Effect of Concentrated Leachate Recirculation on Leachate Level and Slope Stability of Municipal Solid Waste Landfill

260 tons concentrated leachate per day is produced at the leachate treatment plant at Chang'an landfill,which is considered to be recirculated into the landfill of municipal solid wastes.The effect of leachate recirculation on the slope stability of the landfill should be evaluated.The results from engineering geology and hydrogeology survey were firstly presented.Three-dimensional unsaturated-saturated seepage analyses were carried out by using GMS software to predict the change of leachate level as a result of the leachate recirculation.Based on the leachate levels and pore-water pressures obtained from the seepage analyses,slope stability analyses were carried out to evaluate the safety of the landfill.Some control measures were proposed to eliminate the adverse effect of leachate recirculation on the landfill safety.The analyses indicate that the factor of safety(FS) for the landfill with the current leachate level is slightly greater than the safety requirement(FS=1.3),and the current leachate level happens to be the critical level.Direct leachate recirculation will result in a significant rise in leachate level,which will cause a significant decrease in the landfill safety.The landfill is likely to fail after a direct leachate recirculation.If the leachate recirculation is executed after the current leachate level is lowered down by 3 m and the resultant leachate level will be lower than the current leachate level,the landfill can remain safe.Vertical pumping wells are proposed to implement the drawdown work,and if 45 wells are used and pumping is conducfed for 3 mouths,the leachate level will decrease by 3 m,which meets the safety requirement.