Date of Award

1991

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

First Advisor

Danny D. Reible

Abstract

The transport of hazardous wastes in heterogeneous confining layers was evaluated using numerical simulations. The expected configuration of the confining layers was defined by Monte Carlo techniques assuming a binary random structure composed of pure sand and pure shale zones. Flow and solute transport in the generated configuration was determined via a finite element model. The effective permeability under saturated steady-state flow was dominated by shale permeability for higher shale fractions ($>$0.65) and by sand permeability for lower shale fraction ($<$0.4). The results agreed well with the numerical result of Desbarats (1987) and the analytical results of Dagan (1979). The effective vertical permeabilities were found to be dependent on shale size and anisotropy. Application of the techniques to a well in Jefferson Parish, Louisiana suggested that a mean advective penetration into confining layer using the injection pressure as an upper bound to the driving pressure was only 3m over 10,000 years. Transport calculations assuming a constant pressure driving force over 10,000 years suggested solute transport was controlled by hydrodynamic dispersion (dispersion + diffusion) rather than advection for higher shale fractions. Transport calculations assuming active injection for only the first 100 years suggested solute transport was controlled by diffusion for higher shale fraction. Buoyancy effects associated with salinity and temperature variations were negligible for solute transport through confining layers with a shale permeability less than 0.01 md. The results of solute transport of hazardous wastes in heterogeneous confining layers suggested that confining layers greater than 300 ft in thickness with shale fractions of greater than 0.65 and shale permeabilities of less than 0.01 md would be expected to contain injected wastes for 10,000 years.

Pages

230

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