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Reducing Uranium in a Contaminated Aquifer

Source: Ken Williams, Dan Hawkes

Williams_longThe capacity for subsurface sediments to sequester radionuclide contaminants, such as uranium (U), and retain them after bioremediation efforts are completed is critical to the long-term stewardship of remediated sites. In U bioremediation strategies, carbon amendment stimulates bioreduction of U(VI) to U(IV), immobilizing it within the sediments. Sediments enriched in natural organic matter are naturally capable of sequestering significant U, but may serve as sources to the aquifer, contributing to plume persistence.

A team of scientists including ESD’s Ken Williams and Phil Long recently compared two types of organic-rich sediments to better understand U release mechanisms. Sediments that were artificially primed for U removal were retrieved from an area previously biostimulated, while detrital-rich sediments were collected from a location never subject to amendment. Batch incubations demonstrated that primed sediments rapidly removed uranium from the groundwater, whereas naturally reduced sediments released a sizeable portion of U before U(VI)-reduction commenced.

These investigations stress the importance of characterizing zones with heterogeneous carbon pools at U-contaminated sites prior to the determination of a remedial strategy, to identify areas which may contribute to long-term sourcing of the contaminants.

Fig. 1. Conceptual layout of the Winchester-Big Rusty experimental array at Rifle IFRC site in Colorado. Sediment core and groundwater sampling locations discussed in the text are denoted with stars and open circles.

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Citation:  Mouser, P.J., L.A. N’Guessan, N.P. Qafoku, M. Sinha, K.H. Williams, M. Dangelmayr, C.T.  Resch, A. Peacock, Z. Wang, L. Figueroa, and P.E. Long (2014), Influence of carbon and microbial community priming on the attenuation of uranium in a contaminated floodplain aquifer. Ground Water, DOI: 10.1111/gwat.12238.

Funding Source: BER, SS SFA, Rifle IFRC