Effects of initial saturation on properties modification and displacement of tetrachloroethene with aqueous isobutanol

Packed column experiments were conducted to study effects of initial saturation of tetrachloroethene (PCE) in the range of 1.0–14% pore volume (PV) on mobilization and downward migration of the non-aqueous phase liquid (NAPL) product upon contact with aqueous isobutanol (∼ 10 vol.%). This study focused on the consequences of swelling beyond residual saturation. Columns were packed with mixtures of neat PCE, water and glass beads and waterflooded to establish a desired homogeneous residual saturation, and then flooded with aqueous isobutanol under controlled hydraulic conditions. Results showed a critical saturation of approximately 8% PV for these packed column experimental conditions. At low initial PCE saturations (< 8% PV), experimental results showed reduced risk of NAPL-product migration upon contact with aqueous isobutanol. At higher initial PCE saturations (> 8% PV), results showed NAPL-product mobilization and downward migration which was attributed to interfacial tension (IFT) reduction, swelling of the NAPL-product, and reduced density modification. Packed column results were compared with good agreement to theoretical predictions of NAPL-product mobilization using the total trapping number, NT. In addition to the packed column study, preliminary batch experiments were conducted to study the effects of PCE volumetric fraction in the range of 0.5–20% on density, viscosity, and IFT modification as a function of time following contact with aqueous isobutanol (∼ 10 vol.%). Modified NAPL-product fluid properties approached equilibrium within approximately 2 h of contact for density and viscosity. IFT reduction occurred immediately as expected. Measured fluid properties were compared with good agreement to theoretical equilibrium predictions based on UNIQUAC. Overall, this study demonstrates the importance of initial DNAPL saturation, and the associated risk of downward NAPL-product migration, in applying alcohol flooding for remediation of DNAPL contaminated ground water sites.