| With the continuous improvement of urbanization level and rapid economic development in China,the amount of solid waste generated is increasing day by day.As of 2018,China’s accumulated solid waste storage exceeded 60 billion tons,and a large part of the solid waste landfill lacks standardized and professional management and disposal,resulting in certain safety and environmental risks.In recent years,China’s management of solid waste landfills has gradually become standardized,but there is still a huge problem of legacy storage.In 2009,the sludge pit of the Xiapin landfill in Shenzhen experienced a pipe burst,causing downstream garbage body instability,resulting in a large amount of leachate and sludge leakage.Pollutants passed through the entire Futian and Luohu districts,and eventually reached the sea near Hong Kong,with a long-distance transport of up to 15 kilometers,causing large-scale environmental pollution along the way.Similar accidents of legacy solid waste landfills occur frequently in China,exposing management loopholes and reflecting the urgency and importance of risk control.The instability events of solid waste landfills are different from natural disasters such as landslides and mudslides.In addition to the possibility of instability and flow sliding causing building damage and personnel casualties,there may also be environmental pollution risks.The chain effect of instability-flow sliding-environmental pollution that arises may pose a greater threat to the population and ecological environment around the landfill.Although domestic and foreign scholars have conducted extensive research on the instability mechanism of solid waste landfills,there are still deficiencies in the disaster chain effect and risk assessment research after instability:(i)Most of the risk assessment systems are still in the qualitative-semi-quantitative stage,using risk matrices or empirical discrimination methods,lacking a quantitative disaster chain risk assessment system for individual objects;(ii)There is little research on the dual risks of safety and pollution caused by the instability of solid waste bodies.To address the shortcomings in existing research,based on the establishment of a national solid waste landfill disaster chain event basic information database,this paper clarified the main disaster-causing modes of the solid waste landfill disaster chain,and proposed qualitative and quantitative assessment methods for the dual risks of the solid waste landfill disaster chain.The main work and related achievements are as follows:(1)Through the identification of multi-source information and remote sensing images,a nationwide database of disaster chains in solid waste landfills has been constructed,which includes a total of 177 disaster chain events that occurred between 1957 and 2022.These events have resulted in a total of 950 deaths,with environmental pollution ranging from 2 kilometers to440 kilometers downstream.Additionally,this paper conducts statistical analysis on the spatial and temporal distribution patterns of disaster chain events,and summarizes the triggering factors and chain-disaster modes of solid waste disaster chains.The solid waste disaster chains in China are mainly concentrated in the Loess Plateau and the Southeastern Hill Region,and are most common in ten provinces including Shaanxi,Yunnan,Guangxi,Hunan,and Henan.The period from 2006 to 2008 had the highest number of disaster chains and deaths.Since 2008,the number of deaths caused by disaster chain events has been gradually decreasing.The types of solid waste disaster chain accidents can be divided into embankment self-collapse/instability and leakage of ancillary facilities(such as drainage pipes and overflow wells).Solid waste disaster chain events can be further classified into 13 chain-disaster modes,of which the most common are instability and flow-slide environmental pollution in the accumulation body and leakage-environmental pollution in the solid waste landfill.(2)Taking a typical solid waste landfill as an example,a safety and environmental risk investigation was conducted.Through processes such as drilling and sampling,testing and analysis,and indoor experiments,basic characteristics of the waste such as bulk density,moisture content,and shear strength were obtained.By conducting on-site monitoring,the long-term variation of water level in the landfill and the water quality of leachate were determined,and the pollution status of surrounding soil and water environments were evaluated.The results showed that there were significant differences in the characteristics of waste and leachate water quality at different locations and depths.Due to the high water level,it is necessary to pay attention to the drainage and discharge of leachate in the landfill,and the potential risk of instability caused by high water level.Although the concentrations of pollutants in the soil around and outside the landfill did not exceed the standard limits,the investigation found that the groundwater in the landfill area was contaminated,and the degree of pollution in the rock fissure water was lighter than that in the Quaternary strata water.The pollution was mainly concentrated near the regulating pool,and the biological indicators(total coliforms)downstream and at the mouth of the ditch in the landfill area were significantly polluted,with the excess multiple ranging from 11 to 260 times.The groundwater outside the landfill area was also contaminated,with more serious pollution in the Quaternary strata water than in the rock fissure water.The exceeded indicators were lead,ammonia nitrogen,CODMn,iron,manganese,1,2-dichloroethane,and total coliforms.The excess multiple of the samples ranges from 1 to more than 100.The surface water outside the landfill area was also polluted,with relatively consistent water quality pollution at 5 sampling points about1 kilometer downstream from the landfill.The samples with the exceeded multiple of 1-2 times accounted for 30%,2-10 times accounted for 26%,100-1000 times accounted for 9%,1000-2000 times accounted for 9%,and those exceeding 2000 times accounted for 26%.The test results showed that the fecal coliform and total coliform indicators in the river section along the mountainous river were severely polluted,while the pollution caused by ammonia nitrogen,permanganate index,and iron was relatively light.(3)Based on detailed on-site data and laboratory tests,considering the three elements of "source-pathway-receptor" risk,the Analytic Hierarchy Process(AHP)was used to construct a dual-risk assessment indicator system for the site hazard chain.The risk assessment is the goal layer,and hazard source identification,pathway evaluation,and sensitive target damage assessment are the criterion layers.Sixteen evaluation indicators were selected,and paired comparison matrices were established to obtain the weight values of each indicator.Based on the actual conditions of the site,each indicator was scored,and the risk index was calculated using the weighted sum method.The risk index was then compared with the risk level table to obtain the risk level classification result.By using the constructed evaluation indicator system,a risk level assessment was conducted on the typical municipal solid waste landfill site,and the result showed a medium risk level.This provides a basis for further quantitative risk assessment of the hazard chain.This qualitative evaluation system can be widely applied to other waste landfills and provide guidance for the comprehensive management and risk prevention of landfill sites.(4)A quantitative risk assessment method for the double risk of instability,flow-sliding,and environmental pollution in solid waste landfills considering parameter uncertainty is proposed.This method is used to quantitatively assess the potential instability and dam failure hazard chain of the typical municipal solid waste landfill.In the numerical simulation process,Geostudio software is used to conduct heap stability assessment,and the Monte Carlo simulation is used to calculate the probability of instability.Finally,the open-source mass flow simulation software r.avaflow is used to simulate the transport process of the unstable heap.In the hazard chain harm assessment,based on the results of numerical simulation and remote sensing image interpretation,the vulnerable body is identified,and the vulnerability of the vulnerable body is evaluated based on the evolution and spatial distribution of transport depth.The safety risk of the hazard chain is calculated.Using the F-N curve to evaluate the acceptable level of safety risk,the results show that the safety risk of the hazard chain is 0.176,far exceeding the unacceptable limit.This indicates that in the operation and management process of the landfill site,attention should be paid to changes in the leachate water level,stability of the heap and dam body,and necessary engineering measures should be taken in a timely manner.In addition,based on an environmental risk investigation of typical solid waste landfills,the human health risk of adult males,adult females,and children is evaluated,considering the groundwater and soil pollution caused by the landslide transport process.This paper focuses on the risk assessment of five heavy metal pollutants: Pb,Cd,Zn,Cr,and As.Soil ingestion and soil skin contact exposure pathways are the main analysis focus.The risk assessment results show that the overall non-carcinogenic risk and carcinogenic risk of the three groups of people under the hazard chain scenario have reached an unacceptable level,and the non-carcinogenic risk and carcinogenic risk are both higher in children than in adult females and adult males... |
