Contribution 5
Submitted by: Kristin Sample-Lord, Villanova University, USA
Slide demonstrating the relative contributions of advection and diffusion to total contaminant flux through a low permeability barrier
Sample Description
(1) Course Name/Type: Geoenvironmental Engineering / Elective course for seniors (4th year) in a civil and/or environmental engineering undergraduate program, and/or graduate students in a 1st year master’s or PhD degree program.
(2) Course Emphasis: contaminant transport, waste and chemical containment, engineered barriers
(3) Descriptive Title of Sample: slide demonstrating the relative contributions of advection and diffusion to total contaminant flux through a low permeability barrier
(4) Brief Teaching Note: The slide conveys the importance of diffusion when evaluating contaminant transport through low permeability materials and assessing long-term performance of engineered barriers, e.g., compacted clay liners, geosynthetic clay liners, cutoff walls. The animations correspond to the following major points: (1) The purpose of the engineered barrier is to act as a low-permeability layer that restricts contaminants from entering the environment. (2) The most important property is that it has low hydraulic conductivity, k, such that flux of liquid and contaminants due to a hydraulic gradient (advection) is minimized. (3) Since k is very low, you often have more contaminant transport occurring due to diffusion than advection. Diffusion is driven by a gradient in chemical potential across the barrier. (4) The example plot on the right side demonstrates the importance of diffusion (see webinar or original reference). Neglecting diffusion results in unconservative estimates of breakthrough times.
(5) References: This slide was presented as part of the webinar, “Advances in Diffusion and Membrane Behavior of Bentonite-Based Barriers”, by Dr. Kristin Sample-Lord on 7 May 2021, as part of the International Geoenv. Engineering Webinar Series. See 10:00-16:30 at the following link: https://www.youtube.com/watch?
Plot modified from: Shackelford (2013). The ISSMGE Kerry Rowe Lecture: The role of diffusion in environmental geotchnics. Canadian Geotechnical Journal, 51, 1219-1242.
This work is licensed under a Creative Commons Attribution 4.0 International License.