HR: 1330h
AN: H32A-0541    [PDF]
TI: Plume-Scale Testing of a Simplified Method for Detecting Tritium Contamination in Plants and Soil
AU: * Andraski, B J
EM: andraski@usgs.gov
AF: U.S. Geological Survey, 333 West Nye Lane, Room 203, Carson City, NV 89706 United States
AU: Halford, K J
EM: khalford@usgs.gov
AF: U.S. Geological Survey, 333 West Nye Lane, Room 203, Carson City, NV 89706 United States
AU: Johnson, M J
EM: johnsonm@usgs.gov
AF: U.S. Geological Survey, 333 West Nye Lane, Room 203, Carson City, NV 89706 United States
AU: Michel, R L
EM: rlmichel@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, MS-434, Menlo Park, CA 94025 United States
AU: Radyk, J C
EM: jradyk@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road, MS-434, Menlo Park, CA 94025 United States
AB: Research at the Amargosa Desert Research Site near Beatty, Nevada indicates that tritium movement from a closed low-level radioactive waste facility occurs primarily in the gas phase with preferential transport through coarse-textured sediment layers. However, models for movement of tritiated water vapor at the site fail to predict the extent of transport indicated by field measurements. In order to develop a better understanding of the spatial distribution of tritium contamination in the near-surface environment adjacent to the waste facility, a recently published tritium contamination-detection method was tested for collection and analysis of plume-scale data. The method entails solar distillation of plant water from foliage, followed by filtration and adsorption of scintillation-interfering constituents on a graphite-based solid-phase-extraction column prior to direct-scintillation counting. Samples were collected from 103 plants (creosote bush; {\it Larrea tridentata}) within a 72-ha area adjacent to the waste facility. Plant data showed elevated tritium concentrations up to 300 m from the waste facility. For a small ($\sim$ 8 ha) area where high-density soil-water vapor data were already available, plant-based and soil-based concentration contours compared favorably. Plant data for previously unmeasured areas identified "hot spots" that were later verified by direct soil measurements. Regression analysis of tritium concentrations from collocated plant- and soil-sampling sites showed that empirical relations could be developed to predict soil concentrations (y) from the more simply determined plant concentrations (x): e.g., the equation for root-zone soil concentrations (Bq/L) was y = 1.156 x + 55.17 (r$^{2}$ = 0.9521; SEE = 250). Results of this work have improved knowledge of the extent of tritium contamination in the near-surface environment. The pattern of the tritium concentrations indicated that the observed contamination originates from two sources--the waste-burial trenches and surface spills inside the waste facility. A study is now underway to estimate the flux of tritium from the subsurface to the atmosphere. The approach includes a combination of (i) periodic measurement of tritium concentrations in soil, plants, and air at selected sites, (ii) mapped tritium distributions, and (iii) continuous measurement of evapotranspiration.
UR: http://nevada.usgs.gov/adrs/
DE: 1875 Unsaturated zone
DE: 1894 Instruments and techniques
SC: Hydrology [H]
MN: 2003 Fall Meeting