PARTITIONING OF HYDROPHOBIC ORGANIC-COMPOUNDS TO SORBED SURFACTANTS -2 - MODEL DEVELOPMENT PREDICTIONS FOR SURFACTANT-ENHANCED REMEDIATIONAPPLICATIONS/

A one-dimensional numerical model was developed to simulate the perfor mance of surf acta nt-enhanced remediation (SER) applications for satu rated subsurface systems containing adsorbed hydrophobic organic compo unds (HOCs). The model incorporates temporally and spatially dependent HOC and surfactant mass balance equations to compute distributions in the aqueous, micellar, sorbed surfactant, and subsurface solid phases . In particular, the model accounts for losses of surfactant by sorpti on to the subsurface media and for the subsequent partitioning of HOCs to sorbed surfactant. Parameter values for the model were estimated f rom experimental rate and equilibrium data from the literature, and se nsitivity analysis was conducted to evaluate the model performance and potential SER applications. Simulation results show that the relative affinity of HOCs and surfactants for the immobile subsurface solid ph ase (i.e., the respective retardation factors) is critical for determi ning whether contaminant desorption can be enhanced by surfactants. Fo r example, under the conditions simulated here, removal of phenanthren e and naphthalene from a representative sandy (i.e., low organic carbo n) aquifer is actually hindered by flushing with surfactant solutions, whereas for more hydrophobic contaminants (e.g., pyrene) surfactant a ddition can enhance HOC removal. Likewise, an increase in the organic carbon content of the subsurface solid phase increases the effectivene ss of SER processes. The important rate and equilibrium model paramete rs evaluated in this study provide useful guidelines for the design an d application of SER processes for contaminated subsurface systems and for interpreting SER-related studies.