Oils Sands Monitoring – Technical Report: Water Quality Trends in the Athabasca, Peace, and Slave Rivers from 2012-2019; Including evaluation of previous and current trend methods and influence of approaches for incorporating censored data

This report aims to update the methods for handling censored data and conducting trend analyses used in previous technical reports, and to present updated trends using new water quality data from five sites along the Athabasca, Peace, and Slave River, including two sites with previously unreported trends. It also offers recommendations for future trend analysis and water quality sampling based on statistical findings and potential monitoring objectives. Comparison of the Lower Athabasca River (LAR) site M9 with the Peace/Slave sites (EGA-LT) revealed spatial patterns in WQ trends within and outside of areas influenced by OS activities. While major ions, physicals, and nutrients exhibited largely similar trends across the three sites, suggesting region-wide drivers, M9 showed decreasing trends in both total phosphorus and particulate. More complex patterns were observed in metal concentrations. Dissolved metal trends were more comparable at M9 and M11a, while total metal trends at M12 and M11A contrasted with the consistent decreases seen at M9. Within the Athabasca, trends across the three LAR sites (M3, M7, M9) showed increasing spatial and temporal variability downstream. Flow-adjusted results indicated that M9 exhibited the greatest number of significant trends in major ions and nutrients, with nutrient concentrations generally decreasing over time. All three sites showed consistent decreases in total metal concentrations, but M7 and M9 exhibited a greater number of significant declining trends compared to M3, suggesting potential influence of downstream inputs. Additionally, significant within-site variability at M3 and M7 highlighted the importance of continued panel sampling to accurately capture local influences like tributaries and wastewater inputs. Recommendations for further statistical methods and sampling frequency of future water quality monitoring efforts are provided in the report.