Thinking Outside the Remediation Toolbox

Thinking Outside the Remediation Toolbox

Treating soil and groundwater contaminants in-situ (or in the ground), without extracting the groundwater or excavating the soil for treatment or offsite disposal, is an approach that offers technical, financial, and scheduling benefits while limiting future liability for many remediation sites. In-situ treatment generally requires delivering a reagent, commonly in a liquid form, into the soil, aquifer, or fractured bedrock. The liquid will disperse into the formation and create conditions whereby contaminants are transformed into non-hazardous compounds by mechanisms such as biological degradation and abiotic chemical reactions. A long-standing challenge for in-situ remediation is how to treat sites with low-permeability soils, such as silt or clay. Efficiently distributing liquids is difficult in these types of sites, which can often result in poor treatment effectiveness. This in turn can lead to substantially increased remediation costs and longer timeframes for our clients. Injection of solid reagents, however, via new, specialized methods can often provide an effective solution for this problem.

It sounds antithetical, but how can solids be distributed effectively into silt and clay, to remediate soil and groundwater? The approach combines injection technologies from the oil and gas industry with soil physics, groundwater hydrology, and chemistry technologies from the environmental industry. A slurry is prepared from a solid treatment reagent such as zero valent iron or potassium permanganate. The slurry entrains the solids into a very viscous and heavy, but flowable, fluid, which can be injected into the ground. In a low-permeability silt and clay formation, injection of this slurry results in a distribution of the reagent in a relatively horizontal, pancake-shaped structure. The solid reagents and other components of the slurry are engineered so that after injection, the emplaced solids and the pancake-shaped structure will have a much higher permeability than the surrounding formation. Because of this contrast in permeability, groundwater is diverted to flow preferentially through the emplaced solids. Contaminants dissolved in the groundwater chemically react with the solids in the structure, transforming them to non-hazardous compounds.

There are many options for designing and applying this approach in a way that tailors the remedy to a site’s specific conditions. For example, the multiple “pancakes” can be stacked at different depths in a formation to construct a vertical treatment barrier. Some types of solids will very slowly dissolve and can chemically diffuse above and below the “pancake,” further expanding the treatment zone vertically. There are also many options for the type of reagent that can be used, which provides a very flexible remedy to address a wide range of contaminants ranging from organic compounds such as solvents to inorganics such as heavy metals.

At Woodard & Curran we strive to develop innovative, effective, and sustainable solutions for our clients. Our core values include designing simpler processes that achieve the same results as more complex, expensive, or energy-intensive processes. This is an example of how thinking outside the toolbox and coupling innovations from different technology sectors can help reinforce that core value and drive more effective solutions to old problems.

Tags: Remediation

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National Practice Leader
In-Situ Remediation

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