Effect of salinity on DNAPL migration and distribution in saturated porous media

In this work the effect of salinity on the migration and distribution of DNAPL in saturated porous media was investigated. Tetrachloroethylene (PCE) was selected as the representative DNAPL (Dense Non-aqueous Phase liquid), and sodium chloride (NaCl) was used as the typical dissolved salt in groundwater. Batch experiments were first conducted to measure the contact angles and interfacial tensions (IFTs) of the NaCl solutions/PCE/quartz system. The results show that the contact angles of PCE decrease and IFTs between PCE and NaCl solution increase with the increasing concentration of NaCl, and the effects are more obvious at high concentrations of NaCl (>0.1 mol/L). Four 2-D flow cell experiments were then conducted, and the light transmission method was used to monitor the migration process of PCE and quantitatively measure the PCE saturation distribution in the porous media. The experimental results show that the increasing salinity in groundwater promotes the vertical migration of DNAPL, decreases the volumes of DNAPL entrapped along the migration path, and leads to the inclination of the migration path and pooled DNAPL towards the water flow direction. Moreover, in both homogeneous and heterogeneous (lenses) porous media, the horizontal and vertical spreading of DNAPL increases with the increasing salinity, resulting in a larger source-zone and the increasing PCE ganglia.