Experiments and Simulations on Plume Spreading by Engineered Injection and Extraction in Refractive Index Matched Porous Media

Engineered injection and extraction (EIE) is an in situ groundwater remediation strategy that imposes an engineered spatially and temporally varying velocity field to spread an amendment into the contaminant plume to promote mixing and contaminant degradation through reaction. Here we present a coordinated suite of laboratory experiments and numerical simulations that apply EIE using two pumping sequences: A folding sequence that manipulates plume geometry by stretching and folding, and an oscillating sequence that imposes velocity perpendicular to the plume interface in accordance with previously‐reported active spreading theory. Laboratory experiments investigated spreading and mixing of a non‐reactive tracer using refractive index matched porous media and laser‐induced fluorescence, with remarkable reproducibility between replicates. Numerical simulations matched the experimental results and simulated reactive transport by post‐processing sequentially injected non‐reactive tracer plumes representing the contaminant and the amendment assuming rapid reaction (i.e., high Damköhler number). This study provides the first experimental verification of EIE using Darcy‐scale imaging, demonstrates a novel experimental method to mimic reactive transport at the high‐Damköhler number limit, and confirms active spreading theory. Key Points Engineered injection and extraction has been demonstrated experimentally and numerical simulations have high spatial correlation A novel experimental method is presented to simulate reactive transport at the high‐Damköhler number limit Results confirm active spreading theory: Reaction increases when the groundwater velocity is perpendicular to the plume interface