Transport of anthropogenic uranium from sediments to surface waters during episodic storm events

Remobilization of sediment-associated uranium (U) from contaminated floodplain sediments to a stream adjacent to a nuclear weapons processing facility during episodic rain events was investigated. In addition, U solid phase associations in suspended sediments were assessed by a sequential chemical extraction procedure to gauge U chemical lability. Mass flux estimates determined from base flow measurements potentially underestimate the amount of U transported from contaminated terrestrial sources to surface water systems. Erosional processes can effectively mobilize sediment-associated contaminants during storms or flooding. During the various storm events measured, approximately 1500 to 2800% more U was exported to Upper Three Runs Creek (UTRC) relative to base Row measurements. Sequential extraction results suggest the suspended sediment load transports the bulk of U in labile forms predominantly as acid soluble (specifically adsorbed), MnO2 occluded and organically bound phases. This implies that U may be available to the ecosystem under a range of environmental conditions likely to be encountered within depositional environments (e.g., Eh and pH) or as a result of industrial processes. This study demonstrates the need to evaluate contaminant transport during storm events from exposed contaminated sediments, or from industrial waste stockpiles subject to erosion.