Much of urbanized North America is experiencing major problems with regard to the management of municipal waste; production exceeds the capacity of management systems to handle waste by reuse, recycling, incineration and landfilling. The last is a multi-billion dollar a year industry and involves a large research effort by various public and private agencies to minimize environmental degradation from leachate contamination of groundwaters. This paper presents the preliminary results of a long-term study aimed at establishing the regional. Quaternary glacial geology of existing and projected landfills in southern Ontario, and the groundwater contamination potential of such landfills. It can be shown that at least 300 landfills in southern Ontario are located in abandoned aggregate or bedrock quarries where little regard was given to ground water contamination. Many landfills contain toxic liquid and solid industrial wastes, but few data are available. Areas of fine-grained, impermeable glacial sediments, affording some degree of natural protection, have are stricted extent in southern Ontario; silt- and sand-rich tills predominate and, despite their massive, dense character, have significant bulk permeabilities. Projected sites can be fully engineered and protected by "hydraulic traps", thereby minimizing groundwater impacts, but the presence of nearly 1200 sites that lack any engineering poses a significant threat to groundwater supplies. Groundwater flow paths and estimates of groundwater discharge to Lakes Erie and Ontario are very poorly understood; a pressing research need is to determine the effects of climate warming and lowering of the groundwater table on subsurface contaminant transport to the Great Lake basins through complex glacial stratigraphies.