Study On Groundwater Quality And Pollution Risk Assessment Of Typical Mixed Land Area In Chengdu Plain

Jingyang district is located in the northeast of the western plain of Sichuan basin and the third subsidence zone of Xinhua system.The whole area is divided into two parts with big difference.The boundary of two parts is Mianyuan river.The east is hilly landform predominated by agricultural land.The west is plain,and located in the central city and the region of industrial.In the western plain area,wastes of urban residents,wastewater of industrial zones,and the abuse of fertilizers and pesticides in agricultural activities make the local groundwater extremely vulnerable to pollution.Therefore,there is an urgent need for groundwater quality assessment,groundwater pollution status assessment and pollution risk assessment in the western plain area,so as to provide safety guarantee for local residents’ domestic water use.Groundwater pollution prevention and control plan could be formulated based on the assessment conclusions,provide scientific basis and favorable conditions for rational development and utilization of groundwater resources.In this paper,the groundwater environment in the western plain area of Jingyang district is taken as the research object,and the hydrogeological conditions and groundwater quality status of the research area are determined by site reconnaissance,sampling and monitoring and relevant data collection.The groundwater in the study area was assessed in terms of water quality,pollution status and pollution risk.Specific research methods and results are as follows:(1)Hydrogeological data and the distribution of pollution sources in the research area are collected through on-site reconnaissance and investigate.The groundwater quality in the study area was sampled and analyzed.(2)According to the test results of groundwater samples,F-value method and grey relational degree method were used to evaluate the groundwater quality in the study area.Results show that the study area overall water quality is poor.Most areas are classified as class IV water bodies,and some areas are classified as class III and class V water bodies.The exceeding index are nitrite,total hardness,ammonia nitrogen and manganese.The exceeding rate of total hardness and ammonia nitrogen was as high as 61% and 75%.(3)The results of water quality analysis in the study area in the last century were selected as the reference value.The improved single-index pollution index method was used to evaluate the groundwater pollution in the study area.The results show that groundwater pollution in the study area is mainly classified as medium polluted level and heavy polluted level,accounting for more than 60%.The pollution indexes are nitrite,total hardness,ammonia nitrogen and manganese,which are mainly distributed in Tianyuan town,Xiaoquan town and Deyang city in the west of the study area.(4)The assessment of groundwater pollution risk is mainly based on groundwater vulnerability,and factors of groundwater pollution load and groundwater functional value are considered comprehensively.An additional index of land use type was imputed into traditional groundwater vulnerability evaluation model,which includes 7indicators,Depth to groundwater(D),Net Recharge(R),Aquifer media(A),Soil media(S),Topography(T),Impact of the vadose zone media(I),Conductivity(C).Based on the land use of the study area,the pollution load is evaluated in combination with the degree of groundwater pollution.The groundwater storage in the research area was taken as the main factor,and the groundwater functional value was evaluated by taking into account the ecological sensitivity of groundwater,groundwater quality and other secondary factors.The scores of the above indexes were determined according to the expert scoring method combined with the actual situation of the research area,and the weight of each index was determined by the entropy weight method.Based on the above evaluation results,it is concluded that the areas with low risk of groundwater pollution in the study area are located in the areas of Bolong,Dexin and Xiaogan,accounting for about 24% of the total area of the study area.Groundwater pollution risk higher and higher in the study area and areas are mainly distributed in have been leakaged by continous and far the river Banks of the river floodplain Ⅰ level terrace,both accounts for about 25% of the area in the study area.(5)On the basis of the weight calculation method,python is used to design the weight calculation system interface of groundwater pollution risk assessment index.Subsequent similar regional risk assessment can make the assessment process more efficiently and conveniently.