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Webinar – Enhancing Armored Final Covers for Radioactive Waste Disposal Facilities Through Naturalization -Wednesday, August 17, 2022

Enhancing Armored Final Covers for Radioactive Waste Disposal Facilities Through Naturalization
Dr. Craig H. Benson
Wisconsin Distinguished Professor Emeritus
CRESP/University of Wisconsin-Madison

Webinar Slides
Webinar Video

Wednesday, August 17, 2022
1:00-2:30 p.m. Eastern Time

Abstract:  A 14-year field experiment was conducted to evaluate different management strategies for rock-armored earthen final covers used for disposal facilities in semiarid and arid environments.  A facility with two different test areas was constructed at DOE’s Grand Junction Disposal Facility with the same earthen materials and methods employed for the final cover at full scale.  Both test areas contained a large (10 × 20 m) instrumented drainage lysimeter to monitor the water balance of the cover at field scale.  Herbicide was applied to the surface of both test areas to preclude vegetation for the first 7 years, simulating conventional practices used by DOE.  After 7 years, active management including herbicide application ceased on one test area, allowing vegetation to establish and the cover to “naturalize.”  Treatment of the other (“conventional”) test area continued as before.  Percolation rates increased in both test areas during the initial 7 years as the test sections weathered in the environment.  Percolation rates ranging from 10–47 mm/yr were measured in wetter years, considerably higher than anticipated (3 mm/yr).  Increases in saturated hydraulic conductivity of the protection layer and the radon (Rn) barrier contributed to the higher percolation rates.  Ceasing herbicide application in the naturalized test area had a profound effect on the hydrology.  As vegetation established, evapotranspiration increased, water contents in the protection layer and radon barrier decreased systematically, and the percolation rate decreased significantly (to near zero).  In contrast, the conventional test area continued as before, with elevated water contents and high percolation rates in wet years.  The study demonstrated that allowing armored covers to naturalize results in superior performance, while reducing maintenance efforts and costs.


About the speaker:  Dr. Craig Benson is a geoenvironmental engineer with expertise in waste management, waste containment systems, recycling and beneficial reuse, and sustainability.  He is currently a Distinguished Professor Emeritus at the University of Wisconsin-Madison.  He previously served as the Dean of Engineering at the University of Virginia and as Department Chair and Director of Sustainability Research and Education at the University of Wisconsin-Madison.  Dr. Benson has been conducting research related to environmental protection for three decades, mainly focusing on environmental containment of solid, hazardous, radioactive, and mining wastes; the beneficial use of industrial byproducts; and sustainable infrastructure.  He is recognized as an international authority on waste containment systems and has published more than 300 refereed articles.  Dr. Benson has made important contributions to the U.S. Department of Energy, particularly through his leadership of the DOE Landfill Partnership (in association with CRESP, the Consortium for Risk Evaluation with Stakeholder Participation, led by Vanderbilt University).  He has also contributed significantly to other federal agencies, authoring guidance on evapotranspiration covers for the U.S. Environmental Protection Agency and developing U.S. Nuclear Regulatory Commission guidance for the engineering properties of final covers for waste containment.


The Department of Energy’s Performance and Risk Assessment Community of Practice (PRACOP) focuses on sharing knowledge, best practices, and lessons learned related to performance assessments and risk assessments, particularly for DOE sites.  These assessments are critical for:

  • management (design, operation, and closure) of disposal facilities, including landfills or near-surface disposal facilities
  • waste form development and implementation
  • closure of tanks and waste sites
  • in situ deactivation and decommissioning
  • soil and groundwater remediation.


PRACOP meetings and webinars are open to interested parties from federal, state, tribal, contractor, stakeholder, and academic organizations involved in DOE performance assessment or risk assessment activities.  Those who would like to be added to or removed from the distribution list should send their name and email address to  The PRACOP website is at, where archived materials are available.