Permanganate flushing of DNAPL source zones: Experimental and numerical investigation

In situ chemical oxidation (ISCO) is a potentially effective technology for remediating aquifers contaminated with dense, non-aqueous phase liquids (DNAPLs) such as trichloroethene (TCE) and perchloroethene (PCE). These contaminants dissolve slowly in groundwater; however, the dissolution rate is enhanced by the addition of a concentrated oxidant. As part of this research, an ISCO field experiment was completed at an experimental site at Canadian Forces Base Borden. A small DNAPL source zone containing both residual PCE and TCE was flushed with a 8 g/L permanganate solution for 485 days.; Recycling of the residual permanganate in the extraction wells was used to minimize the mass of the oxidant injected into the treatment zone and the volume of effluent permanganate solution requiring treatment. In total, 892 kg of permanganate were injected into the treatment zone while 303 kg were recaptured by the recycling system.; Groundwater monitoring during the oxidant flush focussed on characterizing the spatial distributions of permanganate and chloride in groundwater. While the injection system successfully flushed the source zone with the concentrated pemanganate solution, the monitoring data suggested that some of the oxidant migrated below the capture zone of the extraction wells. Measurements of the chloride concentration down-gradient of the source zone were used to indicate the removal of DNAPL mass. Interpretation of the chloride concentrations measured in the extraction wells was complicated by the recycling of chloride along with the residual oxidant and provided little information on the rate of DNAPL mass removal.; The performance of the oxidant flush was assessed by comparing the extent of groundwater contamination before and after the oxidant flush. Specific performance measures included the reductions in DNAPL mass, peak solvent concentration, and solvent plume load. While the groundwater data indicated that some DNAPL was present in the source, DNAPL was not detected in soil samples collected from the source, emphasising the difficulty of evaluating DNAPL mass in the field. Plume loading was identified as the most useful performance measurement. The oxidant flush reduced the loads of TCE and PCE in the groundwater plume by 99% and 90%, respectively. (Abstract shortened by UMI.)...