NEWS 2019

Posted April 30, 2019 (updated May 15, 2019)

Event: June 5, 2019

GSE/CGS CCLT: Dr. Charles Shackelford, Colorado State University - The Role of Diffusion in Environmental Geotechnics

Location: German Canadian Cultural Association (8310 Roper Road)

Time: 11:30am Registration, 12:00pm Lunch, 12:20pm Presentation

Cost: $25 Members, $30 Non-Members, $15 Students

Diffusion of contaminants can play a significant if not dominant role in many applications encountered within the field of environmental geotechnics. The objective of this presentation is to provide an overview of the important role diffusion plays in such applications. The presentation proceeds from a historical perspective, beginning with the recognition in the late 1970s to early 1980s that diffusion may be an important process in assessing contaminant migration through low permeability barriers in waste containment applications. Data from the literature and simplified model simulations are used to illustrate under what conditions diffusion is important, and the significance of diffusion with respect to different barrier components and types of barriers in waste containment applications is illustrated. The barriers considered include natural clays, compacted clay liners, geomembrane liners, geosynthetic clay liners, composite liners, vertical cutoff walls, subaqueous caps for contaminated sediments, and highly compacted bentonite buffers for high level radioactive waste containment. The significance of semipermeable membrane behavior on liquid-phase diffusion through bentonite-based barriers also is highlighted. The potential importance of matrix diffusion as an attenuation mechanism for contaminant transport is illustrated, and the roles of both liquid-phase and gas-phase diffusion under unsaturated conditions are discussed. Finally, the role of diffusion in terms of remediation applications is illustrated via an example analysis illustrating the impact of reverse matrix or back diffusion on the effectiveness of pump-and-treat remediation, as well as via a summary of several diffusion based models commonly used to describe the leaching of contaminants from stabilized and solidified from a variety of waste forms.

Charles D. Shackelford, Ph.D., P.E., F.ASCE is Professor and Head of the Department of Civil and Environmental Engineering, Colorado State University, Fort Collins, Colorado, USA. He has 35 years of experience pertaining to the geoenvironmental engineering aspects of waste management and environmental remediation, is a licensed professional (civil) engineer (P.E.) in California and Colorado, and has served as an expert on waste disposal issues on numerous occasions for private companies and federal and international agencies (e.g., International Atomic Energy Agency). Dr. Shackelford's research is focused primarily on evaluating flow (seepage) and transport of liquids and contaminants through engineered soil and geosynthetic containment barriers used for liquid and solid waste containment. His research contributions pertaining to the role of diffusion in containment barrier design were recognized in 1995 with the receipt of the Walter L. Huber Civil Engineering Research Prize from the American Society of Civil Engineers (ASCE), and he was recognized in 2013 for his career contributions to the field of environmental geotechnics with the receipt of the inaugural R. Kerry Rowe Honorary Lecture from the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE). He has served as an editor for both the ASCE Journal of Geotechnical and Geoenvironmental Engineering and the Journal of Hazardous Materials published by Elsevier, Amsterdam, and currently serves as an editorial board member of Elsevier's Geotextiles and Geomembranes and as an associate editor of the Canadian Geotechnical Journal. He also was past chair of the Geoenvironmental Engineering Committee (GEC) of ASCE's Geo-Institute, and past co-chair for the Environmental Geotechnics Committee TC215 of the ISSMGE, and currently serves as a member of both the GEC and TC215. His M.S. and Ph.D. degrees in civil (geotechnical) engineering are from the University of Texas at Austin in 1983 and 1988, respectively.

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