Groundwater Contamination Risk Assessment In The West Of Yili-river Valley Plain

This study area which is located in the west plain of Xinjiang Yili River Valley,including Huocheng and Qapqal County.The main river flowing through this study area is the Yili river.The weather condition in this area belongs to the arid and semi-arid climate characteristics.And the average rainfall per year is poor,but the evaporation is strong,which is geared to the water shortage area.Using overlay and index methods and process simulation method,the"static"and"dynamic"of groundwater pollution are studied,which is of great significance for the rational development,utilization and protection of water resources.Specific study results are as follows:（1）Using overlay and index method,this paper combined with the characteristics of the plain area of Yili River valley to evaluate the risk assessment of groundwater contamination.And the risk assessment of groundwater contamination which included three factors,the groundwater contamination load,groundwater intrinsic vulnerability,groundwater value.Analytic hierarchy process was applied to determine the weight of the three factors.Using the analytic hierarchy process to determine the weight value of three indicators were 0.57,0.33,0.1.The MapGIS6.7 software space analysis module was used to make the layer overlay.The result showed that:The area with relative low,medium,relative high of groundwater contamination area were1969.3km²,2216.69km²,731km².The highest proportion is the middle area.The pollution risk of higher level area were distributed in the alluvial fan,and the river upstream.（2）Using equilibrium method to calculated the groundwater flow in the study area.The results showed that:The total recharge of groundwater in the study area is 8.6233×10⁸ m³/a,and the total discharge is about 8.9614×10⁸m³/a,which is in a negative equilibrium state.The groundwater flow model was established by using Visual MODFLOW software.Based on the water flow model,the MT3DMS model was used to establish the solute transport model in the study area,and the variation trend of nitrate in groundwater was predicted in the next 30 years.（3）Nitrate was selected as the pollution factor in the study area.The initial concentration of nitrate was determined by the concentration of present situation in the groundwater.The supply concentration was determined according to the experience of irrigation fertilizing amount.The results showed that the range and concentration of nitrate pollution in groundwater are very small,and the scope of pollution is only 12km².The mainly nitrate pollution which are concentrated in the Yili River and near the county police,are the initial higher nitrate concentration.