Department of Environmental Sciences and Energy Research, Weizmann Institute of Science, Rehovot 76100, Israel.
J Contam Hydrol. 2012 May 1;132:28-36. doi: 10.1016/j.jconhyd.2012.02.005. Epub 2012 Feb 22.
We present experimental breakthrough curve (BTC) data and a modeling investigation of conservative and sorbing tracer transport in natural soils. By analyzing the data using the continuous time random walk (CTRW) model, we probe the traditional approach of using conservative tracer model parameters as a basis for quantifying the transport of sorbing solutes in the same domain when non-Fickian transport is present. Many known contaminants in groundwater are sorbed to the host solid porous medium, to varying extents, while being transported; this enhances the long tailing of BTCs which often already occurs because of the inherent non-Fickian nature of the transport. The CTRW framework has been shown to account very well for non-Fickian conservative (nonsorbing) transport. Here, we examine two BTC data sets in laboratory columns packed with natural soils; the first (previously analyzed by Mao and Ren (2004)) comprises transport of (conservative) bromide and (sorbing) atrazine tracers, while the second presents new data with bromide and tribromoneopentyl alcohol (TBNPA), a key flame retardant, as a sorbing solute. TBNPA has received little attention in the past, and is shown to be sorbed onto Bet Dagan soil in a nonlinear manner. We find that the transport behavior of bromide is non-Fickian in all cases, which is caused by the heterogeneity of the soil. Comparative model analysis of the non-Fickian BTCs of the conservative, and sorbing tracers and examination of the fitting parameters, exemplify the coupling between transport and adsorption/desorption processes. The difference in transport parameters used to match the conservative and sorbing data sets shows that conservative tracer parameters (average velocity and dispersion coefficient) are not valid for the transport of reactive tracers.
我们展示了保守和吸附示踪剂在天然土壤中传输的实验突破曲线（BTC）数据和建模研究。通过使用连续时间随机游走（CTRW）模型分析数据，我们探究了在存在非菲克运输时，使用保守示踪剂模型参数作为量化同一区域吸附溶质传输的基础的传统方法。许多在地下水中已知的污染物在被运输的同时，不同程度地被吸附到主体固体多孔介质上，这增强了 BTC 常常已经存在的长尾，这通常是由于运输的固有非菲克性质。CTRW 框架已被证明非常适合非菲克保守（非吸附）传输。在这里，我们检查了两个在填充有天然土壤的实验室柱中进行的 BTC 数据集；第一个数据集（以前由 Mao 和 Ren（2004 年）分析）包括（保守）溴化物和（吸附）莠去津示踪剂的传输，而第二个数据集则提供了新的溴化物和三溴新戊醇（TBNPA）的 BTC 数据，TBNPA 是一种关键的阻燃剂，作为吸附溶质。TBNPA 在过去受到的关注较少，并且被显示为以非线性方式被贝塔丹格土壤吸附。我们发现，在所有情况下，溴化物的传输行为都是非菲克的，这是由土壤的非均质性引起的。对保守和吸附示踪剂的非菲克 BTC 的比较模型分析以及拟合参数的检查，例证了传输和吸附/解吸过程之间的耦合。用于匹配保守和吸附数据集的传输参数的差异表明，保守示踪剂参数（平均速度和弥散系数）不适用于反应性示踪剂的传输。
