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TitleInfluence of saline groundwater discharge on river water chemistry in the Athabasca oil sands region - a chloride stable isotope and mass balance approach
AuthorGue, A; Grasby, S E; Mayer, B
SourceApplied Geochemistry vol. 89, 2018 p. 75-85,
Alt SeriesNatural Resources Canada, Contribution Series 20170290
Mediapaper; on-line; digital
File formatpdf
AreaAthabasca oil sands region
Lat/Long WENS-112.0000 -110.0000 58.0000 56.5000
Subjectshydrogeology; Health and Safety; fossil fuels; oil sands; groundwater discharge; groundwater; groundwater circulation; groundwater geochemistry; groundwater pollution; halite; carbonate; anhydrite; total dissolved solids; spring water geochemistry; springs; chlorine geochemistry; isotopic studies; aromatic hydrocarbons; Clearwater River; Athabasca River; Devonian; Cretaceous
Illustrationslocation maps; tables; graphs; histograms; plots
ProgramGeothermal Energy, Geoscience for New Energy Supply (GNES)
AbstractA chloride mass and stable isotope (d37Cl) balance approach was employed to calculate the effect of saline groundwater discharge into the Athabasca and Clearwater rivers in the Athabasca Oil Sands Region (AOSR) in north-eastern Alberta, Canada. Saline groundwater affected by halite, carbonate, and anhydrite dissolution discharges Na-Cl type water with total dissolved solids (TDS) up to 51,700 mg/L from exposed Devonian and Cretaceous units in the river valleys in this area. In this study, nine springs of groundwater with median Cl concentration of 9800 mg/L were sampled and chloride stable isotope ratios were determined, with d37Cl values ranging from 0.2 to 1.0¿. In contrast, river waters had historical monthly median Cl concentrations between 5.9 and 49.5 mg/L and d37Cl values between -2.2 and -1.4¿. The discharge rate of saline groundwater was calculated to be 100 ± 20 L/s into the Clearwater River and 134 ± 68 L/s into the Athabasca River. The chemical composition and discharge rates of saline groundwater were used to estimate its contribution to the mass fluxes of major ions, metals, and PAHs in the Athabasca and Clearwater rivers. Overall, saline groundwater contributed less than 0.2% of river discharge, but 0.04 to 39% of major ion concentrations in the rivers, with highest contributions under winter low-flow conditions. In the Clearwater River, saline groundwater contributed 23-39% of average monthly Cl flux and 18-32% of average monthly Na flux. For the same major ion fluxes in the Athabasca River, saline groundwater contributed 12-18% and 6-12%, respectively. The influence of saline groundwater discharge on the mass flux of trace elements in the rivers was found to be negligible, contributing less than 1% of river fluxes of Cu, Ni, Pb, and Zn. Similarly, the influence on mass flux of PAHs in the rivers was found to be negligible (<0.03%) but quantifiable. These results provide important insights on the natural contributions of saline groundwater discharge to river chemistry in the AOSR, a necessary factor to consider when monitoring for anthropogenic effects of oil sands development on river water quality.
Summary(Plain Language Summary, not published)
Production of oil sands resources in northeastern Alberta has raised concerns over potential impact on the Athabasca River. Previous studies have attempted to assess this impact by simple comparison of water chemistry upstream and downstream of the oil sands area. This approach is complicated however as there is significant natural discharge of brine water to the river within the oil sands area. To account for this natural contribution to the river system a novel approach of using Chloride stable isotopes was used as a fingerprint to track the total natural contributions to the river in the area of interest.