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TitleDistinguishing natural from anthropogenic sources of acid extractable organics in groundwater near oil sands tailings ponds
AuthorAhad, J M EORCID logo; Pakdel, H; Gammon, P R; Mayer, B; Savard, M MORCID logo; Peru, K M; Headley, J V
SourceEnvironmental Science & Technology (ES & T) 2020 p. A-J, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20190306
PublisherAmerican Chemical Society
Mediapaper; on-line; digital
File formatpdf; html
NTS74E/03; 74E/04; 74E/05; 74E/06
AreaMuskeg River; Fort McMurray; Athabasca River
Lat/Long WENS-111.6667 -111.2333 57.4167 57.1167
Subjectsenvironmental geology; hydrogeology; fossil fuels; geochemistry; Nature and Environment; Economics and Industry; Science and Technology; petroleum industry; hydrocarbon recovery; oil sands; waste disposal sites; tailings; tailings geochemistry; groundwater resources; groundwater geochemistry; groundwater pollution; groundwater flow; mass spectrometer analysis; pyrolysis; isotopic studies; sulphur isotope ratios; carbon isotopes; sulphur geochemistry; radioisotopes; bedrock geology; lithology; sedimentary rocks; bitumen; models; statistical analyses; observation wells; watersheds; Athabasca Oil Sands; McMurray Formation; Muskeg River Watershed; mining industry; oil sands process-affected water; natural sources; anthropogenic sources; naphthenic acids; methodology; acid extractable organics; carbon-14
Illustrationsphotographs; flow diagrams; plots; bar graphs; satellite images
ProgramEnvironmental Geoscience, Sources
Released2020 01 29
AbstractDistinguishing between naphthenic acids (NAs) associated with oil sands process-affected water (OSPW) and those found naturally in groundwaters in contact with the bituminous McMurray Formation poses a considerable analytical challenge to environmental research in Canada's oil sands region. Previous work addressing this problem combined high-resolution Orbitrap mass spectrometry with carbon isotope values generated by online pyrolysis (delta-13Cpyr) to characterize and quantify the acid extractable organics (AEOs) fraction containing NAs in the subsurface near an oil sands tailings pond. Here, we build upon this work through further development and application of these techniques at two different study sites near two different tailings ponds, in conjunction with the use of an additional isotopic tool-sulfur isotope analysis (delta-34S) of AEOs. The combined use of both delta-13Cpyr and delta-34S allowed for discrimination of AEOs into the three endmembers relevant to ascertaining the NA environmental footprint within the region: (1) OSPW; (2) McMurray Formation groundwater (i.e., naturally occurring bitumen), and; (3) naturally occurring non-bitumen. A Bayesian isotopic mixing model was used to determine the relative proportions of these three sources in groundwater at both study sites. Although background levels of OSPW-derived AEOs were generally low, one sample containing 49-99% (95% credibility interval) OSPW-derived AEOs was detected within an inferred preferential flow-path, highlighting the potential for this technique to track tailings pond seepage.
Summary(Plain Language Summary, not published)
Naphthenic acids (NAs) occur naturally in bitumen and become concentrated in waters used in oil sands mining operations. The potential for these acids to contaminate groundwater and aquatic ecosystems is a major focus of environmental monitoring studies in the Athabasca oil sands region (Alberta, Canada). However, current methods are unable to distinguish naturally occurring from mining-related NAs. In this study, we demonstrate the effectiveness of a novel dual isotope technique that is able to do this. With the help of an isotopic mixing model, we quantified the proportions of mining-related and naturally occurring NAs in groundwater near two oil sands tailings ponds. Low levels of mining-related NAs were found in groundwater at both study sites.

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