HR: 0800h
AN: H31B-0373    [Abstracts]
TI: Significance of Diffused Zone Mass Flux Plume in Determining the Longevity of Solute Plumes Emanating From Heterogeneous DNAPL Source Zones: Intermediate-Scale Experimental Investigations
AU: * Rodriguez, D R
EM: drrodrig@mines.edu
AF: Colorado School of Mines, ESE Division, 1500 Illinois, Golden, CO 80401 United States
AU: Illangasekare, T H
EM: tissa@mines.edu
AF: Colorado School of Mines, ESE Division, 1500 Illinois, Golden, CO 80401 United States
AU: Sale, T C
EM: saletm@engr.colostate.edu
AF: Colorado State University, Dept. of Civil Engineering, Ft. Collins, CO 80523 United States
AB: Two primary mechanisms contribute to mass flux emission from source zones where DNAPLs are entrapped. The first is the result of the soluble constituents of the DNAPL dissolving into the flowing groundwater through mass transfer that occurs at DNAPL-water interfaces in residual zones and pools. The second is a result of rebounding of dissolved mass that has diffused into the low permeability zones of the aquifer during active DNAPL dissolution. The heterogeneity of the aquifer and the DNAPL entrapment architecture that determine the significance of the rebounding diffused mass contributing to source zone emission will affect the longevity of the solute plume that produces downstream risk. The goal of this research study is to develop decision tools that could be used to manage source zones where conditions dictate for the plume to persist after the DNAPL source is depleted. These decision tools are based on numerical models that simulate the fundamental processes of emission from a source zone as determined by dissolution of the entrapped sources, diffusion of mass from the source and the plume and the rebound from the low permeability zones. The results from an experimental study conducted in intermediate-scale test tanks designed to obtain an insight into this process and generate data to validate the numerical models are presented. A series of experiments were conducted in two-dimensional tanks with dimensions 4.9 m x 1.2 m x 0.06 m. The soil-packing configurations were designed in each experiment to represent different conditions where mass from dissolved plume diffuses into low permeability zones. The three conditions that were studied represented: (1) a layered system containing a high and a low permeability zones, (2) a low permeability mound embedded in a high permeability matrix and (3) an inclined low permeability layer in high permeability formation. In each case, a known volume of DNAPL was placed in the source zone and the mass depletion during dissolution was monitored using an X-ray attenuation system. The variation of mass emission as a function of time was monitored by sampling the effluent. At the end of the experiment, the low permeability zones were cored and analyzed to determine the spatial distribution of diffused mass. The experimental observations and the preliminary results of the model validation study are presented.
UR: http://cesep.mines.edu/people/rodriguez.htm
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting