Future management options for residual inorganic solid wastes are likely to include land disposal. While the environmental ramifications of this option are now better understood, additional data is required to permit a thorough assessment of contaminant leachability from solid wastes. As part of this data gathering exercise, Environment Canada's Wastewater Technology Centre has been actively researching and developing test methods designed to measure intrinsic waste properties that affect contaminant leachability, such as metal solubilities and speciation. Based on this approach the leachability of heavy metals from sewage sludge, char and ash, municipal solid waste ashes, hazardous waste incinerator fly ashes, power plant ashes and a solidified synthetic waste were assessed.
The results indicate that incineration of sewage sludge produces a benign ash with most of the metals speciated as insoluble oxides or silicates. By contrast, incineration of municipal solid waste or hazardous wastes produces fly ashes exhibiting significant metal leachability. Environmentally sensitive metals such as Cd, Zn, Ni and Cu in these fly ashes were readily leachable and probably speciated as water soluble chloride salts. The intrinsic properties approach appears to be an effective method of assessing waste leachability.