Research Of Groundwater Pollution And Vulnerability In The City Of Yulin And Its Surrounding Areas

In northern Shaanxi area, the precipitation is very little, the evaporation is intense and the surface water is scanty, therefore, the groundwater is the main source of production and life here. As the center of the energy and chemical base in northern Shanxi, Yulin and its surroundings areas are the concentration of residents living and the energe companies,at the same time agricultural and livestock production are more developed in this regions. Without properly handled of the significant amount of pollutants generated by industry, agriculture and residents, it will cause pollution to the limited groundwater resources, which is a serious threat to the safety of drinking of urban and rural residents and the people’s pHysical and mental health. Therefore, the study of groundwater contamination and vulnerability evaluation has theoretical value and practical significance to effectively prevent pollution,protect groundwater resources and guarantee residents’drinking water safety.This paper is based on the the research of northern Shaanxi urban groundwater pollution investigation and assessment from China Geological Survey Bureau. Taking the groundwater resource protection as the target and the shallow groundwater as the object,this paper studied on groundwater pollution and vulnerability evaluation systematically through data collection, pollution resource survey, sample collection and theoretic analysis.Based on the test data of54groundwater samples collected in the survey, using the single indicators evaluation method, Nemerow index and fuzzy mathematics method to evaluated the quality of groundwater. The results of single indicators evaluation method show that the over standard of Fe、Mn、TH、Mg2+is the main factor which affected the quality of groundwater. The results of Nemerow index and fuzzy mathematics are similar, while the latter is better in line with groundwater quality characteristics, the comprehensive compliance rate is87.0%. It shows that the water quality in this area is overall well. The results of groundwater pollution evaluation connected with environmental background value showed that both inorganic components and trace organic components presented pollution pHenomenon, among which the number of pollution samples of Mn、NO3--N、Fe、TH、TDS were the most, while the pollution class of Fe、Mn、NO3--N which were the main indexes resulting heavy pollution and very heavy pollution, were the highest. The pollution samples concentrated in Xiaojihan—Niujialiang town, the southern suburban of Yulin and Mahuangliang town.The pollution class of the groundwater quality exceeded point were all very heavy pollution, the reason of local groundwater quality getting worse was the human intense activity.This paper studied the relationship of all the composition with factor analysis. Taking the results of factor analysis as a guide, it analyzed the pollutants on the plane and the vertical distribution law combined with chemical properties of pollution components, the results showed that NO3--N、Cl-、TH were basically the same distribution in the plane, and they were mainly distributed in the suburban and towns where the human activities were intensive while the infrastructures were adequate; Fe、Mn were mainly distributed in the sandy beach and valley District with river and lake sedimentary facies. All of the pollution components were basically distributed in the groundwater where groundwater depth is less than20m, which reflected the character that they were apparently affected by human activities. It also summarized two processes of groundwater pollution in the study area.Referencing to the index and grading of DRASTIC,combined with geological and hydrogeological characteristics in the study area, we selected5factors which affected the vulnerability of groundwater:groundwater depth, rainfall infiltration coefficient, aquifer lithology, aquifer rich water and vadose zone lithology, and then superimposed and partitioned each layer boundary with GIS and generated independent blocks with a free boundary. All blocks were provided to Quantity Theory III model, and was classified in accordance with the calculation results, among of which, different categories represented different vulnerability partition. The vulnerability partition was in according to the distribution of COD which can represent the human factors. This indicated that the methodson based on GIS and third theory of quantification was of certain practicality and could be an effective method of groundwater vulnerability evaluation.