Date of Award

12-2002

Type

Thesis

Major

Earth and Space Science - Environmental Science Track

Department

Earth & Space Science

First Advisor

William Frazier

Abstract

Surface impoundments are used extensively throughout the utility industry to store the combustion byproducts, or ash, from coal-fired generating facilities. Following combustion, the metals, naturally contained within coal at low concentrations, may become highly concentrated within the ash. These combustion byproducts are then piped out in a water-ash slurry to the surface impoundments where the ash weathers to- a clay- like substance after approximately 10 years. It is feared that these metals that are contained within the ash could possibly leach into the ground and contaminate the local groundwater. Utilizing a open column percolation test to determine the hydraulic conductivity of the ash, a set of tests were run to see what metals were contained within the test leachate using permitted discharge from the generating facility (Georgia Power Company's (GPC) Plant McDonough, Smyrna, Georgia). The permitted discharge is a slightly alkaline fluid, with a pH range of 7.08-8.03. Toxicity Characteristic Leaching Procedure (TCLP) was then conducted to see what metals would leach from the ash in an acidic (pH range of 4.93 +/- 0.05) environment. The results were then compared to provide a best and worst case scenario for metals leaching from the ash pond into groundwater supplies. The relatively low levels of metals contained in the leachate from the TCLP tests suggest that after a surface impoundment is no longer utilized, the acidic nature of rainwater would not cause metals to leach into groundwater supplies. Calcium, an important nutrient for plants, was shown in the TCLP tests to be the one metal consistently available from the ash in an acidic environment. This might be the reason cattails {Typha spp.) and pines (Pinus spp.) are so numerous within the ash pond's older areas. This large abundance of leachable calcium is due to the large percentage of ash comprised of calcium oxide (CaO), which has a relatively high solubility. The coal combustion byproducts (CCBs) are commingled within the pond so utilization for beneficial purposes such as concrete aggregate, Portland cement substitute, asphalt shingles, etc. would require separating the CCBs into their components (fly ash, bottom ash, boiler slag, and flue gas desulfurization (FGD) material). It is recommended that an economic feasibility study be conducted on the ash pond(s) at GPC's Plant Arkwright, a plant that is to cease operations in the near future, to see if it is economically feasible to separate the CCBs in such a way that other industries could use them.

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