In-situ oxidation of trichloroethene by permanganate: effects on porous medium hydraulic properties

• Published in: Journal of contaminant hydrology 2001-07, Vol.50 (1), p.79-98
• Main Authors: Schroth, M.H., Oostrom, M., Wietsma, T.W., Istok, J.D.
• Format: Article
• Language: English
• Subjects: Chemical Precipitation; DNAPL; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Environmental Pollution - prevention & control; Exact sciences and technology; Hydrogeology; Hydrology. Hydrogeology; In-situ oxidation; Oxidation-Reduction; Permanganate; Pollution, environment geology; potassium permanganate; Potassium Permanganate - chemistry; Pressure; Relative permeability; Silicon Dioxide; Solubility; Solvents - chemistry; trichloroethene; Trichloroethylene - chemistry; Water Movements; Water Pollutants, Chemical - analysis
• ISSN: 0169-7722; 1873-6009
• DOI: 10.1016/S0169-7722(01)00098-5

In-situ oxidation of dense nonaqueous-phase liquids (DNAPLs) by strong oxidants such as potassium permanganate (KMnO 4) has been proposed as a possible DNAPL remediation strategy. In this study, we investigated the effects of in-situ trichloroethene (TCE) oxidation by KMnO 4 on porous medium hydraulic properties. In particular, we wanted to determine the overall effects of concurrent solid phase (MnO 2) precipitation, gas (CO 2) evolution and TCE dissolution resulting from the oxidation reaction on the porous medium's aqueous-phase relative permeability, k rw. Three TCE removal experiments were conducted in a 95-cm long, 5.1-cm i.d. glass column, which was homogeneously packed with well-characterized 30/40-mesh silica sand. TCE was emplaced in the sand-pack in residual, entrapped form through a sequence of water/TCE imbibition and drainage steps. The column was then flushed under constant aqueous flux conditions for up to 104 h with either deionized water (reference experiment), deionized water containing 5 mM KMnO 4 or deionized water containing 5 mM KMnO 4 and 300 mM Na 2HPO 4. Aqueous-phase relative permeabilities were computed from measured flow rates and measurements of aqueous-phase pressure head, h obtained using pressure transducers connected to tensiometers distributed along the column length. A dual-energy gamma radiation system was used to monitor changes in fluid saturation that occurred during each experiment. In addition, column effluent samples were collected for chemical analyses. Dissolution of TCE during deionized water flushing led to an increase in k rw by ∼22% and a local reduction in h. On the other hand, vigorous CO 2 gas production and precipitation of MnO 2 was visually observed during flushing with deionized water that contained 5 mM KMnO 4. As a consequence, k rw declined by ∼96% and h increased locally by more than 1000 cm H 2O during the first 24 h of the experiment, causing sand-pack ruptures and pump failure. Conversely, less CO 2 gas production and MnO 2 precipitation was visually observed during flushing with deionized water that contained 5 mM KMnO 4 and 300 mM Na 2HPO 4. Consequently, only small increases in h (