APPLICATION OF THE QWASI FUGACITY AQUIVALENCE MODEL TO ASSESSING SOURCES AND FATE OF CONTAMINANTS IN HAMILTON HARBOR

A QWASI (Quantitative Water Air Sediment Interaction) fugacity/aquival ence mass balance model (Mackay et al. 1983, Mackay 1991, Mackay and D iamond 1989) has been developed for Hamilton Harbour to assess the sou rces and fate of contaminants in the system. Compartments defined duri ng summer months are epilimnion, hypolimnion, and surficial sediment, and during other seasons a single water column and surficial sediment layer. Processes treated are chemical emissions, advective inflows, at mospheric deposition, diffusion between air and water, and sediment an d water, sediment deposition, resuspension, and burial, transformation reactions in water and sediment, mass exchange between epilimnion and hypolimnion, and advective outflows. The model is used to describe th e fate of four chemicals, total PCBs, benzo(a)pyrene, lead, and zinc. A complete picture of the steady-state behavior of these chemicals in the harbor is deduced, and the time responses of the system inferred. The relative importance of the various sources of contaminants, includ ing sediment-water transfer, is demonstrated. It is shown that the maj or sources of contaminants are industrial emissions or wastewater trea tment plants and, secondarily, the sediments. Water column stratificat ion in summer results in minimal concentration differences in the epil imnion and hypolimnion because most of these chemicals are transferred within the water column in association with depositing particles. The short response times of the chemicals in the harbor (the water column and a 3 cm layer of active sediment) of less than 4 years suggest tha t current or recent inputs can account for most of the estimated chemi cal inventories. It is suggested that mass balance models such as this can play a useful role in remedial action planning.