Results of a 2-D surface electrical resistivity survey of a 300-m transect across the 300 Area uranium plume near the Hanford IFC. Resistivity response increases from dark blue, to green, to orange, to red. Coarse, dry sediments show high resistivity while fine-textured, water-saturated sediments show low resistivity. Backfill exists in the red zone, the water table occurs at yellow, the Hanford-Ringold contact at light blue, and finer-textured Ringold sediments appear as dark blue and black. The geophysical measurements reveal significant subsurface structure (@60-120 m and 140-240) that are interpreted as erosional channels in the Hanford-Ringold contact. Such measurements are essential to define the lateral connectivity and spatial features of transition zones and hydrogeologic structures that control contaminant migration.
The SFA is focusing on the subsurface behavior of U, 99Tc, and Pu, all of which are risk drivers at the Hanford Site. Uranium and 99Tc have environmental mobility and persistence, while Pu has lower mobility but is highly radioactively toxic.
The inventory of the three contaminants is significant: 202,703 kg of U, 400 kg of P, and 99Tc at 1309 Ci. Each contaminant can adopt multiple valence states in the environment depending on the redox potential, concentrations of microbial electron donors and acceptors, and the presence and types of agents that can facilitate electron transfer reactions.
The three contaminants have complex biogeochemistry and have been sources of long-term concerns and scientific issues. They provide important scientific opportunities for advancing the subsurface science field and support Hanford Site remediation and closure.