Pore network and Darcy scale modelling of DNAPL remediation using ethanol flushing: Study of physical properties in DNAPL remediation.

Co-solvent flushing into contaminated soils is one of the most effective techniques for Dense Non-Aqueous Phase Liquid (DNAPL) remediation. In addition to the increase of DNAPL solubility, co-solvents (e.g. ethanol) can alter the viscosity and density of aqueous phase and diffusion coefficient of solute. Any changes in these parameters can change the flow behaviour and alter the upscaled DNAPL mass transfer coefficient which is a key parameter controlling soil and groundwater remediation at Darcy-scale. While numerous studies have investigated DNAPL remediation using co-solvents at the Darcy scale, pore-scale modelling of co-solvent enhanced DNAPL remediation has not been well investigated. In this work, a three-dimensional pore-network model was developed to simulate the 1,2-dichlorobenzene (DCB) remediation experiments using ethanol-water flushing solution. The model simulates the effect of changes in solubility, viscosity, density, and diffusion coefficient during co-solvent flushing of the DNAPL. The results of pore network modelling for ethanol-water flushing for the DCB remediation were also validated using the experimental data. In addition to pore-scale modelling, a continuum scale modelling (Darcy-scale) was used for the DCB remediation using ethanol-water flushing. The results of both pore network and continuum scale modelling demonstrated that the ethanol content and flushing velocity influence the interphase mass transfer and DNAPL dissolution process. The results indicated while the mass transfer coefficient decreased in the presence of ethanol, the process of NAPL remediation was improved due to the substantial increase of solubility in the presence of co-solvent. The large scale modelling showed that NAPL bank can be formed in the front of ethanol-water mixture flushing.