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首页> 外文学位 >Impacts of Back Diffusion and Biodegradation on MTBE/TBA Plumes and Impacts of Spills of Ethanol-Blended Biofuels on Groundwater: Development of Models for Evaluating Field Experiments and Their Implications.
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Impacts of Back Diffusion and Biodegradation on MTBE/TBA Plumes and Impacts of Spills of Ethanol-Blended Biofuels on Groundwater: Development of Models for Evaluating Field Experiments and Their Implications.

机译：反向扩散和生物降解对MTBE / TBA羽流的影响以及乙醇掺混生物燃料泄漏对地下水的影响：田间试验评估模型的开发及其意义。

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摘要

Fate and transport of bromide tracer, gasoline oxygenates including methyl tert-butyl ether (MTBE), tert-butyl alcohol (TBA), ethanol, and selected petroleum hydrocarbons (benzene, toluene, and o-xylene [BToX]) are studied and simulated using data from field experiments at Site 60, Vandenberg Air Force Base (VAFB), CA.;Conservative tracer experiments can provide information useful for characterizing various subsurface transport properties. High resolution data from a 410-day controlled field experiment at VAFB are used to construct and calibrate a groundwater flow and transport model. The effectiveness of three different types of transport observations (conservative tracer breakthrough curves, first temporal moments of breakthrough curves, and tracer mass discharge through control planes combined with hydraulic head observations) are evaluated for sensitivity analysis and parameter estimation of the site-specific flow and transport model. Results showed the advantages of using temporal moment of conservative tracer and mass discharge as observations for inverse modeling. First temporal moments provided feedback to the model and remained sensitive within a wider range of parameter values than did the other approaches and even when the observed and simulated breakthrough curves did not overlap or the peak concentrations were not similar.;Following a gasoline spill in late 1994 at VAFB, several excavations of the spill area were performed in 1995, 2007, and 2008. However, an MTBE/TBA plume persisted for over 15 years within 200 feet of the original spill source. Available monitoring data and published details about the source are used to develop a two-dimensional reactive transport model of MTBE and its potential metabolite TBA. The analyses suggested that MTBE diffused from the thin anaerobic aquifer into the adjacent anaerobic silts and transformed to TBA in both aquifer and silt layers. At later times TBA was the dominant solute, diffusing back out of the silts into the aquifer, and sustaining plume concentrations much longer than would have been the case in the absence of such diffusive exchange. Aerobic degradation of MTBE or TBA at the water table in the overlying silt layer is shown by the simulations to limit the mass available for back diffusion to the aquifer.;Decreased biodegradation rates of BToX resulting from co-release of ethanol lead to longer plumes than in the absence of ethanol as co-contaminant, and thus potentially greater risks may be posed by gasohol spills. In a previous field study at VAFB, two plumes were created by re-injecting extracted groundwater spiked with BToX in one side, and BT oX plus ethanol in another side for 283 days. A field-calibrated reactive transport model is developed in this study to evaluate the impact of ethanol on fate and transport of BToX species. The model was developed by stepwise inclusion of various reaction processes, as suggested by comparison of model simulations to field data, and drawing on literature for insight into reaction rates and constraints. This iterative process illustrates the limitations of models if not calibrated to or at least founded on field data. Best fits to the experimental data were achieved by incorporating the processes of ethanol fermentation, anaerobic methane oxidation, three dimensional mixing, and microbial growth. The final simulations matched temporal histories for electron donors, acceptors, and products quite well. In particular, the simulations matched the observations that the benzene plume in the With-Ethanol Lane was about 4.5 times longer than in the No-Ethanol Lane due to the slower natural attenuation rate of benzene in the presence of ethanol. This model, which incorporates more reaction processes than models previously applied to investigate ethanol impacts on BTEX fate, can be used to better understand the rate limiting processes, evaluate impacts under different geochemical conditions, and recommend potential remediation techniques.
机译：研究和模拟了溴化物示踪剂，包括甲基叔丁基醚（MTBE），叔丁醇（TBA），乙醇和某些石油烃（苯，甲苯和邻二甲苯[BToX]）的汽油氧化物的去向和运输使用加利福尼亚州范登堡空军基地（VAFB）站点60的现场实验数据；保守的示踪剂实验可以提供有助于表征各种地下运输特性的信息。来自VAFB的410天受控野外实验的高分辨率数据用于构建和校准地下水流量和传输模型。评估了三种不同类型的运输观测的有效性（守恒示踪剂穿透曲线，穿透曲线的第一时间矩以及通过控制面的示踪剂质量排放与水力压头观测值的结合），用于敏感性分析和现场特定流量的参数估计，以及运输模型。结果表明，利用保守示踪剂的瞬时矩和质量流量作为逆模型的观测值具有优势。与其他方法相比，即使在观察到的和模拟的突破曲线不重叠或峰值浓度不相似的情况下，第一时间矩也为模型提供了反馈，并在更宽的参数值范围内保持敏感;;随后发生汽油泄漏1994年，在VAFB，1995、2007和2008年对溢出区域进行了几次开挖。但是，MTBE / TBA羽流在原始溢出源200英尺内持续了15年以上。可用的监测数据和有关源的已发布详细信息用于开发MTBE及其潜在代谢物TBA的二维反应性运输模型。分析表明，MTBE从稀薄的厌氧含水层扩散到相邻的厌氧淤泥中，并在含水层和淤泥层中均转化为TBA。后来，TBA是占主导地位的溶质，从淤泥中扩散回含水层，并且维持羽流浓度比没有这种扩散交换时要长得多。通过模拟显示了上层淤泥层中地下水位MTBE或TBA的有氧降解，从而限制了可用于向后扩散至含水层的质量。乙醇共释放导致BToX的生物降解率降低，导致羽状物比在没有乙醇作为共同污染物的情况下，汽油泄漏可能会带来更大的风险。在VAFB之前的一项野外研究中，通过将一侧注入BToX，另一侧注入BT oX加乙醇的萃取地下水重新注入283天，产生了两个羽状流。在这项研究中开发了现场校准的反应性运输模型，以评估乙醇对BToX物种的命运和运输的影响。该模型是通过逐步包括各种反应过程而开发的，这是通过将模型模拟与现场数据进行比较而得出的，并借鉴了文献以了解反应速率和约束条件。该迭代过程说明了模型的局限性，如果未根据或至少不基于现场数据进行校准。通过结合乙醇发酵，厌氧甲烷氧化，三维混合和微生物生长的过程，获得了与实验数据的最佳拟合。最终的模拟非常适合电子供体，受体和产物的时间历史。尤其是，该模拟与以下观察结果相符：在乙醇存在下，乙醇通道中的苯羽比非乙醇通道中的羽流长约4.5倍，这是因为乙醇存在时苯的自然衰减速率较慢。与先前用于研究乙醇对BTEX命运的影响的模型相比，该模型具有更多的反应过程，可用于更好地了解限速过程，评估不同地球化学条件下的影响并推荐潜在的修复技术。

著录项

  • 作者

    Rasa, Ehsan.;

  • 作者单位

    University of California, Davis.;

  • 授予单位 University of California, Davis.;
  • 学科 Hydrology.;Engineering Environmental.
  • 学位 Ph.D.
  • 年度 2012
  • 页码 131 p.
  • 总页数 131
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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