HR: 1330h
AN: H13B-07    [Abstracts]
TI: Fate and Transport of CL-20 and RDX in Unsaturated Laboratory Columns
AU: * LeMond, L A
EM: llemond@email.arizona.edu
AF: University of Arizona Department of Soil, Water, and Environmental Science, P.O. Box 210038, Tucson, AZ 85721-0038 United States
AU: Gamerdinger, A P
EM: apg1@email.arizona.edu
AF: University of Arizona Department of Soil, Water, and Environmental Science, P.O. Box 210038, Tucson, AZ 85721-0038 United States
AU: Szecsody, J E
EM: jim.szecsody@pnl.gov
AF: Pacific Northwest National Laboratory, P.O. Box 999 K3-61, Richland, WA 99354 United States
AB: This research examines the fate and transport of two explosive compounds, Hexanitrohexaazaisowurtzitane (CL-20) and Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in unsaturated laboratory columns. The transport and fate of these compounds were studied under saturated and unsaturated conditions in three natural soils: coarse sand, sandy loam, and a silt loam. Unsaturated column experiments were conducted using an ultra-centrifugation method. Sorption and degradation parameters were determined by moment analysis and hydrodynamic parameters were assessed with a two-region flow model. Differences in these parameters were evaluated as a function of water content. The fate and transport of CL-20 is highly dependent on 1) the soil type and 2) the compound's residence time in the soil and 3) water content of the media. Sorption of CL-20 was rate-limited. CL-20 degradation in saturated columns produced a half-life of as much as 22hr, but in unsaturated columns the degradation rate increased considerably, producing a half life of as little as 2hr. The fate and transport of RDX are also affected by the soil type, but sorption appeared to be instantaneous. Degradation of RDX was negligible. Our results suggest that at very low water content immobile water regions may become (at least in effect) isolated water regions and significantly alter the retardation of the tracer. In the sandy loam, there was as much as a 20-fold over-prediction of the retardation factor in the unsaturated saturated columns when predicted by Kd values derived from saturated columns. In the coarse sand, Kd values derived from saturated columns over-predicted retardation in the unsaturated columns by as much as 30%. In the silt loam, retardation factors were over-predicted by as much as 80%. At very low water contents, predictions of tracer behavior become very difficult because of changes in the flow regime that cannot be directly accounted for.
DE: 1803 Anthropogenic effects
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
DE: 1875 Unsaturated zone
SC: Hydrology [H]
MN: 2005 Joint Assembly