Date of Award

1990

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

First Advisor

Stephen D. Field

Abstract

Several parameters affecting the behavior of Chromium(+VI) in deep well injection zones were studied. Temperature, pH, concentration of inorganic salt in wastewater, and organic chemicals co-injected with wastewater were considered as they affect the adsorption and reduction rates of Cr(VI). Water content, bulk density of shale and sand, and temperature were examined for their effect on the diffusion rate of Cr(VI) in porous media. Adsorption and reduction of Cr(VI) were investigated using three clays, Na-Montmorillonite, Illite, and Kaolinite, and sand from an injection well formation in southern Louisiana, and a confining layer shale obtained from a second Louisiana injection well. Diffusion rates of Cr(VI) in the confining layer shale and sand were measured using a radioactive tracer ($\sp{51}$Cr). A transport and fate model of Cr(VI) wastes was developed by incorporating the effects of reduction and adsorption in the governing equations for the injection zone sand and shale confining layers. Advection and dispersion were the driving force in the confining shale. Experimental and modeling results demonstrate that temperature and pH affected the adsorption, and reduction significantly. The amount of inorganic salt did not affect the above reactions significantly. Diffusion was affected by temperature, water content, and bulk density to a great extent. The simulation of Cr(VI) transport demonstrated the excellent capability of deep well injection zones to confine Cr(VI) wastes in that area safely without posing a threat to other groundwaters. After 500 years of continuous injection, Cr(VI) was predicted to move just a few meters vertically and less than a hundred meters horizontally at low temperature and high pH (2.0), which was the worst condition evaluated. Higher temperature and lower pH were found to reduce Cr(VI) waste transport. These results indicate that deep well injection may be used for treatment of Cr(VI) wastes with due attention paid to the favorable environmental factors such as pH, temperature, and organic compounds for the attenuation mechanisms such as adsorption and reduction, and for the retardation of Cr(VI) waste transport.

Pages

237

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