Multiyear Analysis of the Fate and Transport of Contaminated Soils at Plutonium Valley and the Smoky Site, Nevada National Security Site
- Desert Research Inst. (DRI), Las Vegas, NV (United States)
Desert Research Institute (DRI) has collected approximately 10 years of atmospheric and hydrologic data at Plutonium Valley and the Smoky Site on the Nevada National Security Site to identify the potential for radionuclide-contaminated soils to be transported via wind and water. Plutonium preferentially binds to finer soil particles (Shinn et al., 1993; Miller et al., 2015), which can be transported through erosion processes. Data collected by DRI are used to determine the mechanisms and thresholds that result in the transport of radionuclide-contaminated soils, and climate model projections are used to understand how these mechanisms may change in the future. This work will help identify the parameters and threshold conditions that should be incorporated into post-closure monitoring plans for these and other Soils Corrective Action Unit (CAU) sites. The most influential meteorological quantities for aeolian sediment transport are wind speed, soil moisture, and relative humidity. Wind-induced turbulence suspends sediment in the air. Precipitation dislodges compacted sediment upon impact, which makes it more easily eroded by wind. Drier soils are more easily eroded by wind because soil moisture binds sediment to water molecules and more energy is required to dislodge the soil particles. Atmospheric moisture affects the partitioning of friction forces at the surface responsible for dust production, and dust production is highest within a site-specific relative humidity range. Elevated airborne dust conditions due to local dust production are likely for 10-minute average wind speeds in excess of ~24 kilometers per hour (km/h) (15 miles per hour [mph]) with relative humidity between 5 percent and 40 percent over dry soil. Elevated dust conditions are most frequent in summer and least frequent in the winter. Based on climate model projections, both wind speed and soil moisture are expected to decrease by the end of the century, but each will have an opposite effect on dust production. During summer, dust events will likely become more frequent because of decreased soil moisture in response to substantially increased temperatures and only minor changes in the frequency of high wind events. During the other seasons, dust events are expected to be less frequent. Aerial surveys show elevated radionuclide concentrations extending downstream in channels from plutonium dispersal test locations within Plutonium Valley, suggesting that channelized flow is a mechanism by which radionuclides are transported in this area (Colton, 1999; Nikolich et al., 2019). Precipitation can induce channelized flow, which suspends and transports sediment at a rate proportional to the flow rate and turbulence. Measurable streamflow is recorded at Plutonium Valley and the Smoky Site on 50 percent of days with precipitation totaling at least 2.5 millimeters (mm) (0.1 inch [in]). Streamflow in excess of three feet per second (fps) is capable of transporting fine sediment (Garcia [ed.], 2008), and occurs at the Smoky Site flume on 50 percent of days with ~25 mm (1 in) of precipitation measured at the Smoky Site meteorological station. Based on climate model projections, the frequency of runoff-generating events is expected to increase in the summer because of increased monsoon activity and to decrease in the spring and fall at Plutonium Valley and the Smoky Site by the end of the twenty-first century. Winter changes to streamflow frequency are uncertain because of the competing factors of slightly increased precipitation frequency and higher evaporative demand, and therefore require more precipitation to saturate the soil to produce streamflow. The frequency of events generating streamflow with flow rates sufficient to transport sediment is expected to increase. Projected higher-intensity extreme events will likely lead to higher flow rates during individual storms. In channelized flows, higher flow rates result in higher sediment yield. Therefore, redistribution of sediment becomes more likely and leaves more contaminants exposed to resuspension by wind during the dry season.
- Research Organization:
- Desert Research Inst. (DRI), Reno, NV (United States)
- Sponsoring Organization:
- USDOE Office of Environmental Management (EM)
- DOE Contract Number:
- DE-NA0003590
- OSTI ID:
- 1576552
- Report Number(s):
- DOE/NV/0003590-44
- Country of Publication:
- United States
- Language:
- English
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