SURFACTANT ENHANCED REMEDIATION OF SOIL COLUMNS CONTAMINATED BY RESIDUAL TETRACHLOROETHYLENE

The ability of aqueous surfactant solutions to recover tetrachloroethy lene (PCE) entrapped in Ottawa sand was evaluated in four column exper iments. Residual PCE was emplaced by injecting C-14-labeled PCE into w ater-saturated soil columns and displacing the free product with water . Miscible displacement experiments were conducted before and after PC E entrapment to determine the influence of residual PCE on column disp ersivities. The first two column studies involved the injection of a 4 % solution of polyoxyethylene (POE) (20) sorbitan monooleate, resultin g in the removal of 90% and 97% of the residual PCE from 20-30- and 40 -120-mesh Ottawa sand, respectively. Although micellar solubilization of PCE was the primary mode of recovery in these experiments, this pro cess was shown to be rate-limited based on: (a) the disparity between initial steady-state concentrations of PCE in the column effluent and equilibrium values measured in batch experiments; and (b) the increase in effluent concentrations of PCE following periods of flow interrupt ion. In the latter two experiments, surfactant solutions containing mi xtures of sodium sulfosuccinates removed > 99% of the residual PCE fro m soil columns packed with 40-270-mesh Ottawa sand. Approximately 80% of the PCE was mobilized as a separate organic liquid after flushing w ith < 100 mL of these surfactant solutions. This study demonstrates th e capacity of surfactant flushing to enhance the recovery of residual PCE from Ottawa sand and indicates that ultra-low interfacial tensions (< 0.001 dyn cm-1) are not required to achieve significant PCE mobili zation when buoyancy forces are important. The potential for displacem ent of dense nonaqueous-phase liquids as a separate organic phase shou ld, therefore, be evaluated during the selection of surfactant formula tions for aquifer remediation.