UBC Theses and Dissertations
Experimental investigation on the fate of ethanol-blended fuels in the subsurface Devries, Jarod Michael
Currently, the North American market for motor fuels is distributing E10 (gasoline with an ethanol content up to 10%). Recent legislature is promoting a range of higher ethanol content fuels to be introduced into the market. The result is an increased risk of accidental release of these higher ethanol content fuels. A comprehensive understanding of the fate of ethanol-blended fuels, including interactions between its constituents (e.g. ethanol, benzene and toluene), degradation products (e.g. VFAs, CO₂, CH₄) and potential secondary water quality impacts (e.g. Mn²⁺,Fe²⁺), is lacking. Eight large columns were constructed to evaluate the impacts of fuel blends of varying ethanol contents on biodegradation, and to determine the effect of soil type on gas generation and migration. In each scenario, approximately 2L of fuel was injected into the lower quarter of the column, approximately 30cm above the water table. The saturated zone was analyzed for dissolved Mn and Fe, as well as EtOH and VFAs. Vadose zone analysis focused on measuring surficial CO₂ and CH₄ fluxes, in-situ soil gas concentrations of CO₂, CH₄, O₂, N₂, and Ar, as well as benzene and toluene. Isotopic analysis of vadose zone CO₂ was also completed. The results confirm that ¹³C isotopic analysis is well suited for identifying the predominant microbial substrate undergoing biodegradation. Fuel blends with higher ethanol content showed more elevated levels of dissolved Mn and Fe, demonstrating that metal mobilization occurs more readily in spills with higher ethanol content. Additionally, fuels with a higher ethanol content exhibited signs of elevated microbial stress through the increased production of butyric acids. Benzene and toluene measured near surface, and the surficial effluxes of CO₂ or CH₄ did not indicate a significant SVI risk in any of the scenarios tested, under the conditions studied.
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