Department of Earth and Environmental Sciences, University of Waterloo, 200 University Ave. W., Waterloo, Ontario, Canada.
J Contam Hydrol. 2011 Jan 25;119(1-4):25-43. doi: 10.1016/j.jconhyd.2010.08.007. Epub 2010 Sep 25.
Ethanol use as a gasoline additive is increasing, as are the chances of groundwater contamination caused by gasoline releases involving ethanol. To evaluate the impact of ethanol on dissolved hydrocarbon plumes, a field test was performed in which three gasoline residual sources with different ethanol fractions (E0: no ethanol, E10: 10% ethanol and E95: 95% ethanol) were emplaced below the water table. Using the numerical model BIONAPL/3D, the mass discharge rates of benzene, toluene, ethylbenzene, xylenes, trimethylbenzenes and naphthalene were simulated and results compared to those obtained from sampling transects of multilevel samplers. It was shown that ethanol dissolved rapidly and migrated downgradient as a short slug. Mass discharge of the hydrocarbons from the E0 and E10 sources suggested similar first-order hydrocarbon decay rates, indicating that ethanol from E10 had no impact on hydrocarbon degradation. In contrast, the estimated hydrocarbon decay rates were significantly lower when the source was E95. For the E0 and E10 cases, the aquifer did not have enough oxygen to support complete mineralization of the hydrocarbon compounds to the extent suggested by the field-based mass discharge. Introducing a heterogeneous distribution of hydraulic conductivity did little to overcome this discrepancy. A better match between the numerical model and the field data was obtained assuming partial degradation of the hydrocarbons to intermediate compounds. Besides depending on the ethanol concentration, the impact of ethanol on hydrocarbon degradation appears to be highly dependent on the availability of electron acceptors.
乙醇作为汽油添加剂的使用量正在增加，由此导致的含乙醇汽油释放物污染地下水的几率也在增加。为了评估乙醇对溶解烃羽流的影响，进行了一项野外试验，在该试验中，将三种具有不同乙醇分数的汽油残留源（E0：无乙醇、E10：10%乙醇和 E95：95%乙醇）置于地下水位以下。使用数值模型 BIONAPL/3D，模拟了苯、甲苯、乙苯、二甲苯、三甲苯和萘的质量排放速率，并将结果与多水平采样器的采样横截面对比。结果表明，乙醇迅速溶解并作为短段向下游迁移。E0 和 E10 源的烃类物质的质量排放量表明，其一级烃类衰减速率相似，这表明来自 E10 的乙醇对烃类降解没有影响。相比之下，当源为 E95 时，估计的烃类衰减速率明显较低。对于 E0 和 E10 情况，含水层中没有足够的氧气来支持烃类化合物完全矿化为现场质量排放量所表明的程度。引入水力传导率的非均匀分布对克服这种差异几乎没有作用。假设烃类部分降解为中间化合物，可使数值模型与野外数据之间的匹配更好。除了依赖于乙醇浓度之外，乙醇对烃类降解的影响似乎还高度依赖于电子受体的可用性。
