Investigation on the influence of porous media interface on DNAPL migration based on image methods

The problem of dense nonaqueous phase liquid（DNAPL） polluting soil and groundwater has attracted extensive attention. The study of the transport characteristics of porous media with different particle sizes and their interfaces is the premise for determining the pollution area and repairing the groundwater environment. The effects of porous media interface on the migration and distribution of heavy non-aqueous liquids (DNAPL) are investigated by laboratory experiments. DNAPL infiltration experiment is conducted in a 2-D sand tank and pictures are taken to record the diffusion process using the digital camera. The image is processed with AutoCAD to draw DNAPL migration and the infiltration frontal variation pictures in different times are obtained. The results show that during the process of DNAPL infiltration, the migration is mainly controlled by gravity and capillary action. The capillary force decreased with the increasing particle size of the media, and the gravity plays a leading role in increasing the infiltration rate of the pollutants. The medium structure affects the migration pattern of DNAPL.The particle size of the medium increases layer by layer,the percolation area and the diffusion width of the DNAPL contaminant decrease layer by layer,the diffusion mode changes from planar to finger.When the interface structure is abrupt, the curvature of the DNAPL migration front line is correspondingly larger.At this time, the migration pattern of DNAPL exhibits a “convex” shape.In addition,different interfaces have different retention widths for lateral diffusion.As the particle size of the medium increases,the lateral diffusion width of the interface becomes relatively short. The results are of important practical significance for the evaluation of DNAPL contamination and the restoration of contaminated sites.