Groundwater is an essential natural resource, but vulnerable to contamination, so we spend billions of dollars annually on groundwater remediation. One approach to groundwater remediation is to inject a treatment solution to destroy contaminants in place; this is called in-situ remediation. In-situ remediation often requires spreading an injected plume of treatment solution into the contaminated groundwater, but the laminar flows characteristic of porous media prevent the turbulence that generates plume spreading in most engineered reactors. The resulting difficulty in spreading is a widely recognized, fundamental problem in groundwater remediation.
The research described here, in collaboration with Roseanna Neupauer from the University of Colorado Boulder, approaches this fundamental problem starting with a simple idea from chaos theory: When turbulent mixing is not possible, the best way to spread one fluid into another is by chaotic advection. The essence of chaotic advection is actually quite simple: One needs to impose plume stretching and folding as shown in the animations below. This work, with many other collaborators and students, has established the subfield of engineered injection and extraction.
Along the way, beyond chaotic advection, we have learned how to optimize plume spreading for sorbing solutes, demonstrated reversible hydrodynamic dispersion, and mitigated the notorious wall effect in porous media experiments.
These animations illustrate chaotic advection by engineered injection and extraction (Mays and Neupauer 2012).