34 research outputs found
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Surface water and erosion calculations to support the MDA G performance assessment
The performance of MDA G is dependent on surface hydrological and ecological processes because radionuclide transport by surface runoff can affect human and/or environmental receptors directly and the percolation for the subsurface radionuclide transport pathway is determined by the water balance in the near surface. For subsurface disposal of waste, surface soil erosion reduces the effectiveness of the surface cover and if wastes are exposed, then surface runoff can transport contaminants either in a soluble phase or sorbed to eroded soil particles. The objectives of this section are to estimate the effects at MDA G of surface runoff, soil erosion, and percolation. The conceptual and mathematical models will be reviewed, parameter estimation for the models will be presented and results and sensitivity analyses for a surface cover at MDA G will be presented
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The effects of spatially-varying soil properties on soil erosion
The objective of this study is to investigate the effects of only rainfall excess generation on erosion. We illustrate the effects of spatial variation in saturated hydraulic conductivity (K/sub s/) on the spatial and temporal distributions of erosion resulting from overland flow. We use this as a basis to demonstrate the potential for bias in parameters estimated from field data. Mathematical modeling of soil erosion must include surface runoff the dominant transport mechanism. Rainfall excess when routed over the surface, produces a distribution of velocities and depths in response to surface, roughness, surface form or microtopography, and available water. The spatial distribution of velocities and depths strongly affects sediment delivery as well as the re-distribution of soil on the hillslope. 23 refs., 12 figs., 3 tabs
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Modeling study of solute transport in the unsaturated zone: Workshop proceedings
Issues addressed were the adequacy of the data for the various models, effectiveness of the models to represent the data, particular information provided by the models, the role of caisson experiments in providing fundamental knowledge of porous-media water flow and solute transport, and the importance of geochemistry to the transport of nonconservative tracers. These proceedings include the presentations made by each of the modelers; the summary document written by the panel; and a transcript of the discussions, both the discussions that followed individual presentations and the general discussion held on the second day. This publication completes the series on the workshop. Volume I in the series (NUREG/CR-4615, Vol. I) contains background information and the data sets provided each modeler
Filament Winding Technology: A Numerical Simulation And Experimental Validation of the Winding And Curing Phases
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Effects from influent boundary conditions on tracer migration and spatial variability features in intermediate-scale experiments
In previous unsaturated transport studies at Los Alamos dispersion coefficients were estimated to be higher close to the tracer source than at greater distances from the source. Injection of tracers through discrete influent outlets could have accounted for those higher dispersions. Also, a lack of conservation of mass of the tracers was observed and suspected to be due to spatial variability in transport. In the present study experiments were performed under uniform influent (ponded) conditions in which breakthrough of tracers was monitored at four locations at each of four depths. All other conditions were similar to those of the unsaturated transport experiments. A comparison of results from these two sets of experiments indicates differences in the parameter estimates. Estimates were made for the dispersion coefficient and the retardation factor by the one-dimensional steady flow computer code, CFITIM. Estimates were also made for mass and for velocity and the dispersion coefficient by the method of moments. The dispersion coefficient decreased with depth under discrete influent application and increased with depth under ponded influent application. Retardation was predicted better under the discrete influent application than under ponded influent application. Differences in breakthroughs and in estimated parameters among locations at the same depth were observed under ponded influent application. Those differences indicate that there is a lack of conservation of mass as well as significant spatial variability across the experimental domain. 14 refs., 9 figs., 8 tabs
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Integrated systems analysis applied to environmental remediation
At the request of the Congressional Task Force on the Salton Sea and the Salton Sea Authority, the authors examined various technologies that have been proposed to reduce the decline in the Salton Sea. The primary focus of the technologies was to reduce the salinity of the Salton Sea, with secondary objectives of maintaining the present shoreline and to have a minimum cost. The authors found that two technologies, pump-out and diking, could provide the required salinity reduction. The pump-out option would result in a smaller Sea while to diking option would create a high salinity impoundment area in the Sea. The costs for the two options were similar. Desalination and pump-in; pump-out options were rejected because of high costs and because they did not provide a sufficient reduction in the salinity of the Salton Sea. The end product of the project was testimony before the Subcommittee on Water and Power, U.S. House of Representatives Committee on Resources, given October 3, 1997
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Computerized tomographic analysis of fluid flow in fractured tuff
The purpose of this summary is to demonstrate the usefulness of X-ray computerized tomography to observe fluid flow down a fracture and rock matrix imbibition in a sample of Bandelier tuff. This was accomplished by using a tuff sample 152.4 mm long and 50.8 mm in diameter. A longitudinal fracture was created by cutting the core with a wire saw. The fractured piece was then coupled to its adjacent section to that the fracture was not expected. Water was injected into a dry sample at five flow rates and CT scanning performed at set intervals during the flow. Cross sectional images and longitudinal reconstructions were built and saturation profiles calculated for the sample at each time interval at each flow rate. The results showed that for the test conditions, the fracture was not a primary pathway of fluid flow down the sample. At a slow fluid injection rate into the dry sample, the fluid was imbibed into the rock uniformly down the length of the core. With increasing injection rates, the flow remained uniform over the core cross section through complete saturation
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Analysis of caisson transport experiments by travel time approach
The transport experiments conducted by Los Alamos National Laboratory in an intermediate-scale caisson are described. The results suggest that the solute spreading pattern has been dominated by the effect of spatial variability of hydraulic properties. A stochastic model of horizontally varying velocity distribution is employed in order to interpret the concentration data in terms of travel time distribution. A satisfactory match between the measured solute mass cross-sectional transfer in saturated flow and model is achieved for a standard deviation of the logconductivity of 1.2. The model may serve for interpretation of transport in unsaturated flow and for reactive solutes. 14 refs., 7 figs