Numerical simulation of DNAPL source zone remediation with in situ chemical oxidation (ISCO)

Numerical simulations were conducted to evaluate the efficacy of in situ field scale chemical oxidation (ISCO) (with permanganate) for trichloroethylene (TCE) and tetrachloroethylene (PCE) DNAPL in eight idealized heterogeneous porous media sites. The goal of this work was to study the effects of DNAPL source zone remediation at the site scale utilizing a high-resolution three-dimensional numerical model. The model results demonstrated that both dissolution (no treatment) and treatment were unable to completely deplete DNAPL mass or boundary mass flux for any of the sites over a 10 year period. Performance was highly variable due to competition with oxidizable organic aquifer materials, manganese dioxide (rind) formation, DNAPL architecture, and geologic characteristics. When compared to dissolution only, DNAPL mass depletion at the end of treatment ranged from adverse impacts to a three-fold improvement, but diminished with post-treatment monitoring. Similarly, the relative reduction in boundary mass flux varied between unity and a factor of two at the termination of treatment, but at 10 years ranged from a 10-fold reduction to adverse impacts. During the post-treatment phase of the simulations, most of the benefits achieved during active treatment were negated due to dissolution tailing.

► Partial removal of DNAPL source zones yields limited long-term benefits.
► DNAPL mass removal is largely controlled by the geostatistics of the domain.
► Permanganate will be competitively consumed by natural oxidant demand.
► Rind formation adversely impacts treatment efficacy.
► Mass flux rebounds due to dissolution from recalcitrant DNAPL and back diffusion.