AbstractDisposal of solid and hazardous wastes has become a concern in recent years. Incineration is a promising option for both, however, there are questions of public health effects and environmental acceptability of incinerator outputs. Ideally, operating conditions could be controlled to limit toxicity of residuals; to develop process models and feed‐back algorithms requires knowledge of the causal relationships between input and output to quantify induced responses.The composition of municipal solid wastes (MSW) from residential service areas was categorized and residuals from MSW incineration were examined for metal content and leachability. Sample size, sampling methodology, segregation by category and homogeneity of service area were determined to be dominant factors influencing the composition of MSW. There were notable differences in metal content of the fly and bottom ash residuals. Lead and zinc were the dominant trace metals in both ash residuals. Concentrations of cadmium and lead leached from the flyash were found to exceed EP limits. Lead and cadmium of both bottom ash and flyash fail proposed TCLP extraction limits by even larger margins. Permanent elimination of high‐temperature process ashes, classified as hazardous, must be demonstra