Department of Civil Engineering, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
J Contam Hydrol. 2012 Apr 1;131(1-4):79-88. doi: 10.1016/j.jconhyd.2011.12.002. Epub 2012 Jan 3.
Solute transport in clay-rich aquitards is characterized as molecular diffusion- or advection-dominated based on the Péclet number (P(e)). However, few field-based measurements of the coefficient of molecular diffusion (D(e)) exist, and none with a range of advection- or diffusion-dominated conditions in the same aquitard. In this long-term field experiment, standing water in a recovering well was spiked with deuterium ((2)H), then water-level recovery and δ(2)H values were monitored as the well returned to static conditions over 1054 days. After a second (2)H spike, water levels and δ(2)H values were monitored to day 1644 while under near static conditions. Modeling of the second spike was used to define the D(e) of (2)H as (3-4)× 10(-10)m(2)s(-1) for an accessible porosity of 0.31. Reservoir concentrations from the initial spike were modeled to define the transition from advection- to diffusion-dominated transport. This occurred after 200 days, consistent with a transition in P(e) from <1 to >1 when the length term is taken as the radial extent of the tracer plume (normalized concentration <0.05). This study verifies plume extent as the characteristic length term in the calculation of P(e) and demonstrates the transition from advection- to diffusion-dominated transport as the value of P(e) decreases below unity.
在富含粘土的隔水层中，溶质运移的特征是根据佩克莱特数 (P(e)) 表现为分子扩散或对流主导。然而，在同一隔水层中，存在的分子扩散系数 (D(e)) 的现场测量很少，并且没有在对流或扩散主导条件下的范围。在这个长期的现场实验中，在一个恢复井中的静止水中注入氘（(2)H），然后监测水位恢复和 δ(2)H 值，因为井在 1054 天内恢复到静态条件。在第二次 (2)H 注入后，在接近静态条件下监测水位和 δ(2)H 值至第 1644 天。对第二次注入的建模用于将 (2)H 的 D(e) 定义为 (3-4)×10(-10)m(2)s(-1)，可及孔隙度为 0.31。初始注入的储层浓度用于定义从对流到扩散主导传输的转变。这发生在 200 天后，与当长度项取示踪剂羽流的径向扩展（归一化浓度 <0.05）时，P(e) 从 <1 变为 >1 的转变一致。本研究验证了羽流范围作为计算 P(e)中的特征长度项，并证明了当 P(e)值降低到 1 以下时，从对流到扩散主导传输的转变。
