Yu Soonyoung, Freitas Juliana G, Unger Andre J A, Barker James F, Chatzis John
Department of Earth and Environmental Sciences, University of Waterloo, 200 University Ave. W., Waterloo, Ontario, Canada N2L 3G1.
J Contam Hydrol. 2009 Feb 27;105(1-2):1-17. doi: 10.1016/j.jconhyd.2008.11.006. Epub 2008 Nov 17.
Blending of ethanol into gasoline as a fuel oxygenate has created the scenario where inadvertent releases of E95 into soil previously contaminated by gasoline may remobilize these pre-existing NAPLs and lead to higher dissolved hydrocarbon (BTEX) concentrations in groundwater. We contribute to the development of a risk-based corrective action framework addressing this issue by conducting two laboratory experiments involving the release of ethanol into a gasoline source zone established in the capillary fringe. We then develop and apply the numerical model CompFlow Bio to replicate three specific experimental observations: (1) depression of the capillary fringe by the addition of the gasoline fuel mixture due to a reduction in the surface tension between the gas and liquid phases, (2) further depression of the capillary fringe by the addition of ethanol, and (3) remobilization of the gasoline fuel mixture LNAPL source zone due to the cosolvent behaviour of ethanol in the presence of an aqueous phase, as well as a reduction in the interfacial tension between the aqueous/non-aqueous phases due to ethanol. While the simulated collapse of the capillary fringe was not as extensive as that which was observed, the simulated and observed remobilized non-aqueous phase distributions were in agreement following ethanol injection. Specifically, injection of ethanol caused the non-aqueous phase to advect downwards toward the water table as the capillary fringe continued to collapse, finally collecting on top of the water table in a significantly reduced area exhibiting higher saturations than observed prior to ethanol injection. Surprisingly, the simulated ethanol and gasoline aqueous phase plumes were uniform despite the redistribution of the source zone. Dissolution of gasoline into the aqueous phase was dramatically increased due to the cosolvency effect of ethanol on the non-aqueous phase source zone. We advocate further experimental studies focusing on eliminating data gaps identified here, as well as field-scale experiments to address issues associated with ethanol-BTEX biodegradation and sorption within the development of a risk-based corrective action framework.
将乙醇作为燃料含氧化合物混入汽油中，导致了这样一种情况：E95意外泄漏到先前被汽油污染的土壤中，可能会使这些先前存在的非水相液体重新流动，从而导致地下水中溶解烃（BTEX）浓度升高。我们通过进行两项实验室实验来推动基于风险的纠正行动框架的发展，这两项实验涉及将乙醇释放到毛细管带中建立的汽油源区。然后，我们开发并应用数值模型CompFlow Bio来复制三个特定的实验观察结果：（1）由于气液相之间表面张力的降低，添加汽油燃料混合物导致毛细管带下降；（2）添加乙醇导致毛细管带进一步下降；（3）由于乙醇在水相存在下的助溶行为，以及乙醇导致水相/非水相之间界面张力的降低，汽油燃料混合物轻非水相液体源区重新流动。虽然模拟的毛细管带坍塌不如观察到的那么广泛，但在注入乙醇后，模拟和观察到的重新流动的非水相分布是一致的。具体而言，注入乙醇导致非水相随着毛细管带继续坍塌而向下平流至地下水位，最终在地下水位上方的一个显著缩小的区域聚集，该区域的饱和度高于注入乙醇之前观察到的饱和度。令人惊讶的是，尽管源区重新分布，但模拟的乙醇和汽油水相羽流是均匀的。由于乙醇对非水相源区的助溶作用，汽油在水相中的溶解显著增加。我们主张进一步开展实验研究，重点是消除此处发现的数据差距，以及开展现场规模的实验，以解决基于风险的纠正行动框架发展过程中与乙醇 - BTEX生物降解和吸附相关的问题。
