A 300 m deep monitoring well was completed to the Detroit River Group of formations in Sarnia, Ontario, to evaluate the potential near-surface impacts resulting from previous deep injection of industrial waste. Detailed logging, testing, and sampling were performed to evaluate the vertical distribution of industrial waste and to determine hydraulic conductivity and hydraulic head in the disposal horizon and in the confining formations. Results of hydraulic testing indicate the hydraulic conductivity of the disposal formation is 2 × 10−9to 2 × 10−7 m/s and that of most of the confining shale and limestone formations is less than 1 × 10−10 m/s. Analyses of groundwater samples and results from other studies show that industrial waste, characterized by elevated phenol concentrations, is present in a 10 m horizon in the Lucas dolomite disposal formation at 192 m depth. Waste is also likely present within 2–3 m thick, high-permeability limestone layers at 74 and 123 m depth in the confining units of the Hamilton Group. Because of the generally low vertical hydraulic conductivity of the confining formations, waste in the permeable limestone layers was likely introduced via poorly constructed disposal wells, cavern storage wells, or abandoned oil and gas wells. The hydraulic conductivity and hydraulic head data indicate the high pressures resulting from injection into the disposal formation have dissipated. The head within the zone of residual contamination in the disposal formation is now 8 m below the level of the St. Clair River. The hydraulic data and chemical composition of the injected waste show that the discharges of tarry liquids on the bottom of the St. Clair River in 1984 and 1985 were not caused by upward migration of injected waste.Key words: deep-well disposal, pressurized waste injection, industrial waste, Sarnia.