1995 Conference Proceedings
Theory and numerical application of subsurface flow and transport for transient freezing conditions
M.D. White
Pacific Northwest National Laboratory, Richland, Washington
Proceedings of Fifteenth Annual American Geophysical Union Hydrology Days, Hydrology Days Publication, Atherton, California, pp. 339-352, 1995.
Abstract
Protective barriers are being investigated for the containment of radioactive waste within subsurface environments. Predicting the effectiveness of cryogenic barriers and near-surface barriers in temperate or arctic climates requires capabilities for numerically modeling subsurface flow and transport for freezing soil conditions. A predictive numerical model, described here, has been developed to simulate the flow and transport of radioactive solutes for three-phase (water-ice-air) systems under freezing conditions. This physically based model simulates the simultaneous flow of water, air, heat, and radioactive solutes through variably saturated and variably frozen geologic media. Expressions for ice (frozen water) and liquid water saturations as functions of temperature, interfacial pressure differences, and osmotic potential are developed from nonhysteretic versions of the Brooks-Corey and van Genuchten functions for soil moisture retention. Aqueous relative permeability functions for variably saturated and variably frozen geologic media are developed from the Mualem and Burdine theories for predicting relative permeability of unsaturated soil. Soil deformations, caused by freezing and melting transitions, are neglected. Algorithms developed for predicting ice and liquid water saturations and aqueous-phase permeabilities were incorporated into the finite-difference-based numerical simulator STOMP (Subsurface Transport Over Multiple Phases). Application of the theory is demonstrated by the solution of heat and mass transport in a horizontal cylinder of partially saturated porous media with differentially cooled ends, with the colder end held below the liquid water freezing point. This problem represents an essential capability for modeling cryogenic barriers in variably saturated geologic media.
Multiphase fluid flow in bedded porous media: 2. Numerical simulations
M.D. White, M. Oostrom
Pacific Northwest National Laboratory, Richland, Washington
M.H. Schroth, J.D. Istok, J.S. Selker
Oregon State University, Corvallis, Oregon
EOS, 76(45), American Geophysical Union Fall Meeting, San Fransico, California, 1995.
Abstract
Transient numerical simulations were conducted with the STOMP (Subsurface Transport Over Multiple Phases) code to assess the predictability of light nonaqueous-phase liquid (LNAPL) movement in the vicinity of sloping textural interfaces (capillary barriers) for variable soil water contents. The code is a three-dimensional, three-phase, compositional engineering simulator for modeling flow, contaminant migration, and remediation technologies. STOMP allows for hysteretic constitutive functions between fluid pressures, fluid contents, and relative permeabilities. Simulations were conducted using nonhysteretic van Genuchten and Brooks-Corey, as well as hysteretic van Genuchten retention functions. Simulation results were compared to results from two-dimensional chamber experiments performed in a glass chamber (50 cm x 60 cm x 0.95 cm) using Soltrol 220 as LNAPL and two grades of silica sand (12/20 and 30/40 sieve sizes) to generate fine-over-coarse sloping textural interfaces. Numerical simulator input parameters were previously determined in independent experiments. Preliminary results indicate good general agreement between model and experiments. Differences in results between hysteretic and nonhysteretic simulations as well as between simulations using different water retention functions are discussed for a range of different soil water contents. This work is funded by the Office of Technology Development within the Department of Energy's (DOE's) Office of Environmental Management, and by the Subsurface Science Program, Office of Health and Environmental Research, DOE. Pacific Northwest National Laboratory is operated by Battelle Memorial Institute for DOE under Contract DE-AC06-76RLO 1830.
Infiltration and redistribution of dense and light nonaqueous phase liquids in partly saturated sand columns.
M. Oostrom, R. J. Lenhard, M. D. White.
Pacific Northwest National Laboratory, Richland, Washington
Proceedings of Fifteenth Annual American Geophysical Union Hydrology Days, Fort Collins, CO
Abstract
Infiltration and redistribtion experiments were conducted in one-meter long columns containing uniform sands that were variably water saturated. The columns were packed with sand under saturated conditions and were subsequentially drained until the water table was 70cm below the surface. During the initial drainage, water pressures were measured at selected locations with porous cup tensiometers, and water saturations were determined using a dual-energy gamma scanner. The pressure-saturation data were used to determine van Genuchten and Brooks-Corey retention parameters. After water drainage ceased, a slug of either a DNAPL (CCl4) or a LNAPL (Soltrol®) was applied uniformly with a constant rate to the sand surface. The downward movement of the dyed NAPL was monitored visually and by determining saturations with the gamma system. Results show that both the Soltrol® and CCl4 move uniformly through the unsaturated zone. However, while Soltrol® collects in the saturated region, CCl4 'fingers' downwards through the capillary fringe and below the water table. The STOMP (Subsurface Transport Over Multiple Phases) simulator was used to numerically model the infiltration and redistribution processes. It was shown that simulations using the Brooks-Corey retention data in combination with the Burdine pore-size distribution model produced results which most nearly matched the experimental observations.