Facilitated Transport of Organic Contaminants in a High Concentration, Multicomponent Plume

Abstract A field experiment evaluated the transport of organic contaminants in a plume from hazardous waste disposal areas at the Rocky Mountain Arsenal. The plume contained many xenobiotic contaminants, with widely varying expected mobilities. In laboratory tests, the aquifer sediments had shown significant capacity for sorption of organic contaminants from synthetic groundwater, suggesting contaminants’ mobilities in situ could have been retarded. Sediment cores showed sorbed concentrations of contaminants at or below detection levels, suggesting sorption in situ was minimal. The field experiment made direct observations of organic contaminant transport under plume conditions by flushing tracer‐amended organic‐free water through the plume. No contaminants were retarded in their migration compared to the tracer, suggesting negligible sorption of the contaminants in situ. The concentration of colloids, cosolvents (such as alcohols and ketones), and anionic surfactants in the plume were too low to have had a significant effect on contaminant migration. Non‐ionic surfactants, though not monitored, could have reduced sorption somewhat if they had constituted a significant fraction of the uncharacterized dissolved organic carbon. Micro‐ or nano‐plastic particles, though monitored only indirectly, are deemed unlikely to have significantly affected organic solute transport. Microemulsions may have been present and facilitated the transport of contaminants, but only indirect evidence was obtained. Although the specific reasons for the enhanced mobility of organic contaminants could not be confirmed, this research is the first to show that unknown plume components can be responsible for the suppression of sorption, suggesting new lab research is needed to expand understanding of factors affecting sorption.