Evaluation of Sustained Persulfate Oxidant Release for Remediating Trichloroethylene Contaminated Low Permeability Soil in the Phreatic Zone.

The back diffusion of trichloroethylene (TCE) between low permeability zones (LPZ) and transmissive zones in the subsurface presents remediation challenges. This study investigates in situ chemical oxidation (ISCO) using a sodium persulfate sustained release rod (SPS SR-rod) for potential TCE remediation in the LPZ within a two-dimensional sand tank. The tank simulates a dual permeability porous medium with hydraulic gradients of 0.01 and 0.05. The SPS SR-rod placed within the LPZ released an average PS concentration of ∼625 mg/L laterally, with initial peak concentrations of 7000-10,000 mg/L. When the rod was placed atop the LPZ, lower PS concentrations were observed compared to placement within the LPZ. A separate evaluation of both SPS SR-rod placements in a 2D sand tank injected with pure TCE tested the oxidant's ability to address soil-sorbed TCE. The rod atop the LPZ can mitigate dual permeability layers and creates a depletion zone at the high permeability zone to reduce contaminant transport from the LPZ. The rod within the LPZ reduces TCE lateral dispersion. The persistence and slow release of SPS in the LPZ suggest that the SPS SR-rod could effectively extend the time period of ISCO remediation of low-concentration TCE in the LPZ and the surrounding environment.