Date of Award

1999

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

First Advisor

Donald Dean Adrian

Abstract

Column leaching tests were conducted on two freshwater sediments and two estuarine sediments. Leachate samples were analyzed for total organic carbon (TOC), cadmium, chromium, copper, iron, manganese, lead, nickel, and zinc. Metal and TOC elution curves for freshwater sediments were fundamentally different from estuarine sediment elution curves. The difference was due to colloid-facilitated transport of metals and TOC in estuarine sediments that was caused by salt washout during leaching with distilled-deionized water. Metals and TOC concentrations in freshwater sediment leachates tended to monotonically decrease from initial pore water concentrations. Leaching of metals and TOC from freshwater sediments was modeled with a retardation model and a retardation model that included diffusion from immobile water regions. Comparison of modeled and measured metals concentrations showed that long-term metals leaching from freshwater sediments was governed by diffusion from immobile water regions. Equilibrium-controlled desorption of metals from freshwater sediments was minimal except for manganese. TOC leaching, however, was described by equilibrium-controlled desorption. Estuarine sediments showed a complicated elution history involving an increase in metal and TOC concentrations in leachate following washout of the sediment salt. This phenomenon qualitatively agreed with the Gouy-Chapman double-layer model for the functional dependence of spacing between charged plates on ionic strength. The elution of salt reduced ionic strength and increased the double-layer thickness between sediment colloids. As the double-layer thickness increased, the tendency for colloids and the contaminants bound to colloids to become entrained in flow during column leaching increased. A leaching model based on Gouy-Chapman theory for the effects of salt washout on contaminant leachate concentrations simulated the elution curves for one estuarine sediment but was less effective in simulating the elution curves for the other estuarine sediment.

ISBN

9780599372610

Pages

278

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