SREL Reprint #1924





Actinide Association with Groundwater Colloids in a Coastal Plain Aquifer

By D. I. Kaplan1, P. M. Bertsch2, D. C. Adriano2 and K. A. Oriandini3

Division of Biogeochemistry, Savannah River Ecology Laboratory, The University of Georgia, Aiken, SC 29802
1is currently at Battelle, Pacific Northwest Laboratories, Transport Geochemistry Group, MSIN K6-81, Box 999, Riceland, WA 99352
2Division of Biogeochemistry, Savannah River Ecology Laboratory, The University of Georgia, Aiken, SC 29802
3Argonne National Laboratory, Environmental Research Division, Argonne, IL 60439


Trace levels of Pu, Am, Cm, and U in an acidic plume have been traveling through a surface aquifer underlying the Savannah River Site, Aiken, SC, at rates appreciably greater than anticipated. The objective of this study was to determine the extent to which each of these actinides was associated with groundwater colloids, a potential cause for the apparent enhanced transport. Contaminated groundwater was recovered along a 1.02km transect at approximately the rate of groundwater flow, passed though an ultrafiltration system, and then chemically characterized. The filterable (>500 molecular weight) fraction of nuclides increased with reported nuclide distribution coefficients (Kd values): Pu > Th > U > AM = Cm > Ra > tritium. The filterable fractions of the stronger sorbing nuclides (Pu and Th) increased, whereas those of the weaker-sorbing nuclides (Am, Cm, and Ra) generally decreased with increasing pH (3.4 to 4.0) and distance from the point source. Uranium was equally divided between the dissolved and filterable fractions throughout the transect. At the farthest sampling point in the contaminant plume (0.55 km), all the Pu and Th and none of the Am and Cm were in the filterable fraction. Plutonium appears to have a much greater potential than Am or Cm for moving through the study site in association with mobile colloids. However, Am and Cm pose a much greater threat than Pu of migrating through this system, because almost all of the Pu and relatively little of the Am and Cm were retained by the matrix.

SREL Reprint #1924

Kaplan, D.I., P.M. Bertsch, D.C. Adriano, and K. Orlandini. 1994. Actinide association with groundwater colloids in a coastal plain aquifer. Radiochimica Acta 67/67:181-187.

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