Study On The Chlorinated Hydrocarbon Migration Mechanism And Pollution Control Of Groundwater System In The Eastern Area Of A City

Chlorinated hydrocarbon is a common organic pollutant with a variety of harmful characteristics,which will pollute the groundwater environment and cause serious impact on the daily production and life of human beings.Chlorinated hydrocarbon pollution,as a social environmental problem that can not be ignored,has been widely concerned.The groundwater in the eastern urban area of a city is seriously polluted by chlorinated hydrocarbons.Therefore,it is necessary to carry out research on the migration mechanism and pollution control of chlorinated hydrocarbons in the groundwater in this area.This paper takes the eastern urban area of a city as the main research area,investigated the hydrogeological conditions,and the region groundwater samples,analytical characteristics of chlorinated hydrocarbon pollution distribution,and the pollution of chlorinated hydrocarbon sources,combined with the main factors influencing the groundwater pollution in the region,using GMS10.4 numerical simulation software,selection of carbon tetrachloride as the characteristics of pollutants in chlorinated hydrocarbon migration mechanism of pollutants in the groundwater system are numerically simulated,by predicting the migration of the pollution plume,the pollution migration law of chlorinated hydrocarbons in groundwater was clarified.Finally,taking the carbon pollution plume of tetrachloride in the hydrogeological section where a chemical plant is located in the eastern part of the study area as the research object,the optimization study of the chlorine hydrocarbon pollution control in the groundwater system was carried out,and the optimal plan of the chlorine hydrocarbon pollution control in the groundwater system was obtained.The main conclusions of this paper are as follows:（1）Pollution characteristics of chlorinated hydrocarbons in groundwater systems.Thirteen kinds of chlorinated hydrocarbon pollutants,including carbon tetrachloride（CCl₄）,were detected in 32 groundwater sampling sites in the study area.The pollutant with the highest detection rate was carbon tetrachloride（CCl₄）,the detection rate was 75%,and the detection concentration was between 0.30μg/L and30.2μg/L.The distribution map of carbon tetrachloride concentration of typical chlorinated hydrocarbon pollutants in groundwater was drawn by the Kriging interpolation method of Arc Gis software.The results showed that the deep karst fissure water in other areas was generally polluted by chlorinated hydrocarbon to different degrees except for the water quality in the groundwater recharge area in the southeast of the study area.The overall distribution of chlorinated hydrocarbon pollution in groundwater is a north-south banded distribution,and the polluted areas are mainly located in the northern part of the central part of the study area.The pollution center of carbon tetrachloride pollutants appears at the point W26.The detected concentration is 25.60μg/L,exceeding the standard 12.8 times.The pollution is very serious.（2）Numerical model of groundwater flows in the study area.According to the study area actual hydrogeological conditions,groundwater flow model is established using GMS10.4 numerical simulation software,and to simulate the flow field and the concept of a long hole to match with the measured values of the groundwater table,the simulation results show that long hole water process line fitting effect is good,four long view hole fitting error of the mean water level control within 20%,conform to the requirements of the model accuracy,within a certain error range can reflect the characteristics of the groundwater flow field in the study area and the changing characteristics of the groundwater table.（3）Study on the mechanism of chlorinated hydrocarbon migration in the groundwater system in the study area.Based on the groundwater flow model in the study area the comprehensive analysis of the groundwater system main chlorinated hydrocarbon component and spatial distribution characteristics,selection of carbon tetrachloride as the goal pollutant,carbon tetrachloride migration into groundwater system model is established,the pollution of carbon tetrachloride in the study area is relatively typical sampling well point pollutant concentration in the simulated values and measured values of the match,relative errors are within 20%,the fitting results are good,the model can reflect the changing tendency of carbon tetrachloride.Using the solute transport models built by pollutants to carbon tetrachloride in 10-year and20-year simulation prediction,we found that under the condition of hydrogeology in the study area,over time,carbon tetrachloride in the study area of plume the attenuation trend,on the whole,the pollution plume development along the groundwater flow direction from south to north.However,the area of carbon tetrachloride pollution plume still has little change,because it is difficult for carbon tetrachloride to reduce the pollution concentration to the standard limit through natural attenuation in the groundwater system,and the groundwater chlorinated hydrocarbon pollution will still cause serious impact.（4）Study on the control method of chlorinated hydrocarbon pollutants in the groundwater system.Under natural conditions,when the ground carbon tetrachloride average pollutant concentration to achieve governance concentration 2.0μg/L,the time of 16775d,with the passage of time,the plume area is reduced,the pollutants from the central and southern area northwest gradually migration,consistent with the mainstream of the groundwater flow direction,conform to the groundwater pollutant diffusion theory.When pumping well control is carried out,it is optimized through the MGO module in Visual Modflow.The results show that the layout of the eight pumping Wells is more in line with the optimization requirements for the control of chlorinated hydrocarbon pollution in groundwater at the research site,and the locations of the pumping Wells are roughly along the central axis and vertical direction of the carbon tetrachloride pollution plume,and close to the pollution source in the research site.The optimal pumping water is 55171m³/d.From the perspective of treatment time,the total amount of pumping water of 8 pumping wells was the minimum,the optimal pumping water was 53648m³/d,and the total pumping water was 53648386m³under the condition of treatment time of 1000d.When combined with pumping well and injection well,the optimization results show that,compared with no additional injection wells,the pumping efficiency of pumping well required to achieve the target pollutant concentration in the study site at the same time is significantly improved,and the optimal pumping water volume is significantly reduced compared with the pumping water volume with only 8 pumping wells.Therefore,injection well can improve the pollution control ability of pumping well.Among them,8 pumping and 5 injection wells layout method is the optimal control scheme in this study.When treatment time is 1000d,the optimal pumping water volume is 47288m³/d,and the optimal injection water volume is 19548m³/d.（5）Study on the optimization results of chlorinated hydrocarbon pollutant control in groundwater system.Compared with the pollution control system with only8 pumping Wells,the distribution method of 8-pumping and 5-injecting pollution control method has significantly better control effect of chlorinated hydrocarbon pollution in groundwater.Compared with the system with 8-pumping Wells,the optimal pumping water volume in a single day is reduced by 6360m³,the pumping efficiency is increased by 12%,and the chlorinated hydrocarbon pollution plume area after control is the smallest.The carbon tetrachloride pollutants are centered on the pumping/injection well and spread around.Therefore,taking the concentration of carbon tetrachloride in groundwater as the control target limit value of 2.0μg/L,the combined control scheme of 8 pumping and 5 pumping was adopted.The control time was 1187d,the total amount of pumping water was 56130856m³,and the total amount of water injection was 23203476m³.Under the condition of the limit of 2.0μg/L of carbon tetrachloride in theⅢclass of groundwater,all the carbon tetrachloride pollution in the groundwater reached the standard.