Focused flow during water infiltration into ethanol-contaminated unsaturated porous media

Abstract

The increasing commercial and industrial use of ethanol, i.e., in biofuel and gasoline, has generated increased incidents of vadose zone contamination by way of ethanol spills and releases. This has increased the interest in better understanding infiltration behaviours of ethanol in unsaturated porous media and the multiphase interactions in the vadose zone. Solute-dependent capillarity-induced focused flow (SCIFF) is a vertical, highly focused flow infiltration behaviour first reported by Smith et al. (2011) in butanol-contaminated sands. Through the use of highly controlled laboratory experiments, this thesis research investigates focused flow (SCIFF) and related behaviours through water infiltration into ethanol-contaminated unsaturated sand.

Focused flow behaviours (SCIFF) were demonstrated through the infiltration of water into an ethanol-contaminated unsaturated sand using both constant flux and constant head methodologies. The observation of focused flow behaviours in ethanol-contaminated sand supported the primary hypothesis of this work. The secondary hypothesis was also supported, as focused flow behaviours were not observed, rather stable semicircular infiltration patterns were observed during ethanol infiltration into water-wet sand. Comparisons between constant flux and constant head application methods under similar flow rates and fluid volumes produced similar results. The zone of lower saturation, or the “halo effect” reported in previous literature, was strongly expressed during water infiltration in ethanol-contaminated sand. This halo effect is affected by the maximum (at 40% to 50%) of aqueous concentration of ethanol. This maximum enhances the zone of lower saturation and stabilizes the solute front. The SCIFF focused flow also overcame the effects of minor heterogeneities in the sand. However, additional laboratory and modelling work is required to further understand the extent of SCIFF behaviour.