Pollution Characteristics And Transport Simulation Research Of Polycyclic Aromatic Hydrocarbons In Soil And Groundwater In North China Plain

Polycyclic aromatic hydrocarbons?PAHs?have been listed as priority pollutant by the US Environmental Protection Agency as carcinogenic,teratogenic,and mutagenic persistent organic toxic chemical pollutants.Their impact on human health and the environment has attracted widespread attention worldwide.The North China Plain is an area where people gathering.The soil-groundwater pollution levels,pollution risks,and evolutionary trends are not yet clear.In this paper,a city area in the North China Plain is selected as the research area,and PAHs are the research object.The pollution level,pollution characteristics and human health risks of PAHs in soil and shallow groundwater of sampling survey have been analyzed.Three pollution scenarios,landfill leachate?point source?,river infiltration?Line source?and farmland infiltration?area source?,have been studied by established numerical model,in the soil and groundwater.Thus,the conceptual model of historical traceability,Pollution status and future migration of PAHs has been established.The main conclusions of the research are as follows:Both soil and groundwater in the North China Plain are contaminated with PAHs.The analysis results show that the total concentration of 16 PAHs in the surface soil of the study area is 1250.16?75192.64ng·g^-1,and which in shallow groundwater is 2.96?370.93 ng·L^-1;the risk assessment results show that the lifetime carcinogenic risk of PAHs in the surface soil is 6.01×10^-6?4.50×10^-3,which has higher risk.The shallow groundwater risk is 0.00?1.20×10^-5,which has potential risks;The results show that industrial discharge,traffic discharge and the large-scale use of fossil fuels are the main causes of pollution.By analyzing the hydrogeological conditions of three contaminated sites:point source?garbage landfill?,line source?sewage river?,and surface source?sewage irrigation farmland?,hydrogeological conceptual models were established,numerical models were established using Hydrus.The simulation results show that the transport of PAHs in the aerated zone soil is mainly controlled by the pollution source and the hydrogeological conditions of the site.The transport rate of PAHs is slow first,then fast and eventually stable over time.The trend of its penetration curve is similar,and the concentration distribution and penetration time of pollutants are different.If the pollution source cannot be effectively controlled,there is a risk of groundwater contamination.Through generalization of hydrogeological conditions in the study area,a conceptual model of hydrogeology was established,groundwater and solute transport models were established using GMS.The simulation results show that the transport of PAHs in shallow groundwater is mainly controlled by the groundwater system and pollution sources,pollutants diffuse into the groundwater centering on the source of pollution.The main direction of pollution diffusion is consistent with the flow direction of the groundwater.The scope of pollution continues to expand over time,the rate of diffusion of pollution halo gradually decreases,and the concentration of PAHs in contaminated groundwater continues to increase.