Mobilization of Entrapped Gases in Quasi-Saturated Groundwater Systems Contaminated with Biofuel Additives

Abstract

Biofuel additives have been designed to reduce vehicular emissions to the atmosphere to limit the effects of greenhouse gases on global climate change. The chemical properties of common biofuel additives exhibit ideal characteristics for use in gasoline and diesel, while limiting emissions from exhaust. As biofuel additives begin to be administered regularly to gasoline and fuel sources, the compounds will appear in spill sites, posing a risk to groundwater sources. The interactions that occur between common biofuel additives and trapped gases below the water table were analyzed in this work to further understand the potential consequences on quasi-saturated groundwater zones. The behaviour of trapped gases contaminated with different biofuel additives were analyzed in laboratory experiments conducted in a two-dimensional flow cell to demonstrate the mechanisms of gas flow through a capillary barrier resulting from modified interfacial properties in the presence of a chemical surfactant. Contamination of gas-fluid interfaces by applied biofuel additives at the pore scale resulted in the breakthrough of gas through the capillary barrier. Gas migration terminated at a critical pool height proportional to the reduction in interfacial tension induced by the administered biofuel additives. To further demonstrate the relationship between interfacial tension and critical gas pool height, an interfacial tension-macroscopic invasion percolation model was developed to simulate the transport mechanisms and behaviours of gas flow when an immobile pool is contaminated with 1-Butanol. The findings in this study provide a fundamental understanding of the mechanisms and behaviours of gas mobilization in the presence of common biofuel additives.