| Chlorinated hydrocarbons are widely used industrially owing to their special properties.Due to improper disposal,running,emitting,dripping and leaking of the chlorinated hydrocarbons in the use process,which lead them to enter the groundwater system through various ways.This study takes the eastern urban area of Jinan as the research object,and the area of the study area is about 130 km2.There are many large-scale industrial enterprises in this area.Chlorinated hydrocarbons are widely used as raw materials and intermediates in the production process.Karst groundwater aquifers are widely distributed in the study area and Karst groundwater is the main source of water supply.The results of water quality monitoring in the source area wells show that there are many kinds of chlorinated hydrocarbons detected in Karst groundwater,which is seriously polluted.It is urgent to study the distribution characteristics as well as the migration and transformation of chlorinated hydrocarbons in groundwater,especially in karst groundwater aquifers.Therefore,simulating the migration and transformation of chlorinated hydrocarbons and predicting the development trend of chlorinated hydrocarbons pollution in karst groundwater can provide fundamental basis for the treatment of chlorinated hydrocarbons pollution in groundwater.In this study,hydrogeological and environmental geology survey,collection and analysis of water and soil samples,laboratory experiments and numerical simulation were used to analyze the spatial distribution characteristics of chlorinated hydrocarbons in groundwater system,including polluted pathways,pollution sources and typical chlorinated hydrocarbons in Karst groundwater.Isothermal adsorption experiments and hydrochemical data analysis were carried out to study the adsorption and biodegradation of chlorinated hydrocarbons in groundwater system.HYDRUS-1D is used to establish a one-dimensional vertical migration model of chlorinated hydrocarbons in the aerated zone to simulate their vertical migration in the aerated zone;GMS is used to establish a numerical model of groundwater flow and solute transport model in the study area to predict the development trend of carbon tetrachloride pollution plume;sensitivity analysis of the main parameters in the model is carried out to screen out more sensitive parameters.The research results are as follows:?1?The characteristics of groundwater aquifer system in the study area are systematically studied.The aquifer media types of groundwater system are Quaternary loose rock aquifer media and karst water aquifer media.Based on the data of atmospheric precipitation recharge and groundwater exploitation for many years,the characteristics of groundwater recharge,runoff,discharge,groundwater dynamic characteristics and influencing factors in the study area are analyzed.?2?The chlorinated hydrocarbons pollution sources in groundwater in the study area can be divided into four categories:chemical pollution sources,mechanical and electrical pollution sources,chemical fiber pollution sources as well as pesticide pollution sources.The main pollution ways are direct infiltration and lateral runoff of pollutants.The vertical distribution characteristics of chlorinated hydrocarbons in soil are related to lithology.Hydrus-1D simulation results show that the measured and simulated values fit well.Due to the different adsorption of chlorinated hydrocarbons in different media,the concentration of chlorinated hydrocarbons pollutants changes in a fluctuating manner from top to bottom.?3?The test results of chlorinated hydrocarbons components in karst groundwater show that carbon tetrachloride,trichloromethane,tetrachloroethylene,trichloroethylene,1,2,3-trichloropropane and so on are detected in the water samples,among which carbon tetrachloride is the most widely polluted,followed by trichloromethane.The detection rate of carbon tetrachloride in karst groundwater reached 74.4%,and the highest concentration reached 25.6?g/l.It was mainly distributed in the southeast of the study area.The extreme pollution concentration points were located in a chemical plant and a plastic test plant,respectively.The area of seriously polluted was 26.2 km2.?4?Isothermal adsorption experiments were carried out in different solid media.The experimental results show that the adsorption of carbon tetrachloride by limestone and silty clay conforms to Langmuir isothermal adsorption equation.The saturated adsorption capacity of silty clay is 3.466 mg/g,while in limestone is 2.0 mg/g,and the adsorption capacity of silty clay is higher than that of limestone.The hydrochemical response analysis of biodegradation of carbon tetrachloride in groundwater shows that the spatial distribution characteristics of various components confirm the existence of carbon tetrachloride.With biodegradation,the decay rate and biodegradation rate were calculated by first-order decay model,which were 0.00039d-1 and0.000154d-1,respectively.?5?Using MODFLOW module in GMS,a numerical model of groundwater flow in the study area is established,which is a three-dimensional heterogeneous anisotropic unsteady flow groundwater system.According to the actual groundwater flow field and groundwater level dynamic data,the model is identified and validated,and the hydrogeological parameters after recognition are obtained.The simulation results show that the groundwater flow field is well fitted,which can reflect the actual groundwater flow field characteristics;the fitting effect of the water level of the long-time monitoring wells is good,and the average error value of the water level fitting is within 0.5 m,which can reflect the dynamic change characteristics of the water level;analysis of groundwater balance shows that the groundwater in the simulation period is in a positive balance,with an annual equilibrium of 1950,000 m3/year.?6?The carbon tetrachloride was selected as the target pollutant,and the solute transport model was established to simulate the migration and transformation of carbon tetrachloride in the karst water aquifer.The simulation results show that the relative error between the simulated and measured values of the four monitoring points is controlled within 20%,and the simulation effect is better.The pollution trend of chlorinated hydrocarbons in groundwater is predicted.The prediction results show that due to the influence of adsorption and biodegradation,the concentration of carbon tetrachloride in the process of migration is gradually decreasing,which is consistent with the first-order attenuation model.The upstream pollution plume concentration is the most attenuated.Sensitivity analysis of the model shows that the most sensitive factors are biodegradability coefficient,partition coefficient and permeability coefficient. |
PDF Full Text Request