The composition (major, minor and trace elements) of approximately 400 Coolside waste samples form the Edgewater Coolside demonstration and CONSOL pilot plant tests are summarized and tabulated in this report. The composition changes in the waste samples collected during the Edgewater Coolside demonstration can be correlated with the processing variables and operation conditions. A study was conducted that focused on the formation mechanism of ettringite crystals in FGD waste materials since they were observed to form in Coolside, FBC, and AFBC derived wastes. The degree of swelling in FGD-derived waste can be correlated to the amounts of ettringite crystals present. Reactions controlling the formation, composition and disintegration of ettringite are critical in determining the overall stability and strength of cements and concretes derived from dry-flue gas desulfurization wastes. Since these wastes consist of fly ash, along with, CaSO{sub 3}, and CaSO{sub 4} and unreacted Ca(OH){sub 2}, the sulfites and sulfates react with the Ca(OH){sub 2} along with the glassy aluminosilicates in the fly ash to form calcium sulfo-aluminate minerals. Ettringite, the most important of these, is the main contributor to the compressive strength development of the FGD waste mixtures. However, excessive ettringite formation causes swelling which often leads to destructive crack formation. It has been shown that the quantity of ettringite formed and compressive strength of the FGD waste mixtures reach a maximum until ettringite begins to disintegrate. Because the formation mechanisms of ettringite are not entirely understood, swelling in FGD derived products is difficult to predict.