GEOTECHNICAL PROPERTIES AND LANDFILL DISPOSAL OF FGD SLUDGE.

Extensive test data from more than a decade of research are compiled on the geotechnical engineering properties of flue gas desulfurization (FGD) sludges with emphasis on double alkali sludges and sludge-additive (primarily fly ash) mixtures, and these data, tempered with field experiences, are utilized to assess the feasibility and difficulty of landfill disposal. Most FGD sludges are silt-like materials composed primarily of calcium sulfite and calcium sulfate. In general, as-produced sludges can not be effectively compacted due to their high water content, and, if landfilled, they must be dewatered or blended with a dry additive to bring the resulting water content closer to its optimum value. For commonly encountered initial shear strengths of the sludge, slopes on the order of 20 degree with heights of 20 to 30 feet can be constructed. The passage of time serves to enhance the strength and stability of FGD sludges due to consolidation and the development of chemical bonds, and slopes of 45 degree to 60 degree with heights of 20 or 25 feet will be stable in material a few years old.