. The clay stratification with low permeability greatly reduced the level and vertical transportation,relatively the density has a serious hysteresis,and the density curve has rising stage all the time,but density value is very low all the time. (3)This text has simulated and predicted the range and degree of effect of leachate around the landfill. According to the simulation results,the range of effect is close relations to the permeability medium,the permeability is large, then the coverage is wide;The permeability is weak,then the coverage of leachate is small on the contrary;The fracture also has seriously influence on the distribution of leachate coverage,on the fracture site,the vertical effective range will expand,and the effective degree is weakened on the level plain. After covering,effective range and degree in landfill are smaller than the first two situations. (4)Through simulation and analyzing the simulation result,it is verified that the proceeding renovate project in Qilong landfill is effectual and in time.
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