| Landfill is the main means of disposal of hazardous waste at present,and the environmental risk of disposal is mainly caused by leachate leakage which may contaminate groundwater.Because of the obvious long-term,latent and irreversible influence of leachate leakage on groundwater,the research on groundwater environmental risk of hazardous waste landfill has attracted extensive attention in academia.Meanwhile,the risk management and control of groundwater pollution in the hazardous waste landfill should be more stringent in the karst region where pollution protection is weak.Based on the whole life cycle of landfill and the whole process management of pollution?source-path-acceptor?,this paper comprehensively identified the groundwater pollution risk source of hazardous waste landfill in karst fissure media.On this basis,a method of groundwater pollution risk assessment for hazardous waste landfill was established based on scenario analysis,and a case study of a hazardous waste landfill site in a karst fractured medium was conducted.From the point of view of source reduction and pollution path blocking,risk management suggestions and emergency measures for the prevention and control of groundwater pollution in landfill were put forward.The main results are as follows:?1?According to the groundwater pollution risk identification results of hazardous waste landfill,a groundwater pollution risk assessment method for hazardous waste landfill based on scenario analysis is established,which incorporates the LandSim-GMS coupling model to consider the uncertainty of the durability of final covering system,engineered barrier system and leachate drainage system and the influence of different closure and post-maintenance in the risk assessment of the groundwater pollution for landfill.?2?A hazardous waste landfill located in the south of China was chosen to conduct a case study based on the method mentioned above.During the 12-year operation period and 30 years after the closure,leachate leakage of the hazardous waste landfill will stay steady(25.47 L?d-1,confidence level of 95%).After that,due to the maintenance and management of landfill stop,a sharp rise of leachate head will lead to the increase the leakage volume,and reach a peak within 8a(435.90 L?d-1 at the peak,confidence level of 95%).According to of numerical modelling of groundwater flow and mass transport,the highest concentration of Cr6+ will reach 0.0087 mg?L-1 ten years later in scenario S2,lower than the natural background value of groundwater.It indicates the groundwater pollution risk of leachate leakage is relatively low.In scenario S3,The potential groundwater pollution risk caused by leachate leakage is grave with the highest concentration of Cr6+ reaching 0.329 mg?L-1,exceeded 3.29 times compared with the ? grade of Groundwater Quality Standard.?3?In order to reduce leachate leakage,leakage and contaminant transport through composite liners in typical hazardous waste landfill were predicted.The results show that the leakage rate may be influenced by the interface properties,the leachate level and the defect types.When the hole density of composite liners is 20 holes·hm-2,the maximum leakage rate through composite liners with circle defect having a radius of 5.6 mm is 22.7 m3·a-1·hm-2 When the length of defective seam on unit area is 200 m·hm-2,the maximum leakage rate through composite liners with defective seam is 42.5 m3·a-1·hm-2.The longest and shortest breakthrough time of composite liners with defects for Cd2+,which is taken as contamination indicator of heavy metal,are 2.74 a and 1.38 a respectively.By changing the properties of the underlying soil layer or increasing the thickness of the soil layer,the breakthrough time of contaminant can be delayed.?4?When leachate leakage happened or pollutants in leachate have caused groundwater pollution,the technology of hydraulic interception and vertical seepage can be used to block the pollution pathway to control the pollution plume.The problem of surface subsidence caused by pumping water should be emphasized in the placement of pumping wells. |
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