Modeling volatilization of residual VOCs in unsaturated zones: A moving boundary problem

► A model is developed to predict the migration of evaporation front from residual NAPLs in soils. ► The initial NAPLs affect the evaporation front location and mole fraction distributions in soils. ► The migration distance of evaporation front of NAPL is proportional to the square root of volatilization time. ► The NAPL phase will vaporize to gas phase and vanishes slowly as the time increases.