A Study of the Chemical and Physical Properties of Syncrude's Tailings Pond, Mildred Lake, 1980

Resource Type
Authors
Mike MacKinnon
Resource Date:
1981
Page Length
126

Selected chemical and physical properties of the tailings pond were examined in 1980. The distributions of specific variables with depth and season within the tailings pond were determined (temperature, pH, conductivity, suspended particulate matter, total solids, bitumen, major anions, major cations, organic carbon, nutrients, phenols, and trace metals). From the resulting information, a generalized picture of the present state of the tailings pond was obtained. In 1980, the tailings pond was a highly stratified waterbody with a low density, well mixed surface zone (0-6 m) overlying a high density deep water zone (>10 m) where mixing is slow. Between these two zones, lies a zone of rapidly changing values in which a thermocline (zone of rapid temperature change) and a pycnocline (zone of rapidly increasing density) are established. The exact depth at which these changes begin varies with season (shallowest in spring and early summer, deepening during summer and fall). In the surface zone (0-6 m), most concentrations were generally low and uniform, while in the deep zone (>10m), the concentrations of variables, particularly those associated with the particulate fraction (fines, bitumen), were high. In the deepest waters (>15m), a sludge zone of high fines (>4%) and high bitumen (>5000 mg L-1) concentration was evident. Throughout this tailings pond study, the concentrations of most dissolved variables (nutrients, trace metals, phenols, organic carbon) were generally higher than in surrounding waters. While the concentrations are high, I would not consider the levels to be high enough to be considered excessive, at present. The quality of the tailings pond waters during the 1980 study was acceptable for maintenance of maximum rate of recycle of water from the tailings pond for plant processes. The tailings pond is an environmental hazard both physically and chemically. The tailings waters are acutely toxic (LC50<4% for rainbow trout by 96 hour static bioassay). However, the quality of these waste waters in the tailings pond at this stage of its development has not deteriorated to a level where it cannot be reclaimed.