Uranium present at the DOE Savannah River Site has remained relatively confined to the Tims Branch wetlands following a series of release events 70 years ago totaling 43,000 kg uranium released. Following field sampling events to discern where hotspots were located, sequential extraction analysis of soil cores provides evidence towards the associated phases of the majority of the uranium. Redox gradients in wetland environments increase the transience of uranium mobility, leading to accumulation in portions of the wetland that do not facilitate transport of this redox-active radionuclide. Of particular interest are the solid phase—predominantly iron oxide minerals in the subsurface of southwestern South Carolina—and the organic phase—an association with rich organic matter available throughout wetland environments. SEM imaging and Electron Dispersive X-Ray Spectroscopy (EDS) analysis indicate that uranium has coated certain soil particles in concentrations of up to 16%, by weight percent. Further, aerial gamma detection and field ground-truthing of aerial data has begun to identify where uranium accumulation has occurred most severely within Tims Branch, providing an initial lateral account of the uranium mass in the wetland. To corroborate this lateral uranium accountancy, sequential extraction of various uranium phases as a function of depth in core samples allows for a calibration of future flyover measurements and a picture of the distribution within the wetland, both as an initial mass balance and for the identification of phase affinities. Deposition in the sediments and wetland transport, with respect to iron and carbon redox cycling, are being studied using these ex situ chemical analyses and in situ radiation detection measurements, providing an initial summary of uranium phases dominant in Tims Branch wetlands, association with fluxes of redox-active nutrients, and the water quality currently leaving this section of the watershed.

Wetland uranium distribution within Tims Branch at the Savannah River site

2019 Fall National Meeting

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