Mainstem Water Quality - Oil Sands Region
Athabasca River (M3, M4, M5, M6, M7 [2011-2015])
Water quality chemistry data for 17 sites in the lower Athabasca River (LAR), the Peace and Slave rivers, and their tributaries, including measurements of major ions, nutrients, metals (dissolved and total) and organics (including BTEX, cyanide and polycyclic aromatic hydrocarbons (PAHs).
Water quality sample results for major ions, nutrients, organics and total metals were assessed against 39 federal CCME 2015 and provincial ABSWQ 2014 guidelines for the protection of aquatic life. The results show that nineteen of the parameters (alkalinity, pH, 2 nitrogen nutrients, 5 total metals, methylmercury and 9 organics) showed no exceedances in any of the 1300 samples. For the remaining 20 parameters, the percentage of samples with values that exceed guideline values were: total iron, 94-98%; total aluminum, 75-78%; total copper, 36-46%; and, all other parameters, less than 20%. The high percentage of exceedances was expected as these waters are known to have naturally-occurring high concentrations of iron. For the other total metal parameters, high concentrations have been consistently observed to be associated with the high suspended sediment concentrations (410-1020 mg\/L TSS) during high flow events. Maximum values measured during these events were one to two orders of magnitude greater than the CCME guideline. Although concentrations of these total metals are above published guidelines, seasonal and annual patterns, as well as the percentage of samples with exceedances, are consistent with historical data (since the early 1990’s). Development of site specific guidelines (CCME 2003) for total metals maybe more appropriate for these waters.
Other, less frequent exceedances were also observed. Total mercury showed occasional exceedances (<6% of samples), with high values most often associated with high suspended sediment values. Total cadmium, total selenium, benzo(a)pyrene and phenol also showed occasional exceedances (1-3%) at several sites in the Peace and Slave river watersheds, but no guidelines exceedances were measured for these parameters in the lower Athabasca River. Finally, at four tributary sites, 3% of samples measured showed dissolved oxygen levels below the minimum value of the CCME guideline (6.5 mg\/L), with all of these exceedances measured under ice during low flow conditions. At these locations, similar low values have been measured in other years at these tributary sites suggesting a natural pattern of dissolved oxygen fluctuations.
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