Effects of inner heterogeneity on long-term DNAPL migration in porous media

Abstract

When dense nonaqueous phase liquid is released from human activities and infiltrates into groundwater system, its migration is influenced by heterogeneity of aquifer seriously. In this study, an experiment is conducted in two-dimensional heterogeneous translucent granular porous media to explore the long-term migration of perchloroethylene (PCE, 1,1,2,2-tetrachloroethene). Porosity of translucent porous media is derived by light transmission micro-tomography method. Afterward, a three-dimensional (3D) right square pyramid microstructure for granular media is developed to obtain the permeability and entry pressure. Representative elementary volume (REV) of translucent granular porous media is estimated using a criterion of relative gradient error ( $$\varepsilon_{\text{g}}^{i}$$ ). Based on the obtained heterogeneities of media and corresponding REV estimation, simulation models with consideration of inner heterogeneities of media and without consideration of inner heterogeneities are compared to reveal the simulation effects. The discretization of simulation region is conducted according to results of REV estimation. Compared with model without consideration of inner heterogeneities, the model based on inner heterogeneities is more capable of characterizing the migration of PCE and is in good agreement with the experiment during the entire long-term contaminant migration including calibration, verification and validation periods. Moreover, observed PCE infiltration and spreading behavior are validated through moment analysis. This study reveals the complexity of PCE behavior during long-term contaminant migration periods and the importance of quantification of media heterogeneity for accurate simulation. Simultaneously, 3D microstructures of porous media should be delineated effectively.