Abstract
The presence of multicomponent dense nonaqueous phase liquid (DNAPL) mixtures in porous media can significantly limit the effectiveness of groundwater remediation. A series of column transport and flushing experiments were conducted to quantify the impact of various enhanced flushing agents on dissolution and removal of a multicomponent DNAPL source within a macroscopically homogeneous porous medium. The columns were established with NAPL saturations consisting of an equal mole mixture of cis-1,2-dichloroethene, trichloroethene, and tetrachloroethene. The solubilization agents used included two complexing sugars - hydroxypropyl-β-cyclodextrin (HPCD and methyl-β-cyclodextrin (MCD); a surfactant - sodium dodecyl sulfate (SDS); and a cosolvent - ethanol (EtOH). The chemical flushing agents greatly reduced the time needed to remove each DNAPL component, compared to flushing with water alone. Initial DNAPL-component elution concentrations were successfully predicted using Raoult's Law for MCD, HPCD, and water flushing, indicating that ideal dissolution was initiated by the lower-power enhanced-solubilization agents. EtOH was most efficient at removing the contaminants in terms of normalized mass recovery but least efficient based on a mass-ratio and mole-ratio of contaminant to reagent analysis. SDS was most efficient for contaminant removal when analyzed based on mass-contaminant to mass-reagent recovered and MCD was most effective based on a moles-contaminant to moles-reagent recovered efficiency evaluation. However, in terms of mass flux reduction analysis (i.e. removal metric), SDS was least efficient for contaminant removal compared to all other enhanced-flushing agents tested, especially during the initial stages of DNAPL removal. Results from this study indicate that ideal dissolution was initiated during enhanced-solubilization and that several criteria should be used to evaluate the removal effectiveness of flushing agents for multi-component NAPL systems.
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