Steve A. Mizell

Monitoring Potential Transport of Radioactive Contaminants in Shallow Ephemeral Channels: FY 2012

The U.S. Department of Energy (DOE) National Nuclear Security Administration (NNSA), Nevada Site Office (NSO), Environmental Restoration Soils Activity has authorized the Desert Research Institute (DRI) to conduct field assessments of potential sediment transport of contaminated soil from Corrective Action Unit (CAU) 550, Area 8 Smoky Contamination Area (CA), during precipitation runoff events. CAU 550 includes Corrective Action Sites (CASs) 08-23-03, 08-23-04, 08-23-06, and 08-23-07; these CASs are associated with tests designated Ceres, Smoky, Oberon, and Titania, respectively.

NNSS Soils Monitoring: Plutonium Valley (CAU366) FY2012

The U.S. Department of Energy (DOE) National Nuclear Security Administration (NNSA), Nevada Site Office (NSO), Environmental Restoration Soils Activity has authorized the Desert Research Institute (DRI) to conduct field assessments of potential sediment transport of contaminated soil from Corrective Action Unit (CAU) 366, Area 11 Plutonium Valley Dispersion Sites Contamination Area (CA) during precipitation runoff events. Field measurements at the T-4 Atmospheric Test Site (CAU 370) suggest that radionuclide-contaminated soils may have migrated along a shallow ephemeral drainage that traverses the site (NNSA/NSO, 2009). (It is not entirely clear how contaminated soils got into their present location at the T-4 Site, but flow to the channel has been redirected and the contamination does not appear to be migrating at present.) Aerial surveys in selected portions of the Nevada National Security Site (NNSS) also suggest that radionuclide-contaminated soils may be migrating along ephemeral channels in Areas 3, 8, 11, 18, and 25 (Colton, 1999). In Area 11, several low-level airborne surveys of the Plutonium Valley Dispersion Sites (CAU 366) show plumes of Americium 241 (Am-241) extending along ephemeral channels (Figure 1, marker numbers 5 and 6) below Corrective Action Site (CAS) 11-23-03 (marker number 3) and CAS 11 23-04 (marker number 4) (Colton, 1999). Plutonium Valley in Area 11 of the NNSS was selected for the study because of the aerial survey evidence suggesting downstream transport of radionuclide-contaminated soil. The aerial survey (Figure 1) shows a well defined finger of elevated radioactivity (marker number 5) extending to the southwest from the southernmost detonation site (marker number 4). This finger of contamination overlies a drainage channel mapped on the topographic base map used for presentation of the survey data suggesting surface runoff as a likely cause of the contaminated area. Additionally, instrumenting sites strongly suspected of conveying soil from areas of surface contamination offers the most efficient means to confirm that surface runoff may transport radioactive contamination as a result of ambient precipitation/runoff events. Closure plans being developed for the CAUs on the NNSS may include post-closure monitoring for possible release of radioactive contaminants. Determining the potential for transport of radionuclide-contaminated soils under ambient meteorological conditions will facilitate an appropriate closure design and post-closure monitoring program.

Comparing Playa Inundation Estimates from Landsat and LiDAR Data to a Doppler Radar-Based Hydrologic Model

Although water is a contentious resource in terms of human use and consumption, particularly in the southwestern United States (U.S.), its presence is not always considered valuable or welcome. Where water accumulates on the flat, hard surfaces of desert playas used for the military mission, ephemeral conflict with nature occurs; conflict present only so long as standing water persists into scheduled use for training and testing. Flood occurrences on playas where runways and flightlines are established may incur added financial burden due to unanticipated scheduling changes in training and testing, or damage to infrastructure. The ability to better estimate and predict flooding events including duration and frequency of inundation, which could affect use of playas with infrastructure, may present range managers with a means to avert potential conflicts. For this reason examining the current model that incorporates watershed parameters and Doppler-radar precipitation measurements to estimate runoff onto Rogers (Dry) Lake at Edwards Air Force Base (EAFB), U.S.A. was done. Satellite imagery and digital elevation model data are spatially explicit (associated with a geographic location) and present that advantage both for planning and to provide comparison of model estimates. The degree to which either or both approaches reflect ground condition following storm events was quantified. Pre- and post-standing water extent for the two significant rainfall-runoff events was mapped from Landsat satellite imagery and standing water volume on the playa was then calculated using a high spatial resolution LiDAR–derived digital elevation model (DEM). These results were compared to the runoff volume estimates made from a model that extrapolated precipitation from Doppler-radar and meteorological stations within the Rogers Lake watershed. The results showed both over- and under-estimated playa inundations when compared.

Wind and Water Erosion Potential of Fire-Affected Soils: Immediate and Short- Term Effects in a Desert Ecosystem

The increase in fires in arid and semi-arid parts of the Southwest U.S. has important implications for runoff and sediment management, and for the stewardship of soil-contaminated sites throughout the region. This study was initiated to examine the effects and duration of fire on wind and water erodibility on shrubland sites analogous to those on the Nevada National Security Site. Quantification of wind erosion was conducted with a portable wind tunnel analog and a small, portable rainfall simulator. Data collected on a Coleogyne ramosissima (blackbrush)dominated site indicated post-fire windblown emissions were higher on burned compared to unburned areas, and on vegetative understory soils compared to interspace soils. By 24 months after the fire, these effects were near pre-burn levels. Water erosion, as measured by runoff response and sediment yield, was unaffected by the fire. The same measurements at a Pinus spp. (pinyon)/Artemisia spp. (sagebrush) shrubland site indicated elevated responses in the potential for both wind and water erosion 12 months after a fire. Amounts of airborne particulate material and sediment were higher from vegetative understory soils than interspace soils, while runoff was more prevalent on interspace than understory soils. These differences in wind emission and runoff data highlight the complex relationship between fire and erosion in shrubland ecosystems.

NNSS Soils Monitoring: Plutonium Valley (CAU366)

The U.S. Department of Energy (DOE) National Nuclear Security Administration (NNSA), Nevada Site Office (NSO), Environmental Restoration Soils Activity has authorized the Desert Research Institute (DRI) to conduct field assessments of potential sediment transport of contaminated soil from Corrective Action Unit (CAU) 366, Area 11 Plutonium Valley Dispersion Sites Contamination Area (CA) during precipitation runoff events.

Using Doppler Radar Precipitation Measurements to Enhance Estimates of Playa Inundation

In the hydrologic approach developed by French et al. (2005) to estimate the 100-year regulatory floodplain on a playa lake, it was conservatively assumed that precipitation varies with elevation but is otherwise uniform over the entire contributing watershed. In this follow-on study, Doppler radar (WSR-88D) precipitation estimates were used to incorporate spatial variability of precipitation and to validate the approach for the Rogers Lake watershed in the California Mojave Desert, USA. Accurate runoff estimates are necessary to manage mission activities for Edwards Air Force Base, which lies within this watershed, because Rogers (dry) Lake playa is used as an active runway. Radar-measured storm events were analyzed using the French et al. (2005) approach and the modeled volume of runoff reaching Rogers Lake was compared to its inundation calculated based on corresponding Landsat satellite imagery and airborne LiDAR high spatial resolution digital elevation model (DEM) data of the lakebed. Model results both under- and over-estimated playa inundations compared to the image based DEM calculations for each of the two storm events analyzed. Possible explanations of the differences include: (1) poor representation of ground level precipitation provided by the Doppler data; (2) over or underestimation of water via image interpretation; (3) inappropriate estimation of the watershed hydrologic parameters ( e.g. , infiltration); (4) error associated with the data sources, particularly in the DEM; and (5) a combination of one or more of these factors.