[1] Traditional continuum-based multiphase simulators incorporate a capillary pressuresaturation relationship that assumes instantaneous attainment of equilibrium following a disturbance. This assumption may not be appropriate for systems where the capillary pressure is a function of the rate of change of saturation, a phenomenon referred to as dynamic capillary pressure. Previous studies have investigated the impact of soil and fluid properties on dynamic effects in capillary pressure; however, the impact of wettability on this phenomenon has not been investigated to date. In this study, two-phase multistep outflow (MSO) experiments conducted in chemically treated sands with different equilibrium contact angles were used to investigate the influence of wettability variations on dynamic effects in capillary pressure during displacement of water by tetrachloroethene (PCE). Data from the MSO experiments were modeled with a multiphase flow simulator that includes dynamic effects and were also analyzed through comparisons with theoretical model predictions for interface movement in a single capillary tube. Results showed that a faster approach to equilibrium, characterized by smaller fitted damping coefficients, occurred in sands with larger equilibrium contact angles. Damping coefficients for sands with an operational contact angle greater than 80°were found to be an order of magnitude smaller than those with an operational contact angle less than 65°. These results suggest that it may be possible to neglect dynamic effects in capillary pressure in systems that approach intermediate-wet conditions but that these effects will be increasingly important in more water-wet systems.
A vital design parameter for any in situ chemical oxidation system using permanganate (MnO4-) is the natural oxidant demand (NOD), a concept that represents the consumption of MnO4- by the naturally present reduced species in the aquifer solids. The data suggest that the NOD of the aquifer material from Canadian Forces Base Borden used in our study is controlled by a fast or instantaneous reaction captured by the column experiments, and a slower reaction as demonstrated by both column and batch test data. These two reaction rates may be the result of the reaction of MnO4- with at least two different reduced species exhibiting widely different rates of permanganate consumption (fast rate >7 g of MnO4- as KMnO4/kg/day and slow rate of approximately 0.005 g/kg/day), or a physically/chemically rate-limited single species. The slow NOD reaction prevented fulfillment of the ultimate NOD during the days- to months-long batch experiments and allowed significant early MnO4- breakthrough (>98%) during transport in the column experiments. A large fraction of the organic carbon resisted oxidation over the 21-week duration of the batch experiments. This result demonstrates that NOD estimated from total organic carbon measurements can significantly overpredict the NOD value required in the design of an in situ chemical oxidation application.
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