Multiscale Reductions in Mass Flux as a Function of Residual Saturation

Remediation strategies for reducing nonaqueous phase liquid (NAPL) mass have in many cases has been successful in removing significant portions of the contaminant mass originally present in the system. However, significant reductions in entrapped NAPL mass may not lead to sufficiently low mass fluxes from the source zone to meet remediation goals in the short-time limit. We consider source zone mass flux as a function of NAPL residual saturation for systems ranging from small scale laboratory studies to a pilot scale field investigation. We compare the residual saturation source zone mass flux relationship across this wide range of scales and compare to other observations made in the literature. We make predictions of the laboratory experiments based upon pore-scale modeling using only the grain size distribution, porosity, and NAPL characteristics as input. We simulate the velocity field using Lattice Boltzmann methods and model the dissolution process using high resolution numerical methods at the pore scale. We compare the simulation results with multiscale experimental observations and show the importance of NAPL morphology. We also comment on both the benefits and potential shortcomings of active NAPL source-zone remediation for meeting typical environmental cleanup standards and summarize realistic expectations for active source-zone remediation.