Movement of Ruthenium in the Bed of White Oak Lake

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Abstract
Currently, a few thousand c/year of ruthenium flow onto the bed of former White Oak Lake from the Oak Ridge National Laboratory's intermediate-level waste pits. As the waste water traverses the lake bed a significant portion of the ruthenium is removed from solution. The ruthenium that is not sorbed on the lake-bed soil drains into White Oak Creek, a tributary of the Clinch River. An investigation was made to determine the quantity and distribution of ruthenium in the soil of the lake bed and to identify and define geoghydrological factors affecting the movement of ruthenium through the lake bed. As of February 1962, the lake bed contained approximately 1200 c of ruthenium. The ruthenium is present mainly in two tracts of contamination, covering approximately 10 acres, that coincide roughly with the surface flow of waste over the bed. The highest concentrations of ruthenium occur in the uppermost few in. of the lake bed and about 70 per cent of the activity is in the top 2 ft of soil. The lake bed is underlain by a thin layer of recent lacustrine sediment, several ft of alluvium and the Conasauga shale formation of Cambrian age. Water-level measurements indicate that the depth to ground water varies from <1 to 5 ft below the surface. The subsurface migration of ruthenium follows closely the paths indicated by water-table contours. The rate of groundwater movement in the upper 2 ft of soil varies from 1 to 5 ft/day, while movement in the material 2–5 ft below the surface ranges from 0.05 to 0.25 ft/day. Thus, the maximum rate at which ruthenium may travel in the upper layers of soil is approximately twenty times that of the lower layers. Ruthenium is transported to White Oak Creek by surface water and ground water moving over and through the bed of White Oak Lake. Only a small fraction of the ruthenium is transported by ground water through the lake-bed soil into the creek. The ruthenium moves at such a slow rate through the soil that radioactive decay reduces the concentration of that reaching the creek by subsurface movement to insignificant proportions. The amount of surface flow and, consequently, the quantity of ruthenium that reaches the creek from the lake bed varies seasonally. During the dry summer months drainage from the waste pits recharges the ground water in the lake bed and thus there is little surface flow and, consequently, little ruthenium that flows into White Oak Creek. However, in the wet winter season surface runoff from the lake bed is high and therefore larger amounts of ruthenium enter White Oak Creek.

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