Contaminant transport and fate in a source zone of a chlorinated-solvent contaminated superfund site: Overview and initial results of an advanced site characterization project

An advanced site characterization project is being conducted at a chlorinated-solvent contaminated Superfund site to help improve the affectiveness of the remediation program. As a part of this project, two forced-gradient tracer tests were conducted to characterize the transport behavior of bromide and resident trichloroethene and dichloroethene in the aquifer underlying a contaminant source zone. The results indicate significant vertical spatial variability of hydraulic (hydraulic conductivity) and chemical (contaminant concentration) variables over the 6 m thick aquifer zone. The tracer experiments provide a direct demonstration of the influence of subsurface heterogeneity on water flow, and its possible impact on the efficient removal of trichloroethene and dichloroethene by pump and treat. Extensive elution tailing and rebound were observed for trichloroethene and dichloroethene during the experiments, which indicate the presence of a significant mass of contaminant whose transfer to the advecting water is rate limited. This mass could be sorbed to aquifer material, located within low permeability zones, associated with an immiscible-liquid phase, or some combination thereof. Identification of the factors that control contaminant mass removal is critical for a complete, successful cleanup of the site. Current and future research associated with this site targets these issues.