Numerical Simulation And Risk Assessment Of Groundwater Pollutants In A Strontium Mine In Southwest Karst Area

Over the years,groundwater environment has been deeply affected by human activities,and some areas are facing problems such as exhaustion of groundwater resources and deterioration of ecological environment.At the same time,karst area is a very fragile area of ecosystem,and groundwater system is more vulnerable to surface pollution.In order to reduce the adverse impact of waste water and ore produced during mining on groundwater environment.This paper,a strontium ore site located in Dazu karst area in western Chongqing was taken as an example,the current situation of groundwater environment quality in mining area through on-site investigation and collection of relevant hydrogeological data were analysed.Simultaneously,the groundwater flow model and solute transport model of Visual MODFLOW were established to predict the transport law of pollutants in aquifer after abnormal leakage of sewage pool in mining area.Finally,the pollution source load risk and the inherent vulnerability of groundwater in the mining area were evaluated to determine the risk level of groundwater pollution in the mining area.The conclusion would provide scientific theoretical basis for preventing potential groundwater pollution in mining areas.According to the data of groundwater samples in the study area,the chemical type of groundwater is mainly HCO₃—Ca type determined by Sukalev method.Using single factor method,typical Nemerow index method and improved Nemerow index method,a total of 12 general chemical pollution indexes and toxicological indexes were analyzed.It was concluded that the quality of underground water samples in the mining area reached Class III and better standards,and the results of improved Nemerow index method were more accurate.According to pollution-related analysis,groundwater quality was mainly affected by agricultural irrigation and residents'lives,while mining in the area mainly affects the quality of groundwater nearby.A numerical model of groundwater flow was established and plumbum and strontium,which were more harmful pollutants,were selected as solute transport simulation.According to the simulation,the polluted plume spread westward along the water flow under abnormal conditions in the Ganyantang mine,and finally migrated to the Longjing spring in the southwest of the downstream.According to the detection limit,the maximum migration distance of strontium reached 245.5 m on the 7300 day and reached Longjing spring,an ecological sensitive point,while the maximum migration distance of plumbum reached 155 m on the 7300 day and did not reach Longjing spring.During the simulation period,the contaminated plume from the crossroad mine mainly diffused around.The maximum migration distance of strontium was 102.5m on 7300 days,while the maximum migration distance of plumbum was83.5m on 7300 days.As it was far away from the residential area and there was no obvious ecological sensitive point around,the crossroad mine had relatively little abnormal pollution leakage to the surrounding environment.A comprehensive pollution risk assessment system based on the risk assessment model of pollution source load and the inherent vulnerability assessment model of groundwater in the process of strontium mining is established.At the same time,the analytic hierarchy process was used to determine the weight of each model evaluation index.The result shows that the risk of comprehensive groundwater pollution in mining area is medium risk.