Cassidy Nigel J
Applied and Environmental Geophysics Group, School of Physical and Geographical Sciences, Keele University, Staffordshire, ST5 5BG UK.
J Contam Hydrol. 2007 Oct 30;94(1-2):49-75. doi: 10.1016/j.jconhyd.2007.05.002. Epub 2007 Jun 2.
Groundwater and sub-surface contamination by Light Non-Aqueous Phase Liquids (LNAPLs) is one of the industrial world's most pressing environmental issues and a thorough understanding of the hydrological, physical and bio-chemical properties of the sub-surface is key to determining the spatial and temporal development of any particular contamination event. Non-invasive geophysical techniques (such as electrical resistivity, electromagnetic conductivity, Ground-Penetrating Radar, etc.) have proved to be successful sub-surface investigation and characterisation tools with Ground-Penetrating Radar (GPR) being particularly popular. Recent studies have shown that the spatial/temporal variation in GPR signal attenuation can provide important information on the electrical properties of the sub-surface materials that, in turn, can be used to assess the physical and hydrological nature of the pore fluids and associated contaminants. Unfortunately, a high percentage of current LNAPL-related GPR studies focus on contaminant mapping only, with little emphasis being placed on characterising the hydrological properties (e.g., determining contaminant saturation index, etc.). By comparing laboratory-based, dielectric measurements of LNAPL contaminated materials with the GPR signal attenuation observed in both contaminated and 'clean' areas of an LNAPL contaminated site, new insights have been gained into the nature of contaminant distribution/saturation and the likely signal attenuation mechanisms. The results show that, despite some practical limitations of the analysis technique, meaningful hydrological interpretations can be obtained on the contaminant properties, saturation index and bio-degradation processes. A generalised attenuation/saturation model has been developed that describes the physical and attenuation enhancement characteristics of the contaminated areas and reveals that the most significant attenuation is related to smeared zone surrounding the seasonally changing water table interface. It is envisaged that the model will provide a basis for the interpretation of GPR data from analogous LNAPL contaminated sites and provide investigators with an appreciation of the merits and limitations of GPR-based, attenuation analysis techniques for hydrological applications.
轻质非水相液体（LNAPLs）对地下水和地下的污染是工业界面临的最紧迫的环境问题之一，而全面了解地下的水文、物理和生物化学特性是确定任何特定污染事件时空发展的关键。非侵入式地球物理技术（如电阻率、电磁导率、探地雷达等）已被证明是成功的地下探测和表征工具，其中探地雷达（GPR）尤为受欢迎。最近的研究表明，GPR信号衰减的时空变化可以提供有关地下材料电学特性的重要信息，进而可用于评估孔隙流体和相关污染物的物理和水文性质。不幸的是，目前与LNAPL相关的GPR研究中，很大一部分仅专注于污染物测绘，很少强调表征水文特性（例如确定污染物饱和度指数等）。通过将基于实验室的LNAPL污染材料的介电测量结果与在LNAPL污染场地的污染区和“清洁”区观测到的GPR信号衰减进行比较，对污染物分布/饱和度的性质以及可能的信号衰减机制有了新的认识。结果表明，尽管分析技术存在一些实际限制，但仍可获得有关污染物性质、饱和度指数和生物降解过程的有意义的水文解释。已开发出一个广义衰减/饱和度模型，该模型描述了污染区域的物理和衰减增强特征，并揭示出最显著的衰减与季节性变化的地下水位界面周围的涂抹带有关。预计该模型将为解释类似LNAPL污染场地的GPR数据提供基础，并使研究人员了解基于GPR的衰减分析技术在水文应用中的优缺点。
