Civil and Environmental Engineering Department, 1500 Illinois St, Golden, CO 80401, USA.
Ground Water. 2013 Mar;51(2):229-36. doi: 10.1111/j.1745-6584.2012.00962.x. Epub 2012 Jul 26.
The release of stored dissolved contaminants from low permeability zones contributes to plume persistence beyond the time when dense nonaqueous phase liquid (DNAPL) has completely dissolved. This is fundamental to successfully meeting acceptable low concentrations in groundwater that are driven by site-specific cleanup goals. The study goals were to assess the role of DNAPL entrapment morphology on mass storage and plume longevity. As controlled field studies are not feasible, two-dimensional (2D) test tanks were used to quantify the significance of mass loading processes from source dissolution and stored mass rebound. A simple two-layer soil domain representing a high permeable formation sand overlying a zone of lower permeability sand was used in the tests. DNAPL mass depletion through dissolution was monitored via X-ray photon attenuation, and effluent samples were used to monitor the plume. These data enabled analysis of the DNAPL distribution, the dissolved plume, and the dissolved phase distribution within the low permeability layer. Tests in an intermediate tank showed that mass storage contributes substantially to plume longevity. Detectable effluent concentrations persisted long after DNAPL depletion. The small tank results indicated that the DNAPL morphology influenced the flow field and caused distinctive transport mechanisms contributing to mass storage. Zones of high DNAPL saturation at the interface between the low and high permeability layers exhibited flow bypassing and diffusion dominated transport into the low permeability layer. In the absence of a highly saturated DNAPL zone near the soil interface the contaminant penetrated deeper into the low permeability layer caused by a combination of advection and diffusion.
从低渗透性区域释放储存的溶解污染物会导致污染羽带的持续存在，超过致密非水相液体 (DNAPL) 完全溶解的时间。这对于成功实现基于特定地点的清理目标的地下水可接受的低浓度是至关重要的。本研究的目的是评估 DNAPL 捕获形态对质量储存和污染羽带持久性的作用。由于无法进行受控的现场研究，因此使用二维（2D）测试槽来量化源溶解和储存质量反弹过程的质量加载过程的重要性。在测试中，使用了一个简单的两层土壤域，代表高渗透性地层砂上覆有低渗透性砂区。通过 X 射线光子衰减监测 DNAPL 通过溶解的质量消耗，并用流出物样品监测污染羽带。这些数据使我们能够分析 DNAPL 分布、溶解羽带和低渗透性层内的溶解相分布。在中间槽中的测试表明，质量储存对污染羽带的持久性有很大贡献。在 DNAPL 耗尽后很长时间仍能检测到流出物浓度。小槽的结果表明，DNAPL 形态会影响流场，并导致独特的传输机制，从而促进质量储存。在低渗透性层和高渗透性层之间的界面处，高 DNAPL 饱和度区域表现出绕过流动和扩散为主的传输进入低渗透性层的现象。在没有靠近土壤界面的高饱和 DNAPL 区的情况下，由于对流和扩散的组合作用，污染物会更深地渗透到低渗透性层中。
