Study On The Identification Of Groundwater Pollution Risk Sources In Mi-Huai-Shun Area

In order to prevent and control groundwater pollution,it’s a key part to accurately identify the risk sources of groundwater pollution.In this study,taking Mi-Huai-Shun area of Beijing as an example,on the premise of full collection of basic data in the study area,the hydrochemical anomaly identification method and the pollution anomaly identification method were used to identify the abnormal data of various components in groundwater.Afterwards the abnormal area and the degree of abnormality were divided according to the abnormal data,then the land-use data and the distribution of potential pollution sources were combined to identify the risk sources.Eventually,the reduction coefficient was used to calculate the amount of total nitrogen（TN）that penetrated the vadose zone and reached the groundwater,and the correlation analysis between it and the concentration of ammonia,nitrite and nitrate confirmed the correctness of the groundwater pollution risk source identification result.The main conclusions of this thesis are as follows:（1）The groundwater chemistry type in Mi-Huai-Shun area was dominated by HCO₃-Ca type,with a small amount of HCO₃-Mg type and HCO₃-Na type.In general,the groundwater quality was good,withⅢclass groundwater accounting for 65.85%,whileⅣandⅤclasses accounting for 24.39%.Among the indicators participating in the groundwater quality assessment,NH₄⁺had the highest contribution ofⅣandⅤclasses groundwater,with a contribution rate of 70%.The hydrochemical anomaly identification method took into account the integrity of the groundwater chemical field,and used five hydrochemical maps combined with Mahalanobis distance to identify abnormal data.The pollution anomaly identification method mainly identified abnormal data for minor components and trace components.The anomaly identification results of the two methods were combined and classified.The third-level region with the highest degree of anomaly had a total area of 40.64 km²,located near the intersection of Chao and Bai river in the northeast of the study area and in the south-central study area;the area of the second-level region was 268.77 km²,mainly located on the east side of the study area;and the normal regions were located in the north-central and southwestern part of the study area.（2）The land-use distribution map and the result of anomaly identification were combined to calculate the coincidence degree,which found that the residential area in the comprehensive anomaly region（third-level region and second-level region）accounted for 67.12%of the total residential area,the agricultural area accounted 61.92%of the total agricultural area,and the sewage rivers accounted for 87.81%of the total sewage rivers.Therefore,it was believed that the agricultural area,residential area and the sewage river were the main risk sources of groundwater pollution in this study area.Subsequently,different risk sources judgment methods were set for different areas.In the third-level region,all agricultural areas,residential areas,sewage rivers and industries were considered to be groundwater pollution risk sources.In the second-level region,all agricultural areas,residential areas,and sewage rivers were pollution risk sources,meanwhile,the industries within the influence radius of groundwater sample point were considered to be the risk sources of groundwater pollution.In the normal area,only the industries near the detection points of trace components were regarded as the risk sources of groundwater pollution.（3）According to the results of groundwater pollution risk assessment,the reliability of the division of abnormal areas was verified.The proportion of units with medium to high pollution risk level in normal region,second-level region and third-level region was 69.29%,85.57%and90.63%.This research used TN load and the reduction coefficient of the vadose zone to calculate the TN penetration load,and analyzed the correlation between TN penetration load and the concentration of ammonia,nitrite and nitrate in the groundwater.The analysis results showed that the TN penetration load was correlated with the sum of ammonia,nitrite and nitrate,nitrate,and ammonia at the level of 0.01.Therefore,it was believed that the identification result of groundwater pollution risk sources by combining the hydrochemical anomaly identification method and pollution anomaly identification method has certain accuracy and persuasiveness.