Enhanced-Solubilization of a Multi-Component Immiscible Liquid Source Zone Within an Intermediate-Scale Flow Cell System

Developing accurate risk assessments and remediation strategies for sites contaminated by multi-component immiscible liquid depends upon appropriate characterization of the immiscible-liquid (NAPL) mixture, source zone distribution/architecture, subsurface heterogeneity/structure, and the cleanup criteria established for a particular site.  A series of two dimensional flow cell experiments was conducted to quantify the effectiveness of two different flushing agents on the removal of a uniformly distributed multi-component NAPL source zone. The source zone was established with a 10% NAPL saturation consisting of equal mole fractions of tetrachloroethene (PCE), trichloroethene (TCE), and cis-1,2-dichloroethene (DCE). The solubilization agents investigated included 5-wt% solution of a complexing sugar, hydroxypropyl-β-cyclodextrin (HPCD), and a 5-wt% solution of a surfactant, sodium dodecyl sulfate (SDS). The results of these experiments indicate that SDS was more efficient at mass removal compared to HPCD for the integrated extraction port. Similar removal behavior was observed for both flushing agents in which the low solubility component (PCE) of the NAPL mixture showed least efficient removal in terms of moles-contaminant/moles-reagent removed; and the high solubility component (DCE) showed least efficient removal based on mass-contaminant/mass-reagent removed. Although the source zone port (down-gradient edge of source zone) showed similar removal efficiency trends for the low and high solubility components, HPCD showed slightly greater mass removal efficiency for the higher solubility components (DCE and TCE) compared to SDS. For the integrated extraction port, SDS showed slightly more ideal removal in terms of mass flux behavior. These findings suggest that removal efficiencies depend upon the flushing agent itself, the solubility and properties of the individual components of the NAPL mixture, and the proximity of the extraction well/port to the NAPL source. The selection of a particular flushing agent should be evaluated carefully prior to remediation as the mass flux and removal behavior of each component can vary significantly.