Resistivity Imaging Of The Migration Process Of Heavy Organic Pollutants In Fractured Rock Mass

In recent years,the prevention and control of pollution in the groundwater environment has mainly focused on the research and treatment of groundwater non-aqueous organic pollutants(NAPL),especially the heavy non-aqueous organic pollutants(DNAPL)that are heavier than water.Because DNAPL is easy to deposit and accumulate in groundwater environment,and it is difficult to clean up.At this stage,most of the DNAPL researches are indoor porous media migration model experiments such as sandboxes,and the research in rock fissures has not been reported yet.In order to study the migration mechanism and distribution characteristics of DNAPL in fractured rock media,this paper establishes a carbonate rock and sandstone rock model with different fractures,and uses resistivity imaging to monitor DNAPL in carbonate rock and sandstone rock media.The migration process in space,the feasibility of the resistivity imaging method to monitor the migration of DNAPL in the rock medium containing fractures is discussed,and the resistivity images of DNAPL monitored in different types of fractured rock models are compared to analyze and discuss the fractures.The influence of existence and geophysical properties of the rock itself on the transport and distribution of pollutants.Electrical Resistivity Tomography(English name Electrical Resistivity Tomography,ERT for short)is a geophysical exploration method that uses the difference in resistivity values to monitor the properties of the medium.In this paper,the ERT method is used to monitor the DNAPL migration process in carbonate rock media containing parallel fractures and chevron-shaped fractures,sandstone rock media containing "chuan"-shaped fractures and "X"-shaped fractures,and study the differences in the same rock medium.The influence of the crack shape on the migration and distribution of DNAPL in rocks.The study found that in the same rock medium,the migration of DNAPL in the rock is roughly similar,but the distribution is obviously affected by the shape of the cracks.During the experiment of carbonate rock,the rock resistivity of parallel fractures increased from 1300Ω·m to 3500Ω·m,and the main area of increase was the right side of the rock fracture;the herringbone fractures increased from 5000Ω·m to 3500Ω·m.7500Ω·m,the main area of increase is the left side of the rock fissures,which are the exit positions of the fissures in the rock medium,indicating that in the rock medium with poor permeability such as carbonate rocks,DNAPL will follow the shape of the fissures.Perform the migration.In the experiment of sandstone rock,the relative resistivity of the rock with the "chuan"-shaped fracture increased from 51Ω·m to90Ω·m,and the main increase was at the outlet of the fracture near the pollutant drip point;the cause of the "X"-shaped fracture 50Ω·m increased to 170Ω·m,mainly in the middle of the rock and the exit position of the crack.It can be seen that in the sandstone medium,DNAPL will also migrate with the shape of the crack,but compared to the carbonate rock medium,The migration of DNAPL in this kind of rock medium with better permeability is affected by gravity more significantly.Comparing the DNAPL migration experiments in the poorly permeable carbonate rock model with different fractures and the sandstone rock model with better permeability,consistent rules are obtained from the resistivity images,which is the ERT method for DNAPL in rocks with fractures Strong proof of the feasibility of monitoring the transport distribution in the medium.It is of practical significance to delineate the scope of DNAPL contamination from a quantitative point of view and to evaluate the degree of contamination.It has important application value for the determination of the DNAPL contaminated area in the field and the study of the migration mechanism of DNAPL in fractured media.