Experimental Assessment and Modeling of Enhanced Solubilization of Pool-dominated Tetrachloroethene Source Zone in Heterogeneous Porous Media

The purpose of this study is to investigate the elution behavior of pool-dominated dense nonaqueous phase liquid (DNAPL) source zone mass during enhanced solubilization remediation. Flow-cell experiments were first conducted to investigate the performance of different solubilization agents on the DNAPL source zone mass removal in porous media. PCE was used as the model organic liquid, while sodium dodecyl sulfate and Tween 80 surfactants, methyl cyclodextrin (MCD) were selected as enhanced-flushing agents. The porous media considered were silica sand and natural calcareous soil. To gain further insight into the dynamics of source zone depletion, the flushing experiments were modeled using two approaches: a multiphase flow model and a simplified empirically based concentration mass discharge (CMD) model. Results of the flushing experiments indicated that the performance of solubilization agents on PCE source zone depletion was in the following order: Tween 80 > SDS > MCD > > Water. Both models reveal the non-ideal behavior observed during the flooding experiments. For all cases considered, the later stage of mass removal appears to be controlled by the portion poorly accessible mass associated with higher-saturation zones. The advantages and limitations of the two modeling approaches are discussed. It is shown that the two modeling approaches are complementary to each other. Whereas the multiphase model can reveal important aspects of the governing pore-scale processes, the latter approach can provide valuable source term depletion metrics, circumventing the need for detailed definition of DNAPL and porous media parameters.