Determination Of Saturation And Permeability Coefficient Of DNAPL Contaminants In Saturated Sand

In recent years,the research and treatment of non-aqueous phase liquids(NAPL)in groundwater have become the focus task of the prevention and control of underground environmental pollution,of which the heavier than water is called heavy non-aqueous organic pollutants(DNAPL).Typical DNAPL include hydroelectricity,electroencephalography and Polychlorodiphenyls.In order to study the migration mechanism and distribution characteristic of DNAPL under actual environmental conditions,this paper used two different monitoring methods,image method and high-density resistivity imaging method,to monitor the drainage?water injection process and the migration and distribution characteristics of DNAPL in heterogeneous porous media in the indoor two-dimensional model.High-density resistivity imaging method was used to monitor the drainage and water injection process?the migration and distribution characteristics of DNAPL in heterogeneous porous media in the indoor three-dimensional model.According to the Archie formula and Kozeny-Carman formula,DNAPL saturation distribution map and DNAPL permeability coefficient in the 2D and 3D models were obtained.The test results in the 2D and 3D physical models had some similarities:when the groundwater level rose,the water level at the position of the clay lens produced a"concave"surface growth trend.The migration and diffusion directions of water and DNAPL tended to the location where the medium was loose,resulting in a dominant migration channel with faster migration speed.During the redistribution of DNAPL,the migration of DNAPL was mainly affected by the action of gravity.The contaminated area moved down,the content of DNAPL in the contaminated area decreased,and the relative value of resistivity decreased.However,due to the complexity of the three-dimensional groundwater environment,the water and DNAPL transport in the three-dimensional physical model had certain characteristics:during the drainage test in the three-dimensional model,the presence of the lens body blocked the amount of water contained in the medium above the lens body,which made the water in the medium above the lens body difficult to discharge;In the 3D model,DNAPL contaminants were preferentially transported to the area where the lens was located at a lower position.The relative resistivity values on the lower position were 80?·m and 55?·m,which were greater than the 48?·m and 10?·m on the other side.In the three-dimensional groundwater environment,the presence of the lens was not only affected the migration of water and DNAPL contaminants in the profile of the lens,but also had a similar effect the migration of water and DNAPL in the adjacent profile.The determination of saturation parameters and permeability coefficient parameters during the DNAPL injection test was of great significance for studying the transport characteristics of DNAPL contaminants.From the calculation results,the following conclusions can be drawn:the spatial distribution of saturation during the DNAPL injection was uneven and was greatly affected by the amount of DNAPL injection.When the DNAPL injection rate was large,the error between the DNAPL injection value estimated by the high-density resistivity data and the actual injection amount recorded by the experiment was relatively large,and the maximum error could reach 27.1%.But when the injection volume was small,the error between the estimated value and the actual injection volume was small,and the minimum error could be 0.03%..It proved that the high-density resistivity method was feasible in monitoring the saturation distribution of DNAPL pollutants in three-dimensional groundwater space and quantitative analysis.The smaller the particle size of the medium,the greater the porosity and the greater the capillary force on the water,the more difficult the infiltration process of DNAPL in saturated medium,and the lower the permeability coefficient and permeability of DNAPL contaminants..In this paper,the porosity of quartz sand medium with a median diameter of 0.750 mm is 0.202,which was greater than 0.2004 that was the porosity of quartz sand medium with a median diameter of0.812 mm.The permeability coefficient of DNAPL was 4.686×10~-44 m/s,which was less than5.359×10~-44 m/s of 3D models,permeability 2.685×10~-55 m~2was less than 3.07×10~-55 m~2 of 3D models.This paper provides an effective method for the determination of DNAPL saturation and permeability coefficient in contaminated areas.It is of great significance for understanding the transport mechanism and distribution characteristics of DNAPL,as well as determining the range and extent of pollution.