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Back Diffusion from Thin Low Permeability Zones

机译：从薄的低渗透区向后扩散

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摘要

Aquitards can serve as long-term contaminant sources to aquifers when contaminant mass diffuses from the aquitard following aquifer source mass depletion. This study describes analytical and experimental approaches to understand reactive and nonreactive solute transport in a thin aquitard bounded by an adjacent aquifer. A series of well-controlled laboratory experiments were conducted in a two-dimensional flow chamber to quantify solute diffusion from a high-permeability sand into and subsequently out of kaolinite clay layers of vertical thickness 15 mm, 20 mm, and 60 mm. One-dimensional analytical solutions were developed for diffusion in a finite aquitard with mass exchange with an adjacent aquifer using the method of images. The analytical solutions showed very good agreement with measured breakthrough curves and aquitard concentration distributions measured in situ by light reflection visualization. Solutes with low retardation accumulated more stored mass with greater penetration distance in the aquitard compared to high-retardation solutes. However, because the duration of aquitard mass release was much longer, high-retardation solutes have a greater long-term back diffusion risk. The error associated with applying a semi-infinite domain analytical solution to a finite diffusion domain increases as a function of the system relative diffusion length scale, suggesting that the solutions using image sources should be applied in cases with rapid solute diffusion and/ or thin clay layers. The solutions presented here can be extended to multilayer aquifer/low-permeability systems to assess the significance of back diffusion from thin layers.
机译：在含水层源质量耗尽后，当污染物质量从含水层扩散时，无水层可以作为含水层的长期污染物源。这项研究描述了分析和实验方法，以了解由相邻含水层界定的稀薄阿奎德中的反应性和非反应性溶质传输。在二维流动室中进行了一系列良好控制的实验室实验，以定量分析溶质从高渗透性砂进入垂直厚度为15 mm，20 mm和60 mm的高岭石粘土层以及随后从中流出的情况。使用图像方法，开发了一维解析解决方案，用于在有限的基层中进行扩散，并与相邻的含水层进行质量交换。分析解决方案与通过光反射可视化现场测得的穿透曲线和阿奎塔德浓度分布显示出非常好的一致性。与高延迟溶质相比，具有低延迟的溶质在水准仪中积累更多的存储质量，并具有更大的穿透距离。但是，由于透明物质大量释放的持续时间更长，因此高延迟溶质具有更大的长期向后扩散风险。将半无限域分析解决方案应用于有限扩散域的误差随着系统相对扩散长度尺度的增加而增加，这表明使用图像源的解决方案应在溶质快速扩散和/或粘土稀薄的情况下应用层。此处介绍的解决方案可以扩展到多层含水层/低渗透性系统，以评估从薄层向后扩散的重要性。

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  • 来源
    《Environmental Science & Technology》 |2015年第1期|415-422|共8页
  • 作者

    Minjune Yang; Michael D. Annable; James W. Jawitz;

  • 作者单位

    Soil and Water Sdence Department, University of Florida, Gainesville, Florida 32611, United States;

    Department of Environmental Engineering Sciences, University of Florida, Gainesville, Florida 32611, United States;

    Soil and Water Sdence Department, University of Florida, Gainesville, Florida 32611, United States;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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  • 正文语种 eng
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