Historical Case Analysis of Uranium Plume Attenuation (NUREG/CR-6705)

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Publication Information

Manuscript Completed: January 2001
Date Published: February 2001

Prepared by:
C.F. Jove Colon, P.V. Brady, M.D. Siegel, E.R. Lindgren

Sandia National Laboratories
Albuquerque, NM 87185-0750

E. O'Donnell, NRC Project Manager

Prepared for:
Division of Regulatory Applications and Analysis
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

NRC Job Code W6811

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Abstract

Groundwater plumes containing dissolved uranium at levels above natural background exist adjacent to uranium ore bodies at uranium mines, milling locations, and at a number of explosive test facilities. Public health concerns require that some assessment of the potential for further plume movement in the future be made. Reaction-transport models, which might conceivably be used to predict plume movement, require extensive data inputs that are often uncertain. Many of the site-specific inputs are physical parameters that can vary spatially and with time. Limitations in data availability and accuracy mean that reaction-transport predictions can rarely provide more than order-of-magnitude bounding estimates of contaminant movement in the subsurface. A more direct means for establishing the limits of contaminant transport is to examine actual plumes to determine if, collectively, they spread and attenuate in a reasonably consistent and characteristic fashion. Here a number of U plumes from ore bodies and contaminated sites were critically examined to identify characteristics of U plume movement.

The magnitude of the original contaminant source, the geologic setting, and the hydrologic regime were rarely similar from site to site. Plumes also spanned a vast range of ages and no complete set of time-series plume analyses exist for a particular site. Despite the accumulated uncertainties and variabilities, the plume data set gave a clear and reasonably consistent picture of U plume behavior. Specifically, uranium plumes:

• Appear to reach steady-state, that is, they quit spreading rapidly (within a few years).
• Exceed roughly 2 km in length only in special cases e.g. where in situ leaching has been carried out. The majority is much smaller.
• Exhibit very similar U chemistry between sites. This implies analogous contaminant attenuation mechanisms despite their location.