Julianne J. Miller

Flood hazard identification and mitigation in semi- and arid environments

Alluvial fans are ubiquitous geomorphological features that occur throughout the world, regardless of climate, at the front of mountains as the result of erosion and deposition. They are more prominent in semi- and arid climates simply because of the lack of vegetative cover that masks their fan shapes in more humid areas. From both engineering and geological viewpoints, alluvial fans present particular fluvial and sedimentation hazards in semi- and arid regions because episodic rainfall-runoff events can result in debris, mud, and fluvial flows through complex and, in some cases, migratory channel systems. Further, in semi- and arid climates alluvial fans often end in terminal or playa lakes. Given the uniform topography of playa lakes, these features often present ideal locations for facilities such as airports; however, regardless of the engineering advantages of the topography, the episodic and often long-term flooding of these lakes attracts migratory birds. The purpose of this volume is to summarize the current state-of-the-art, from the viewpoint of engineering, in the identification and mitigation of flood hazard on alluvial fans; and to accomplish this a fundamental understanding of geology is required.

Characterizing potential exposure to the public from low-level radioactive waste transportation by truck

To address public concern about potential exposure to gamma radiation from legal-weight low-level radioactive waste truck shipments to the Nevada Test Site, a stationary, automated array of four pressurized ion chambers was established for trucks to pass through. Data were collected from 1,012 of the 2,260 trucks that transported low-level radioactive waste to the Nevada Test Site from February through December 2003. To avoid perception of biasing a potential exposure low, the maximum reading (&mgr;R per hour; &mgr;R h−1) from the array was assigned as the gross measurement value for each truck. [In this article, exposure measurements are reported as Roentgen (R), as this unit is consistent with the data readings of the measurement instruments and has been historically presented to public stakeholders. Subsequently, dose measurements are reported as Roentgen Equivalent Man (rem).] To calculate the “net exposure” for each truck, the average and standard deviation of the maximum background values during the corresponding 12-h period when the truck arrived were subtracted from the gross value. For 483 trucks (47.7%), calculated net exposure values were equal to or less than zero, indicating that the exposure from the truck was indistinguishable from background. An additional 206 trucks (20.4%) had calculated net exposure values ranging between 0.0 and 1.0 &mgr;R h−1. Cumulative exposure scenarios appropriate for rural transportation routes to the Nevada Test Site were developed; however, these scenarios assumed the unlikely case that the same individual was exposed to all of the trucks on that route. Cumulative exposure values were dominated by a small percentage of the trucks with comparatively high values. In communities along transportation routes, the probability of an individual receiving a potential exposure from a single truck may be a more meaningful perspective.

EL NINO - LA NINA IMPLICATIONS ON FLOOD HAZARD MITIGATION

The effects of El Nino and La Nina periods on the maximum daily winter period depths of precipitation are examined using records from five precipitation gages on the Nevada Test Site. The potential implications of these effects are discussed.

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.

High Density Metal Contaminant Transport in Arid Region Ephemeral Channels

Depleted uranium (DU) particles and DU oxides are present at military test and training ranges in the southwestern United States (U.S.) because of its use in military munitions and for armored shielding. Also, since approximately 1990, DU particles and DU oxides also occur in similar arid region military theatres throughout the world. At a study area in the northern Mojave Desert in the U.S., soil sampling and ground and aerial gamma-ray screening had suggested that DU particles and DU oxides had not migrated by surface water transport significant distances from their original location near a target area. However, no predictive models had been developed to forecast how far the particles would move with time. A flow and transport model was developed using the FLO-2D model to study the unconfined flow conditions over the complex alluvial fan topography in the study area watershed. The Zeller-Fullerton sediment transport equation was selected because of its ability to model sediment transport when a substantial portion is expected to be by bedload, an assumption warranted because of the density of DU and DU oxides (19.20 and 4.80 g/cm3, respectively). Modeling results indicate that a local 100-year storm could cause transport of both DU particles and DU oxides, primarily along well-defined channels, although transport could occur across alluvial surfaces as well. However, the transport distance of DU particles and DU oxides was limited to approximately 120 and 150 m, respectively. The modeling approach used in this study could be used as a predictive tool for transport on military testing ranges to address environmental compliance issues and protect military personnel during training exercises from potential unnecessary exposure by better delineating the eventual area where DU particles and DU oxides may occur. The predictive modeling also could be applied in military theatres where DU munitions were used to better understand the dispersal of DU particles and DU oxides over time by fluvial transport to help protect military and civilian populations from coming in contact with the high density metals.

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.

Monitoring Soil Erosion of a Burn Site in the Central Basin and Range Ecoregion: Final Report on Measurements at the Gleason Fire Site, Nevada

The increase in wildfires in arid and semi-arid parts of Nevada and elsewhere in the southwestern United States has implications for post-closure management and long-term stewardship for Soil Corrective Action Units (CAUs) on the Nevada National Security Site (NNSS) for which the Nevada Field Office of the United States Department of Energy, National Nuclear Security Administration has responsibility. For many CAUs and Corrective Action Sites, where closure-in-place alternatives are now being implemented or considered, there is a chance that these sites could burn over at some time while they still pose a risk to the environment or human health, given the long half lives of some of the radionuclide contaminants. This study was initiated to examine the effects and duration of wildfire on wind and water erodibility on sites analogous to those that exist on the NNSS. The data analyzed herein were gathered at the prescribed Gleason Fire site near Ely, Nevada, a site comparable to the northern portion of the NNSS. Quantification of wind erosion was conducted with a Portable In-Situ Wind ERosion Lab (PI-SWERL) on unburned soils, and on interspace and plant understory soils within the burned area. The PI-SWERL was used to estimate emissions of suspendible particles (particulate matter with aerodynamic diameters less than or equal to 10 micrometers) at different wind speeds. Filter samples, collected from the exhaust of the PI-SWERL during measurements, were analyzed for chemical composition. Based on nearly three years of data, the Gleason Fire site does not appear to have returned to pre burn wind erosion levels. Chemical composition data of suspendible particles are variable and show a trend toward pre-burn levels, but provide little insight into how the composition has been changing over time since the fire. Soil, runoff, and sediment data were collected from the Gleason Fire site to monitor the water erosion potential over the nearly three-year period. Soil hydrophobicity (water repellency) was noted on burned understory soils up to 12 months after the fire, as was the presence of ash on the soil surface. Soil deteriorated from a strong, definable pre-fire structure to a weakly cohesive mass (unstructured soil) immediately after the fire. Surface soil structure was evident 34 months after the fire at both burned and unburned sites, but was rare and weaker at burned sites. The amount of runoff and sediment was highly variable, but runoff occurred more frequently at burned interspace sites compared to burned understory and unburned interspace sites up to 34 months after the burn. No discernible pattern was evident on the amount of sediment transported, but the size of sediment from burned understory sites was almost double that of burned and unburned interspace soils after the fire, and decreased over the monitoring period. Curve numbers, a measure of the runoff potential, did not indicate any obvious runoff response to the fire. However, slight seasonal changes in curve numbers and runoff potential and, therefore, post-fire runoff response may be a function of fire impacts as well as the time of year that precipitation occurs. Site (interspace or understory) differences in soil properties and runoff persisted even after the fire. Vegetation data showed the presence of invasive grasses after the fire. Results from analysis of wind and water coupled with the spatial analysis of vegetation suggest that wind erosion may continue to occur due to the additional exposed soil surface (burned understory sites) until vegetation becomes re-established, and runoff may occur more frequently in interspace sites. The potential for fire-related wind erosion and water erosion may persist beyond three years in this system.

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.