Surfactant-enhanced aquifer remediation:
Flow container experiments
The remediation of aquifers by conventional pump-and-treat technologies
is often an inefficient and costly undertaking, particularly when nonaqueous
phase liquids (NAPLs) are present. The failure of this technique
can be attributed, in large part, to the low aqueous solubilities of most
NAPLs and their relatively slow rates of mass transfer into the aqueous
phase. To overcome such limitations, surfactants have been proposed
as a means of enhancing the performance of pump-and-treat systems based
on their ability to increase the aqueous solubility of hydrophobic organic
compounds via micellar solubilization and to mobilize entrapped NAPLs due
to interfacial tension reductions. Although laboratory studies have
demonstrated the capacity of surfactants to recover NAPLs from porous media,
field studies conducted to date have achieved mixed results. In order
to facilitate more effective transfer of this technology from the laboratory
to the field, we participated in the investigation of the influence of
scale and formation heterogeneity on the entrapment and surfactant-enhanced
recovery of denser-than-water NAPLs (DNAPLs) in two-phase aquifer systems.
To accomplish this objective we took part in the following tasks: (I) assessment
of DNAPL infiltration and entrapment in 2-dimensional aquifer systems of
varying scale and heterogeneity; and (II) evaluation of SEAR (Surfactant
Enhanced Aquifer Remediation) for DNAPL recovery in heterogeneous 2-dimensional
aquifer systems. The 2-D experiments were conducted in rectangular
aquifer models equipped with a dual-energy gamma radiation system capable
of measuring soil bulk density and porosity, as well as DNAPL saturations.
The figure presented below shows the evolution of a tetrachloroethylene
(PCE) spill during surfactant flushing, as recorded by gamma radiation
scanning.
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