HR: 09:30h
AN: H21H-07 INVITED     [Abstracts]
TI: Up-scaling of Mass Transfer From Entrapped DNAPL Sources From Laboratory to Field- Experimental Validation of an Empirical Approach
AU: * Illangasekare, T H
EM: tissa@mines.edu
AF: Center of Experimental Study of Subsurface Environmental Processes (CESEP), ESE, Colorado School of Mines 1600 Illinois St, Golden, CO 80401-1887 United States
AU: Saenton, S
EM: ssaenton@mines.edu
AF: Center of Experimental Study of Subsurface Environmental Processes (CESEP), ESE, Colorado School of Mines 1600 Illinois St, Golden, CO 80401-1887 United States
AB: Mass transfer from entrapped dense non-aqueous phase liquids (DNAPLs) in the source zones of aquifers takes place in three-dimensional ground water flow fields under conditions of natural soil heterogeneity and complex entrapment architecture. However, it is only possible to characterize the mass transfer process in the laboratory in soil columns under one-dimensional flow with homogeneous soils and residual entrapment. Phenomologically based empirical correlations (Gilland-Sherwood models) based on these experiments expected to fail in attempting to predict the dissolution of entrapped DNAPLs in the field, as they do not capture the effects of heterogeneity and DNAPL entrapment architecture with both residual zones and pools. Numerical simulation of DNAPL dissolution at field scale requires the discretization of the problem domain into grid blocks and assignment of an effective mass transfer coefficient to each of these blocks containing DNAPL. A methodology of up-scaling is needed to determine the grid-scale effective mass transfer coefficient from the laboratory determined empirical correlations. Key features of an empirical method for up-scaling the mass transfer coefficients from the laboratory to the field is presented. In this method development, we hypothesized that up-scaled effective mass transfer coefficients need to contain information on the field-scale heterogeneity and spatial distribution of DNAPL mass. This hypothesis was tested through a Monte Carlo based numerical experiment. The methodology involves the use of set of parameters that captures the heterogeneity of the aquifer and the DNAPL entrapment architecture. These parameters were determined to be the variance of logarithm of hydraulic conductivity, correlation lengths, and the second moments of DNAPL mass distribution. Monte Carlo numerical simulation experiments combined with an inverse modeling were conducted to determine the empirical parameters in the up-scaled Gilland-Sherwood mass transfer correlation. Through these numerical modeling studies, the up-scalable mass transfer correlation was successfully developed and verified. Sensitivity analyses indicate that the normalized second moment that described the spreading of DNAPL mass in the vertical directions was the most sensitive parameter in the up-scaled mass transfer coefficient. The methodology was validated using dissolution data generated in intermediate scale soil tanks where the DNAPL was placed in a source zone to create complex entrapment architecture.
DE: 1828 Groundwater hydraulics
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
DE: 1847 Modeling
SC: Hydrology [H]
MN: Fall Meeting 2005