We present the results of a lab-scaled feasibility study to assess the performance of electrical resistivity tomography for detection, characterization, and monitoring of fuel grade ethanol releases to the subsurface. Further, we attempt to determine the concentration distribution of the ethanol from the electrical resistivity tomography data using mixing-models. Ethanol is a renewable fuel source as well as an oxygenate fuel additive currently used to replace the known carcinogen methyl tert-butyl ether; however, ethanol is preferentially biodegraded and a cosolvent. When introduced to areas previously impacted by nonethanol-based fuels, it will facilitate the persistence of carcinogenic fuel compounds like benzene and ethylbenzene, as well as remobilize them to the ground water. These compounds would otherwise be retained in the soil column undergoing active or passive remediation processes such as soil vapor extraction or natural attenuation. Here, we introduce ethanol to a saturated Ottawa sand in a tank instrumented for four-dimensional geoelectrical measurements. Forward model results suggest pure phase ethanol released into a water saturated silica sand should present a detectable target for electrical resistivity tomography relative to a saturated silica sand only. We observe the introduction of ethanol to the closed hydraulic system and subsequent migration over the duration of the experiment. One-dimensional and three–dimensional temporal data are assessed for the detection, characterization, and monitoring of the ethanol release. Results suggest one-dimensional geoelectrical measurements may be useful for monitoring a release, while three-dimensional geoelectrical field imaging would be useful to characterize, monitor, and design effective remediation approaches for an ethanol release, assuming field conditions do not preclude the application of geoelectrical methods. We then attempt to use predictive mixing models to calculate the distribution of ethanol concentration within the measurement domain. For this study we examine four different models: a nested parallel mixing model, a nested cubic mixing model, the complex refractive index model (CRIM), and the Lichtenecker-Rother (L-R) model. The L-R model, modified to include an electrical formation factor geometry term, provided the best agreement with expected EtOH concentrations.

我们展示了实验室规模可行性研究的结果，以评估电阻率断层扫描的性能用于检测、表征和监测向地下释放的燃料级乙醇。此外，我们尝试使用混合模型从电阻率层析成像数据中确定乙醇的浓度分布。乙醇是一种可再生燃料来源，也是一种含氧燃料添加剂，目前用于替代已知的致癌物甲基叔丁基醚；然而，乙醇优先被生物降解并且是助溶剂。当引入以前受非乙醇燃料影响的地区时，它将促进苯和乙苯等致癌燃料化合物的持久存在，并将它们重新移动到地下水中。这些化合物否则会保留在土壤柱中，进行主动或被动修复过程，例如土壤蒸汽提取或自然衰减。在这里，我们将乙醇引入到装有四维地电测量仪器的罐中的饱和渥太华沙子中。正演模型结果表明，相对于仅饱和硅砂，释放到水饱和硅砂中的纯相乙醇应该呈现电阻率层析成像的可检测目标。我们观察到乙醇引入封闭液压系统和随后在实验期间的迁移。评估一维和三维时间数据以检测、表征和监测乙醇释放。结果表明，一维地电测量可用于监测释放，而三维地电场成像可用于表征、监测和设计乙醇释放的有效修复方法，假设现场条件不排除地电的应用方法。然后我们尝试使用预测混合模型来计算测量域内乙醇浓度的分布。在这项研究中，我们研究了四种不同的模型：嵌套平行混合模型、嵌套立方混合模型、复杂模型折射率模型 (CRIM) 和 Lichtenecker-Rother (LR) 模型。LR 模型经过修改以包括电形成因子几何项，提供了与预期 EtOH 浓度的最佳一致性。