Back diffusion of contaminants from secondary sources may hamper site remediation if it is not properly addressed in the remedial design. A review of all reported technologies and strategies that have been or could be applied to address plume persistence due to back diffusion as published in the peer‐reviewed literature is provided. We classify these into four major categories. The first category consists of those approaches that do not include active measures to specifically address contamination in the low permeable zones (LPZs) and can therefore be considered passive LPZ management approaches. A disadvantage of these approaches is the long duration that may be required to meet acceptable endpoints; however, this allows degradation to potentially play a significant part even at modest rates. The remaining three categories all use approaches to specifically address contaminants in the LPZ. The second category consists of strategies that promote contaminant destruction through the forward diffusion of amendments into the LPZ. A variety of laboratory tests indicate concentration or flux reductions range from no improvement, to reductions as high as four orders‐of‐magnitude depending on the evaluation metric. The third category consists of strategies that alter physical characteristics of the secondary source, and includes viscosity modification, fracturing, and soil mixing. Each of these offer unique advantages and are often used to deliver one or more amendments for contaminant treatment. The final category consists of thermal and electrokinetic remediation, both less susceptible to permeability contrast limitations. However, they are not routinely used for secondary‐source treatment.

中文翻译：

---

管理反向扩散风险的策略


如果修复设计中未正确解决，二次污染源污染物的反向扩散可能会阻碍现场修复。提供了对同行评审文献中发表的所有已报告的技术和策略的回顾，这些技术和策略已经或可能用于解决由于反向扩散而导致的羽流持久性问题。我们将它们分为四大类。第一类包括不包括专门解决低渗透区 (LPZ) 污染的主动措施的方法，因此可被视为被动 LPZ 管理方法。这些方法的缺点是可能需要较长的持续时间才能达到可接受的终点；然而，这使得即使在适度的速率下，退化也可能发挥重要作用。其余三类都使用专门解决LPZ污染物的方法。第二类包括通过将修正物向前扩散到LPZ 来促进污染物破坏的策略。各种实验室测试表明，浓度或通量降低范围从没有改善到降低高达四个数量级，具体取决于评估指标。第三类包括改变二次来源物理特性的策略，包括粘度修改、压裂和土壤混合。其中每一种都具有独特的优势，并且通常用于为污染物处理提供一种或多种修正。最后一类包括热修复和电动修复，两者都不易受到渗透性对比限制的影响。然而，它们并不常规用于二级来源治疗。