Jennifer Nyman, PhD, PE (California), coauthored “Modeling evaluation of the impact of residual source material on remedial time frame at a former uranium mill site.” The paper was published in the February 2024 edition of the Journal of Containment Hydrology.

Jennifer’s coauthors are Ronald Kent, Raymond Johnson, and Alan Laase from RSI EnTech, LLC.

Jennifer is a Senior Principal based in California with more than 17 years of experience focused on the characterization and remediation of soil and groundwater. She has experience in strategic environmental consulting, support to counsel, and applied research.

This study of a former uranium mill in the southwestern United States reveals that groundwater contamination from uranium processing sites persists longer than originally thought. Significant residual uranium mass can remain even after tailings have been removed. The findings emphasize the need for accurate forecasted remedial time frames to manage risks and costs and support effective site reuse.

The Journal of Contaminant Hydrology is an international journal that publishes scientific articles to enhance understanding of water resource contamination. It focuses on the physical, chemical, and biological processes influencing the fate of organic and inorganic contaminants and addresses ecological consequences.

Abstract

Groundwater contamination at legacy uranium processing sites is an ongoing global challenge. Plumes at many uranium-contaminated sites are more persistent than originally predicted by groundwater modeling. Previous investigations of uranium plume persistence identified residual and secondary sources that contribute to plume longevity, but there is a remaining need to revise forecasted cleanup times using information about these ongoing sources. The purpose of this study is to investigate the quantitative impact of residual vadose-zone sources of uranium on groundwater remediation time frame. This objective was approached by applying numerical uranium transport simulations and uncertainty analysis to a former uranium mill site in the southwestern United States. Information from recent site investigations provided details about the distribution and release characteristics of uranium accumulations in the vadose zone. The residual uranium characteristics were incorporated as decaying source terms in the transport model. A stochastic approach using an iterative ensemble smoother was applied for history matching, and the transport model was used to assess the impact of multiple remedial alternatives on forecasted time frame. The forecasted time frame to achieve the groundwater remediation goal for uranium by monitored natural attenuation is around thousands of years, and treatment of the dissolved plume does not reduce the projected time frame. The large proportion of residual uranium mass remaining in the vadose zone and the gradual leaching rate due to the site’s semiarid climate create a long-lived source that can sustain a dissolved plume for thousands of years despite an estimated 99% mass removal achieved during mill tailings disposal. Residual uranium in vadose-zone sediments beneath former tailings impoundments could present comparable uranium-plume persistence and remediation challenges at other legacy uranium mill sites in semiarid climates. Other remaining uranium-impacted sites are similarly complex, and forecasted remedial time frames are needed to effectively achieve compliance, manage risk, assess the benefits of additional treatment, manage and project costs, and support beneficial site reuse.

More Information

Learn more about the article: Modeling Evaluation of the Impact of Residual Source Material on Remedial Time Frame at a Former Uranium Mill Site
Learn more about the journal: Journal of Containment Hydrology
For consultation regarding soil and groundwater remedies, contact Jennifer at JNyman@Geosyntec.com.
Learn more about Jennifer: Jennifer Nyman | LinkedIn