Study On The Chlorine Hydrocarbon Pollution Characteristics And Hydraulic Control Mechanism Of Groundwater In The Eastern District Of A City

Most of the chlorinated hydrocarbon organic compounds are highly toxic,easily enriched,easily cause harm to human bodies,and even have carcinogenic,teratogenic and mutagenic effects.Since the reform and opening up in China,the continuous rise of industrial and mining enterprises has made chlorinated hydrocarbons used as a raw material for chemical and process manufacturing in large quantities.However,due to the inappropriate production processes and sewage discharge methods of some enterprises,a large number of chlorinated hydrocarbon compounds have entered the groundwater system,causing groundwater pollution and endangering human life.Therefore,it is urgent to control and repair the pollution of groundwater chlorinated hydrocarbons.This paper takes the eastern urban area of a city as a research area,where many chemical,manufacturing,and iron and steel enterprises are concentrated in the area.The chlorinated hydrocarbons used in its process manufacturing enter the fissure karst water aquifer of the groundwater system through different channels.The karst water pollution is serious.The simulation study on the hydraulic control of groundwater chlorinated hydrocarbon pollution in this research area can provide basic data basis for the control,restoration and protection of groundwater chlorinated hydrocarbon pollution.Based on the investigation and analysis of the basic conditions of regional geological structure,hydrogeology,meteorology and hydrology,and technological production of various industrial and mining enterprises,this paper collects groundwater chlorinated hydrocarbon water samples,detects the groundwater chlorinated hydrocarbon concentration,and resolves the groundwater chlorinated hydrocarbon pollution,Analyze and study the distribution rules of chlorinated hydrocarbons and typical chlorinated hydrocarbon pollutants in fractured karst water aquifers;use MODFLOW-96 module in software Visual MODFLOW to establish groundwater flow model,and use MT3DMS module to establish solute transport model to predict groundwater The migration trend of hydrocarbon generation pollution;taking the typical groundwater chlorinated hydrocarbon pollutant carbon tetrachloride?CCl₄?as the main treatment object,coupling numerical simulation with pumping well optimization,using MGO based on the water flow model and the solute transport model The optimization module establishes a pumping-processing technology repair method,optimizes the pumping well scheme,and determines the optimal pumping well location and pumping volume.This paper obtained the following research results:?1?Analysis of pollution sources of chlorinated hydrocarbons in groundwater.The absolute principal component analysis method is used to divide the groundwater chlorinated hydrocarbon pollution sources into four types:chemical industry,whose groundwater chlorinated hydrocarbons represent pollutants including carbon tetrachloride?CCl₄?,cis1,2-dichloroethylene?C₂H₂Cl₂?,and two Chloromethane?CH₂Cl₂?,trans-1,2-dichloroethylene?C₂H₂Cl₂?,chloroform?CHCl₃?,etc.contribute 50.81%to groundwater chlorinated hydrocarbon pollution;pesticides,whose groundwater chlorinated hydrocarbons represent pollutants Including 1,2,3-trichloropropane?C₃H₅Cl₃?,chlorobenzene?C₆H₅Cl?,etc.the contribution rate to groundwater chlorinated hydrocarbon pollution is 8.1%;for electromechanical,its groundwater chlorinated hydrocarbons represent pollutants including1,1,1-trichloroethane?C₂H₃Cl₃?,trichloroethylene?C₂HCl₃?,tetrachloroethylene?C₂Cl₄?,etc.,contribute 18.5%to groundwater chlorinated hydrocarbon pollution;chemical fiber,whose groundwater chlorinated hydrocarbons represent pollutants include1,1-Dichloroethylene?C₂H₂Cl₂?,1,2-dichloroethane?C₂H₄Cl₂?,etc.contributed 12.62%to groundwater chlorinated hydrocarbon pollution.?2?Distribution characteristics of groundwater chlorinated hydrocarbon pollutants.Analysis and detection of thirteen kinds of groundwater chlorinated hydrocarbon pollutants,including carbon tetrachloride?CCl₄?,trichloroethylene?C₂HCl₃?and tetrachloroethylene?C₂Cl₄?content have exceeded the standard.Carbon tetrachloride?CCl₄?and chloroform?CHCl₃?were selected as typical chlorinated hydrocarbon pollutants in groundwater in the study area,and ArcGIS 10.2 was used to draw the spatial distribution maps of the pollution of the two in the dry season,the flat water period and the high water period.To the east of the DW fault in the study area,carbon tetrachloride pollution plumes are concentrated near ZF,LJZ,PJY,and JG villages.The highest concentration of carbon tetrachloride is 30.2?g/L,which is located near a petrochemical plant south of LJZ village and west of the DW fault.The carbon tetrachloride pollution plume is mainly distributed near the villages of NW and SFZ.The concentration of carbon tetrachloride is below 6?g/L;the overall detection rate of chloroform concentration in groundwater in the study area is 69.77%during the year,and its concentration range is 1.52?23.7?g/L,the detection rate is relatively high,but it does not exceed the standard.The chloroform polluted plumes east of the DW fault are concentrated near the villages of LJZ,PJY,JG,and JX,and the chloroform polluted plumes west of the DW fault are mainly distributed.Near NWZ village,the spatial distribution of chloroform pollution concentration in groundwater is similar to the spatial distribution of carbon tetrachloride pollution concentration.?3?Fouling karst water chlorinated hydrocarbon pollution mechanism.In the exposed area of the Ordovician limestone in the study area,chlorinated hydrocarbon contaminants directly infiltrated into the fissured karst water aquifer,and migrated from south to north along with the groundwater runoff,causing chlorinated hydrocarbon pollution in the fissured karst water;The water level dropping funnel allows pore water contaminated with chlorinated hydrocarbons to enter the fissured karst water aquifer,resulting in chlorinated hydrocarbon pollution in the fissured karst water.?4?Establishment of groundwater flow model.The MODFLOW-96 module in the Visual MODFLOW software was used to construct a groundwater flow model in the study area.The groundwater flow system was generalized into a heterogeneous anisotropic three-dimensional flow.The fitting effect of groundwater flow field and groundwater level of observation wells shows that the simulation conditions are good and the simulation results are reasonable.?5?Establishment of solute transport model.Based on the groundwater flow model,using the MT3DMS module in Visual MODFLOW software,the solute transport simulation was carried out with the concentration distribution of groundwater carbon tetrachloride?CCl₄?in April 2018 as the initial concentration field,carbon tetrachloride?CCl₄?During the migration process,adsorption and degradation occur,and its pollution concentration and pollution distribution decrease year by year.However,the natural attenuation of groundwater causes the concentration of carbon tetrachloride in the groundwater in the study area to fall below the standard value,and the process is very slow.?6?Optimized scheme for hydraulic control of groundwater chlorinated hydrocarbons.Based on the groundwater flow model and the solute transport model,using the MGO module in Visual MODFLOW software,taking carbon tetrachloride as an example,a pumping-processing system for groundwater chlorinated hydrocarbon pollution control was designed,by changing its groundwater flow field,Hydraulic control optimization.According to the hydrogeological conditions of the study area,the pumping wells were optimized with a constant pumping volume.When the number of pumping wells was set to 4 and the treatment time was 1250 days,the total pumping volume was the smallest.Close to the carbon tetrachloride pollution center,the setting of the pumping well location is related to the distribution of pollution plumes and has nothing to do with the number of pumping wells.