Analysis And Evaluation Of Groundwater Environment In Landfill Sites:Acase Study In Shigatse,Tibet

The way of municipal solid waste treatment and disposal is gradually changed to incineration,with the development of our country's economy and society,and the awareness of the disadvantages of landfill disposal in China.However,as the last pure land of our country and an important national ecological security barrier,according to the relevant investigation:landfill is the main way of disposal of municipal solid waste in the qinghai-tibet plateau.Landfill leachateLandfill leachate is a kind of organic wastewater with complex composition and high concentration formed,if it leaks into the groundwater aquifer and will pollute the groundwater quality,and the pollution will last for decades or more.Contaminated groundwater will also pose a higher risk to the health of the population.Therefore,this paper analyzes and evaluates the source pollution risk of landfill site,groundwater vulnerability,groundwater quality and residents'health risk on the basis of data collection,field investigation,sample collection and analysis,so as to provide scientific basis for landfill site management,pollution prevention and control and ensure the safety of groundwater.The assessment result of source pollution risk shows that the comprehensive pollution risk of the first pHase of Shigatse landfill is 5.5,which is medium pollution.The second pHase of the landfill is about to be put into operation,the comprehensive pollution risk is high?Ii=6.1?due to the higher water content of the fresh garbage,and the landfill volume increases?the improved collection and transportation efficiency of municipal solid waste in the landfill site of Shigatse city?.Several years later,the comprehensive pollution risk is gradually reduced,presenting moderate pollution.The groundwater vulnerability was analyzed and evaluated with DRASTIC model,the results show that:The groundwater aquifer in the study area has strong antifouling property,groundwater is less likely to be contaminated.A total of 19 conventional indicators including pH,total hardness,sulpHate,permanganate index,nitrate?N?,nitrite?N?,ammonia nitrogen,chromium?hexavalent?,fluoride,chloride,cadmium,lead,arsenic,zinc,selenium,cyanide,mercury,iron and total dissolved solids were selected for detection and analysis,the results showed that the main pollution factors of groundwater are ammonia nitrogen,hexavalent chromium and iron in the study area.In 2014,the groundwater quality of Shigatse landfill was relatively poor.Among them,the exceeding rate of ammonia nitrogen was 100%,and the maximum exceeding rate was 1.88 times.The hexavalent chromium exceeding rate was 33.3%,the maximum exceeding multiple was 1.08times;The iron excess rate was 66.6%,and the maximum excess multiple was 1.07times.In 2015,2017 and 2018,the water quality was relatively good,and only iron showed varying degrees of contamination.The exceeding rate and the maximum exceeding multiple were 100%,33.3%,100%,2.33,2.22 and 1.4 times respectively,other elements meet the groundwater quality?class standard?GB/T14848-2017?.In2016,every test indexes meet the groundwater quality of groundwater?class standard?GB/T14848-2017?.The groundwater quality in the study area is good,the water quality of each monitoring well is relatively stable,and it is generally shown as Background well>diffusion well>monitoring well.The groundwater quality of the region is relatively good in each water period,the water quality of each monitoring well is relatively stable,and the comprehensive water quality is good.The comprehensive water quality status in different water periods was dry season>level period>wet season.The pollution degree of water quality in each monitoring well was analyzed and evaluated for each year based on groundwater quality?class standard?GB/T14848-2017?as the background value,the results show that the comprehensive pollution of groundwater quality in 2014,2015 and 2018 was light pollution.In 2016and 2017,the comprehensive pollution status of regional groundwater quality was non-pollution.The pollution status of each monitoring well is background well>diffusion well>monitoring well>monitoring well in duolin substation,and the comprehensive water quality status in different water periods was wet season>level period>dry season.Health risk assessment results show that the carcinogenic and non-carcinogenic risks to women are significantly higher than the health risks to men.The carcinogenic risk caused by all exposure pathways is ranked as CR_cgw>CR_iov3>CR_dgw,the comprehensive carcinogenic risk of each carcinogenic factor by all exposure pathways is shown as Cd?1.645E-06?>Cr⁶⁺?6.679E-07?>As?4.041E-07?.The Non-carcinogenic risk caused by all exposure pathways is ranked as HQ_cgw>HQ_iov3>HQ_dgw,the comprehensive carcinogenic risk of each Non-carcinogenic factor by all exposure pathways is shown as CN^-?0.02418?>F^-?0.01657?>As?0.01295?>Cr⁶⁺?0.00633?>Cd?0.00388?>NO₃-N?0.00224?>Hg?0.00129?>NO₂-N?0.00037?>Zn?0.00017?.The risk control values of carcinogenic factors(Cr⁶⁺,Cd and As)were 0.05 mg/L,0.004mg/L and 0.01 mg/L.In order to ensure the safe drinking of groundwater in the landfill area and reduce the health hazard risk of surrounding residents,the risk control value of non-carcinogenic factors?NO₃-N?by all exposure pathways was 17.96 mg/L.In summary,The first p Hase of Shigatse landfill has little effect on groundwater.Because the first pHase of the site will be closed and the second pHase of the site is about to be put into operation.In order to ensure the safe operation of landfill and reduce the risk of groundwater pollution with the improvement of waste collection and transportation efficiency and the complexity of waste composition in Shigatse city,special attention should still be paid to landfill pollution sources and regional groundwater condition.According to the current situation of landfill pollution sources and regional groundwater pollution,effective methods and means will be actively adopted to strengthen landfill management,strengthen pollution source control,prevent pollution from spreading,and repair contaminated groundwater timely if necessary.