The report summarizes progress on a project to determine the range of variability of the solids from scrubbers at the Shawnee Test Facility, and to attempt to correlate this variability with plant operating conditions. Slurry and solids characterization studies were conducted on 84 samples from the TCA and venturi-spray tower. The solids samples generally consisted of calcium sulfite hemihydrate (50-70%) and fly ash (20-40%) with trace quantities of gypsum, unreacted absorbent, and quartz. The form of the sulfite crystals was directly related to the absorbent used (lime or limestone), but independent of the scrubber type (TCA or venturi-spray tower). With limestone, the sulfite crystallized as well-formed single plates; with lime, it appeared as spherical, closely interpenetrating aggregates. The average size of the sulfite plates from the limestone system was inversely related to system stoichiometry; the lime system had no such relationship. The fly ash in the samples consisted of solid or hollow spheres of amorphous aluminosilicate material (sometimes containing calcium and/or iron). Slurry sedimentation behaved in three basic modes: clarification, zone settling, and compression settling. Solids morphology exerted a strong influence on settling behavior. For samples with large proportions of very small plates or complex crystalline forms, settling was inhibited.