Polychlorinated biphenyl (PCB) recovery under a building with an in situ technology using micellar solutions

Abstract

This paper presents laboratory studies, numerical modelling, and a soil washing field test as a remedial technology for mass reduction in a source zone of soil contaminated with the polychlorinated biphenyl (PCB) Aroclor 1248 beneath an industrial building. Due to its high viscosity, the Aroclor 1248 is almost immobile in soils at this site. The objective was therefore to select products capable of dissolving the Aroclor in situ. In the laboratory phase, two surfactants and three alcohols were selected using 52 distinct phase diagrams. Alcohols and surfactants used either alone or in combination were tested in sand columns with contaminated soil from the site. The washing solution used in the field test was composed of an anionic surfactant (Nansa HS 85 S, a dodecylbenzene sulfonate) and an alcohol (n-butanol). In laboratory trials, this solution recovered 99% of initial PCBs by dissolution after the injection of 10 pore volumes of solution. During the field test, however, recovery rates reached only 25%. Low recovery can be explained by the presence of a surfactant in the soil prior to the experiment. This surfactant spilled accidentally within the ongoing production activity of the factory was similar to that injected in the experimental cell. It modified the ratio of alcohol to surfactant of the injected washing solution in the soil and caused the formation of a viscous gel, which partially plugged the porous media. Phase diagrams and sand column tests performed with the recovered viscous gel led to the selection of an alcohol (ethanol) that is able to dissolve the gel and recover 99% of the initial PCBs contained in the contaminated soil by dissolution, following the injection of three pore volumes of solution. These laboratory tests showed that in situ flushing technology using micellar and (or) alcohol solutions can potentially be used to reduce the mass of PCB in the source zone, but the application of in situ technologies at industrial facilities is difficult to control because of the risk of presence of other chemicals that might interfere and concrete and other buried structures that might alter the flow behavior.Key words: soil washing, surfactant, alcohol, PCB, in situ technology, porous media clogging.