Water Quality Evaluation And Anti Pollution Performance Of Shallow Groundwater In Jinta Basin

Jinta basin is located in the middle and lower part of Hexi Corridor in northwest Gansu Province.It belongs to the middle and lower reaches of Heihe River Basin.There is no self-produced surface water,and rainfall is rare.Domestic water and agricultural production water are mainly from groundwater exploitation.This paper relies on the project of "1:50000 hydrogeological survey of Heihe River Basin in Hexi Corridor" of hydrogeological environmental geological survey center of China Geological Survey Bureau.According to 192 groups of groundwater sample data and hydrogeological data collected,this paper describes the characteristics of groundwater hydrochemistry distribution in Jinta basin,draws the distribution map of groundwater hydrochemistry types,evaluates groundwater quality in Jinta basin with single index cvaluation method and improved fuzzy comprehensive evaluation method,draws the distribution map of each index content and the results of fuzzy comprehensive evaluation Distribution map;evaluate the inherent anti pollution performance of Jinta basin by using the drastic model,draw the distribution map of the inherent anti pollution performance of groundwater;The evaluation system of special anti pollution performance of groundwater is constructed,the weight of each index is determined by AHP,and the corresponding distribution chart of evaluation results is drawn.The main conclusions are as follows:(1)The pH value of groundwater in the study area is between 7.19-8.91,which is mainly weakly alkaline,and the spatial variation of the pH value of groundwater is relatively small and basically stable.There is a relationship between Na+>Mg2+>Ca2+>K+in the cation concentration and SO42>HCO3->Cl->NO3-in the anion concentration.The hydrochemical types of shallow groundwater in the study area are mainly SO4—Mg type,SO4—Mg·Na type,SO4 · HCO3—Na·Mg type,SO4 · Cl—Na·Mg type.(2)The results of single index evaluation method show that the main indexes affecting the quality of groundwater are total hardness,TDS,sulfate,chloride,sodium and nitrate.The results of the improved fuzzy comprehensive evaluation method show that there are 89 groups of class V water sample points in Jinta basin,accounting for 46.35%of the total number of water sample points;54 groups of class IV water sample points,accounting for 28.13%of the total number of water sample points;17 groups of class II water sample points,accounting for 8.85%of the total number of water sample points;32 groups of class III water sample points,accounting for 16.67%of the total number of water sample points;no class I water distribution is found.(3)According to the evaluation of the inherent antifouling performance of the research area by the drastic model,the results show that the overall antifouling performance of groundwater in the Jinta basin is good,and the area with medium antifouling performance has the largest distribution area,mainly distributed in the west of the basin,the Middle East Town and the area near Dazhuangzi township.(4)The evaluation system of special anti pollution performance is constructed,the weight of each index is determined by AHP,and the anti pollution performance of groundwater under the influence of human activities is calculated:the evaluation result is similar to the result of inherent anti pollution performance,and the overall anti pollution performance of groundwater is better.