Prediction And Analysis On Remediation Effect Of Groundwater Pollution In A Chemical Plant

Groundwater resources have become one of the most important sources of water in the world,and it is particularly urgent to solve this problem because of the increasing amount of industrial,agricultural and human domestic wastewater discharges,which leads to more and more serious environmental problems in groundwater bodies.A small chemical plant in the southwestern part of a city discharges a large amount of untreated sewage into the groundwater body,thus causing many ecological problems such as soil and groundwater contamination in the plant and its surrounding area.The remediation of the contaminated groundwater area and the improvement of the environmental quality of the groundwater body are important elements of the subsequent groundwater management work in the area.The research object of this paper is a polluted underground diving system in a chemical plant and its surrounding areas.Through a series of work such as data collection,field investigation,drilling,geophysical prospecting,pumping test,seepage test,water sample collection and water quality detection,the scope and degree of groundwater pollution in the current research area are explored to determine the scope and degree of pollution in the current research area.Among the groundwater pollutants,carbon tetrachloride is the main characteristic pollutant,mainly concentrated in the former Wangsidian small chemical plant area and its southwest area.The characteristics of groundwater pollution in the study area are analyzed.The areas polluted by various organic pollutants in groundwater body in the study area are widespread and basically overlap with each other,mainly distributed in the small chemical plant and the downstream area of groundwater.Among them,the target pollutant carbon tetrachloride exceeded the standard multiple with the exceeding rate as high as 54.4%,which is the most serious pollution in the groundwater system of the whole research area.Cl~-means content is the highest in water chemical composition,the content is 177.15 mg/L.The chemical type of groundwater near the contaminated site is mainly Cl-Na·Ca type.The concentration of ions in groundwater is mainly influenced by the interaction between water and rock,and to some extent by evaporation concentration and human activities.In this paper,the MODFLOW module in the groundwater numerical simulation software GMS is used to establish the hydrogeological conceptual model of the research area,to generalize the model boundary and aquifer characteristics,to further establish the groundwater flow model by inputting the hydrogeological parameters obtained from the previous field experiments as well as the source and sink items of the model,and to identify and verify the model according to the measured water level values,and to adjust the model repeatedly until the model can better meet the actual conditions.Based on groundwater flow model,MT3DMS module was used to simulate carbon tetrachloride solute transport.The concentration of source intensity discharge was set at 552 mg/L,and the daily leakage of sewage was 0.5 m~3/d for 730 days.By analyzing the trend of pollutant transport,it is found that the carbon tetrachloride pollutant moves from northeast to southwest,and finally forms an elliptical contaminated area.The groundwater flow direction is the elliptical long axis.At the same time,the concentration of pollutant is significantly reduced downstream.Carbon tetrachloride organic pollution in groundwater is repaired by concentration zoning in the repair stage.In the first stage,extraction-treatment method is used to repair the highly polluted area.PRB permeability reaction wall technology is used as the second stage repair method.The repair process is simulated by MT3DMS module to observe the repair effect.The numerical simulation results show that the extraction-treatment method can reduce the total amount of pollutants,limit the diffusion of pollutants and reduce the pollution range.At the beginning of operation,the removal efficiency of pollutants is high,but the later effect is little.After 500 days of pumping,the maximum concentration of pollutants has been reduced to 0.89 mg/L.The PRB permeable reaction wall is used to repair low concentration pollution feathers,and the repair effect is better,and the range of low concentration pollution feathers is gradually reduced.At 4000 days of operation,the PRB system has achieved the expected repairing effect on pollutants(Class III water limit<2μg/L),which further indicates that the groundwater numerical simulation software can well reflect the repair effect.