HR: 0830h
AN: H51D-1104    [PDF]
TI: Predicting the Surface Redistribution of Possibly Contaminated Tephra Deposits at the Yucca Mountain Repository Using Cesium-137
AU: Harrington, C D
EM: charrington@lanl.gov
AF: Los Alamos National Laboratory, EES-9 MS J521, Los Alamos, NM 87545-0001 United States
AU: Whitney, J W
EM: jwhitney@usgs.gov
AF: U.S. Geological Survey, Federal Center MS 980, Denver, CO 80225 United States
AU: * Ebert, K
EM: teryne@hotmail.com
AF: Los Alamos National Laboratory, EES-9 MS J521, Los Alamos, NM 87545-0001 United States
AB: In the event a volcanic eruption occurred through the proposed Yucca Mountain repository, Nevada, radioactive waste particles could be incorporated into the eruption products and deposited with the volcanic ash. The objective of this study was to predict the surface redistribution of the contaminated tephra deposits in order to evaluate how the critical group (located 20 km south of the repository within the Fortymile Wash drainage area) might be affected. We calculated the volume of material that has been eroded or deposited within the past ~50 years using cesium (Cs)-137. Radioactive Cs-137 was distributed worldwide as a result of atmospheric nuclear weapons tests during the 1950's, and has been used as an anthropogenic tracer. In most earlier cesium-137 studies, the investigated sites were either along several transects or on plots of a few dozen km2, whereas this study covers an area of $>$1500 km2. Fortymile Wash is an 800-km2 drainage basin that includes the entire eastern slope of Yucca Mountain and the Fortymile Wash alluvial fan; therefore, understanding the surface processes along Fortymile Wash are important to the volcanic-eruption consequence. To assess erosion rates on the Fortymile Wash fan, alluvium samples were analyzed for Cs-137 concentrations, for the vertical cesium profile down to ~10 cm depth, and for particle-size composition of the upper 3-5 cm. The results of Cs-137 concentrations in the samples from the upper fan indicate that the upper fan interstream divide areas have been eroding over the last 50+ years and have lost 1 cm to 2 cm of the upper soil horizon, mainly as the result of eolian processes.
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 8404 Ash deposits
SC: Hydrology [H]
MN: 2003 Fall Meeting