MINERALOGY OF ANTHROPOGENIC URANIUM IN RESERVOIR SEDIMENTS AND IMPLICATIONS FOR URANIUM TRANSPORT AND BIOGEOCHEMISTRY

Between 1958 and 1982, a large quantity of depleted uranium (DU) was released into the atmosphere around the National Lead Industries (NLI) uranium munitions processing plant located in Albany, New York. Within a 600-m radius of the plant, ~3500 kg of DU were deposited as µm-size aerosols, creating a significant exposure risk by inhalation to plant workers and nearby residents. Lesser quantities of DU were released into surface and groundwater.

Sediments of Patroon Reservoir, located ~ 1 km downstream and downwind from the plant, contain a detailed record of uranium deposition. The sediments are anoxic, were deposited at a rate of ~ 6 cm per year, and consist mainly of quartz, mixed-layer clays, and organic matter with grain sizes ranging from fine sand to clay. Uranium occurs in the sediments as anhedral grains, <1 to 30 µm in diameter with a mean diameter of 5 µm, and morphologies ranging from compact, equant grains to spongy, multi-grain aggregates. The majority of grains consist of U + Si (±Ca) compounds with low microprobe analysis totals and are inferred to be hydrous uranyl- oxy-hydroxides and silicates. A few grains were observed to be nearly stoichiometric UO₂, the presumed original composition of the aerosols. In some cases, the U particles are too large relative to the matrix grains to be hydrodynamically equivalent, implying that they were emplaced by direct atmospheric deposition or formed by precipitation from the aqueous phase. In other cases, U particle size is consistent with fluvial transport and deposition. Major goals of our ongoing work are 1) to use uranium mineralogy of the sediments to place constraints on the pathways and kinetics of UO₂ alteration under reducing conditions such as found in the reservoir; and 2) to better characterize the morphology and composition of the original aerosol particles to inform atmospheric dispersion and inhalation dosimetry modeling studies.