1994 Conference Proceedings
Measurement and predictions of density-driven vapor flow of trichloroethylene in sandy porous media
M. Oostrom, R.J. Lenhard, C.S. Simmons, M.D. White
Pacific Northwest National Laboratory, Richland, Washington
EOS, 75(16), American Geophysical Union Spring Meeting, Baltimore, Maryland, 1994.
Abstract
Gaseous-phase advection has typically been assumed to be negligible when predicting the movement of nonaqueous phase liquid (NAPL) components in the subsurface. However, researchers have suggested that when NAPLs that have high molecular weight and high saturated vapor pressure volatilize, the mass density of the gaseous phase may become significantly greater than the ambient gaseous density. Therefore, a potential for gaseous flow may exist because of density effects, even when the total gaseous-phase pressure is constant. To investigate if density-driven advection may be significant, an experiment was conducted in a variably saturated 1-m-high by 2-m-long flow cell where trichloroethylene (TCE) volatilized from a source chamber. The temporal and spatial evolution of gaseous-phase TCE concentrations was determined by analyzing samples from a network of ports using a gas chromatograph with an electron capture detector. The sampling volume was only 25 μl to minimize disturbances to the flow field. Results have shown that at equal distances from the source chamber, TCE concentrations below the source chamber were larger than those to the left or right of the chamber. This suggests that, in addition to diffusion, density effects may contribute to the downward migration of volatile organic compounds (VOCs). The experiment was simulated with the modular engineering simulator STOMP (Subsurface Transport Over Multiple Phases). This compositional, integrated finite-difference code is currently being developed to predict the behavior of VOCs in the subsurface. When measured TCE concentrations in the source chamber and plenums are used as the boundary conditions, the numerical results compare well to the experimental results. This research was supported by the Subsurface Science Program, Office of Health and Environmental Research, U.S. Department of Energy (DOE). Pacific Northwest National Laboratory is operated for DOE by Battelle Memorial Institute under Contract DE-AC06-76RLO 1830.
An experimental and numerical study of LNAPL and DNAPL movement in the subsurface
M. Oostrom, R.J. Lenhard, M.D. White, K.R. Roberson
Pacific Northwest National Laboratory, Richland, Washington
EOS, 75(44), American Geophysical Union Fall Meeting, San Francisco, California, 1994.
Abstract
A series of multiphase experiments were conducted in a one-meter-long glass column to investigate the behavior of a LNAPL (Soltrol) and a DNAPL (carbon tetrachloride) after controlled spills in sandy porous media. In the experiments, water was drained from an initially water-saturated porous medium by gradually lowering the water table to 60 cm below the top surface. After equilibrium has been reached, a volume of either the LNAPL or DNAPL was introduced uniformly from the top boundary. NAPL and water saturations were measured frequently at several locations using a dual-energy gamma radiation system. Both NAPL and water pressures were measured at eight locations. The used NAPLs were colored with a Sudan dye, allowing visual documentation of the flow process. The experiments were simulated using the integrated finite-difference multiphase code STOMP (Subsurface Transport Over Multiple Phases).
This work was supported by the Office of Technology Development within the Department of Energy's Office of Environmental Management, under the VOCs in Arid Soils Integrated Demonstration Program. Pacific Northwest National Laboratory is operated for DOE by Battelle Memorial Institute under Contract DE-AC06-76RLO 1830.