Theme: 01. Remediation Technology Innovations

Topic Area: 01f. Emerging Remediation Technologies

Formatted Title:

Gels as Innovative Fluids for In Situ Remediation: Overview of Projects from Laboratory to Field Scale

Background/Objectives:

In situ remediation usually implies injection in the soil, either to act chemically to degrade contaminants or to act physically to enhance DNAPL mobilization. Typical water-based remediation fluids are subject to gravity and preferential pathways, leading to unpredictable and non-uniform treatment. Polymer gels are also water-based but present a higher viscosity and a shear-thinning behavior that make them less sensitive to soil anisotropy and gravity. This new kind of fluids allow for a more uniform and predictable treatment. Using polymer gels is still a new but very promising approach that could help to improve the efficiency of several remediation techniques (reagent delivery, DNAPL mobilization, confining…).

Approach/Activities:

SERPOL has been part of several R&D projects in which gel formulations were developed at laboratory scale and finally assessed at field scale on several sites. SERPOL also conducted several field pilots on its own using this new type of fluids. It was either to: (a) improve reagent remanence (targeting adsorbed chlorinated compounds) in a high permeability aquifer (GW velocity > 10 m/d), (b) improving lateral delivery of a reagent in the unsaturated zone of a high permeability soil (gravel and pebbles) and (c) recover a DNAPL residual after pure phase pumping using gelled surfactant.

Results/Lessons Learned:

Field applications of the technique were a success. SERPOL prepared and injected about 200 m³ of gel in total on several sites and will share its experience. The most important lessons are that: (a) despite its high viscosity, the shear-thinning behavior of the gel makes it injectable with very little pressure; (b) thanks to its high viscosity, it propagated homogeneously in every direction, including upward and upstream, even when injected in high permeability unsaturated zone; propagation is predictable; (c) radiuses of influence exceeded several meters; (d) in a high velocity aquifer the gel remained in place for more than one year, drastically increasing contact time between soil and reagent; in this case, contaminant degradation was more than 99%; (e) in the gel-occupied soil the water flow is stopped, making it an interesting candidate for temporary confinement; (f) when associated with surfactant, gel nonetheless releases DNAPL trapped droplets from capillary forces but also pushes them thanks to its viscosity leading to very low residual saturation; and (g) gel propagation can easily be monitored using electrical resistance tomography which could be used to drive the treatment.

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Laurent Mansuelle