Study On Water Quality Evaluation Method And Groundwater Numerical Simulation In Western Chongqing

Groundwater is widely distributed and stable,and is less polluted than surface water.In the process of opening up and utilizing groundwater resources,prevention of pollution should be taken as the first priority.It is necessary not only to monitor the groundwater quality,but also to evaluate the groundwater quality comprehensively,timely and accurately,so as to provide scientific basis for taking preventive and protective measures.Different methods of groundwater quality assessment have different validity and rationality.This study chooses the western Chongqing area as the research area.Taking the sampling data of 34 monitoring wells in 2016 as an example,the groundwater quality comprehensive evaluation method,the improved Nemerow comprehensive index method and the fuzzy comprehensive evaluation method are selected to evaluate the groundwater quality.The results show that the comprehensive evaluation method of groundwater quality is simple and applicable,but it is easy to be affected by the maximum value,and it can not reflect the difference of water quality between monitoring wells with the same evaluation results;the improved Nemerow comprehensive index method can eliminate the influence of the maximum value to a certain extent,but it needs to optimize the calculation of the weight value;the fuzzy comprehensive evaluation method solves the problem of data continuity.But it can not reflect the impact of individual special indicators alone.Therefore,usethe improved Nemerow comprehensive index method as basic evaluation.Ratio of overIII-standard monitoring's proportion Oito the sum of O_i as weighting factor W_i',and at the same time eliminated background influence factor iron as the improved evaluation method suitable for Western Chongqing.The results show that in Western Chongqing 70.6%of the monitoring are over III-standard,and 29.4%of the monitoring are below III-standard.82.4%of the monitoring areover-III standard in Area 1,and 17.6%of the monitoring are below III-standard standardsin Area 1.In Area 2,58.8%of the monitoringareover III-standard in Area 2,and 41.2%of the monitoring are below III-standardin Area 2.Based on the results of groundwater quality evaluation and the principle of groundwater quality monitoring well layout,it is known that the main pollutant of groundwater in Liangba monitoring well is nitrite nitrogen,and the source of pollution should be river water invasion.Therefore,the Liangba monitoring well and its surrounding areas in Hechuan area are selected as the study area of groundwater numerical simulation,and the evaluation factor nitrite nitrogen is selected as the simulation factor.The change of nitrite nitrogen concentration with time in the process of river water pollution invasion is simulated.At the same time,the water quality of monitoring wells is evaluated by optimizing Nemerow comprehensive index method.The change of evaluation results with time coincides same as the change of nitrite nitrogen concentration with time.It shows that the improved evaluation method can evaluate groundwater quality timely and accurately.In view of the present situation of water quality in Western Chongqing,use the improved Nemerow comprehensive index method as basic evaluation,the ratio between theoverIII-standard monitoring's proportionsum of the proportionas Wi'andeliminated background influence factor iron in the same time as the improved evaluation method suitable for Western Chongqing.Make the results more realistic and objective.