HR: 1330h
AN: H32A-0505    [PDF]
TI: Carbon-14 Phase Partitioning and Transport in Unsaturated Sediments
AU: * Fox, D
EM: foxdt@inel.gov
AU: Plummer, M
EM: plumma@inel.gov
AU: Hull, L
AB: Wastes buried at the Radioactive Waste Management Complex (RWMC) of the Idaho National Engineering and Environmental Laboratory (INEEL) include activated metals that release radioactive $^{14}$C as they corrode. To better understand $^{14}$C phase partitioning and transport in the RWMC sediments, we conducted a series of transport experiments using $^{14}$C (radio-labeled sodium carbonate) and non-reactive gas-phase (sulfur hexafluoride) and liquid-phase (bromide and tritiated water) tracers in a large (2.6-m high by 0.9-m diameter) sediment column. Steady-state unsaturated flow was established prior to injecting tracers into the column. Tracer migration was monitored in pore-water and pore-gas samples taken from co-located suction lysimeters and gas ports. One year after the $^{14}$C injection, the column was cored and solid-phase $^{14}$C activity was measured. $^{14}$C measurements provide an average liquid-gas partition coefficient (Henry's law constant) of 4.0, an average liquid-solid partition coefficient (K$_{D}$) of 0.2 mL/g, and an activity mass balance of $\sim$94% (i.e., percent of injected $^{14}$C). These determinations are consistent with values of the Henry's law constant (4 to 13) and K$_{D}$ (0.4 mL/g) estimated prior to measurement of solid phase $^{14}$C activity. The relatively good agreement between measured and estimated K$_{D}$ values suggests the ability to estimate $^{14}$C behavior, in the current system, based solely on liquid- and gas-phase activity measurements. The low partition coefficient values suggest that transport is effectively controlled by gas diffusion with minimal retardation by partitioning onto the solid phase, and little long-term retention. The implication for the RWMC is that $^{14}$C released via corrosion of activated metals is primarily transported to underlying ground water and overlaying atmosphere in the gas-phase, rather than via downward liquid transport as was assumed by recent performance evaluation studies.
UR: http://www.inel.gov/esra/02portfolio/mesocarbon.shtml
DE: 1099 General or miscellaneous
DE: 1832 Groundwater transport
DE: 1875 Unsaturated zone
SC: Hydrology [H]
MN: 2003 Fall Meeting