Precise simulation of long-term DNAPL migration in heterogeneous porous media based on light transmission micro-tomography

Abstract

Predicting long-term migration of dense non-aqueous phase liquids (DNAPLs) in subsurface systems is essential to determine appropriate remediation design for cleanup of subsurface contamination. The migration of DNAPLs is not only affected by the heterogeneity of porous media, but also controlled by the relative permeability of DNAPLs over long-term periods. A new light transmission micro-tomography (LTM) is developed to quantify the heterogeneity parameters including porosity, permeability and entry pressure of two dimensional (2D) porous media. Also, a relative permeability-saturation model (RPM) is proposed for the complexity of long-term DNAPLs migration in porous media, in which the infiltration and redistribution periods are simulated by the drainage and imbibition stages using Brooks and Corey (BC) model, respectively. To verify the effect of LTM and RPM, an experiment of long-term perchloroethylene (PCE) migration is performed in a 2D bench-scale sandbox and the simulation based on LTM and RPM is conducted to predict PCE migration behavior. Comparison and moment analysis of PCE plumes shows that PCE infiltration and spreading behavior is well modeled over long-term contaminant migration period including calibration, verification and validation periods. This reveals the complexity of DNAPL behavior and steps forward to accurately quantify micro-structures of porous media.