Investigation Laboratory Simulation Of DNAPL Pollution Process In Heterogeneous Porous Media

In recently years,the petrochemical industry and its related industries and transportation industry have developed rapidly,and it also produces more and more serious pollution.The slightly soluble petroleum contaminants,which is often called Non-aqueous phase liquids in our research(its English name is:Non-Aqueous Phase Liquid,Abbreviated as NAPL).And the Dense Non-Aqueous Phase Liquid(its English name is:Dense Non-Aqueous Phase Liquids Abbreviated as DNAPL)means the part of a non-aqueous liquid with a greater density than water.If a leak occurred during use or transit which would lead to the groundwater and soil pollution,and also would bring great harm to human survival environment.Therefore,research on DNAPL migration and distribution,monitoring methods and management methods,has become the advanced subject in the field of groundwater environment.In this paper,we mainly studied the influence of the interface of porous media on the migration process of DNAPL.Through the establishment of two-dimensional sand tank simulation experiment,the size of the experimental device was 80cm length,3cm width and60cm height.From top to bottom,the fine sand with particle size of 0.16-0.315mm 0.315-0.45mm medium sand,0.45-0.9mm coarse sand,0.9-4mm gravel and boulders larger than4mm were used.The migration process of DNAPL in layered porous media were observed by digital camera,the migration characteristics and regularity of the non-saturated porous media in the layered porous medium,and the characteristics of the residual DNAPL in the saturated state were observed,and plot the frontal curve of the DNAPL migration process in the unsaturated state,the frontal curve of DNAPL migration in unsaturated state was plotted and the effect of porous media interface on DNAPL migration was discussed by image analysis.Under the unsaturated state of DNAPL infiltration test,the pollutant injection rate was2.08ml/min,totally injected 500ml.The results of infiltration test of pollutants in layered porous media showed that the process of DNAPL pollutant infiltration was mainly affected by gravity force.As the particle size of each layer was gradually reduced from top to bottom,which leaded to the pore in the medium of the lower layer was larger than the pore of the upper layer.Therefore,DNAPL downward migration speed faster and faster,so the migration of the DNAPL at the interface of the porous medium was mainly horizontal diffusion.The migration of remaining DNAPL in saturated porous medium test,the water injection speed was 0.83ml/s,the water injection time was 120min,and 1.44*10~4 ml water was injected into the saturated medium.The results of the migration test of the pollutants in the layered porous medium showed that after the water was injected,with the rise of water level,DNAPL gradually penetrated into the layered porous media.The color of the DNAPL stained with Sudan red was faded,and the pollution range increased,and the red floc remained on the surface of the granite.The small red floc in the fine sand medium with larger particle size was larger than the medium sand,coarse sand and other medium with large particle size.In this study,the method of high density resistivity will be used,through the establishment of a two-dimensional sand tank model indoors,and will carry out the infiltration test on the migration and distribution of dense non-aqueous phase liquid pollutants in heterogeneous porous media.Non-aqueous liquid pollutants infiltration and distribution,while the use of high-density resistors collected infiltration test process of sand points at all points of the data,import the collected data at the same time into the surfer software,drawing the resistivity distribution at each time during the experiment,and the resistivity distribution of each time will be analyzed and discussed.The characteristics of resistivity change during the migration of heavy non-aqueous liquid pollutants in heterogeneous porous media are discussed,and the migration and distribution characteristics of pollutants are obtained.The test was carried out under the condition of stable water level,and 500mL of dense non-aqueous phase liquid pollutants with reddish red dye were injected at a rate of 2mL/min,the results of the infiltration test of pollutants in layered heterogeneous porous media showed that the non-aqueous phase liquid pollutants are not only affected by gravity but also by capillary force during the infiltration process,and there is a low resistance anomaly,the resistivity is between0~200?·m,and the larger the pollutant infiltration,the smaller the resistivity value is.The pollutants are mainly migrated vertically during the infiltration process and will form a transport channel in the vertical direction.The pollutants migrate from the transport channel to the bottom of the sand tank and accumulate at the bottom of the sand tank.Through the of distribution of resistivity of heavy non-aqueous phase liquid pollutants in the sand trough space during infiltration test can be seen that the change of resistivity value is related to the migration process and distribution range of dense non-aqueous phase liquid pollutants,and the resistivity distribution of dense non-aqueous phase liquid pollutants in the sand chamber space.The resistivity profile can clearly show the changes in the contaminants in the various areas of the sand tank,thus clarifying the extent of pollution range and the degree of pollution.