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TitleCharacterization and quantification of mining-related "naphthenic acids" in groundwater near a major oil sands tailings pond
AuthorAhad, J M E; Pakdel, H; Savard, M M; Calderhead, A I; Gammon, P R; Rivera, A; Peru, K M; Headley, J V
SourceEnvironmental Science & Technology (ES & T) no. 47, 2013 p. 5023-5030,
Alt SeriesEarth Sciences Sector, Contribution Series 20120340
PublisherAmerican Chemical Society
Mediaon-line; digital
File formatpdf
NTS74D; 74E
AreaFort McMurray
Lat/Long WENS-112.0000 -111.0000 57.5000 56.5000
Subjectsfossil fuels; hydrogeology; oil sands; carbon isotopes; isotopes; tailings; tailings geochemistry; groundwater
Illustrationssktech mapstographs
ProgramCoal & Oil Resources Environmental Sustainability, Environmental Geoscience
LinksSupporting information / information supportif
AbstractThe high levels of acid extractable organics (AEOs) containing naphthenic acids (NAs) found in oil sands process-affected waters (OSPW) are a growing concern in monitoring studies of aquatic ecosystems in the Athabasca oil sands region. The complexity of these compounds has substantially hindered their accurate analysis and quantification. Using a recently developed technique which determines
the intramolecular carbon isotope signature of AEOs generated by online pyrolysis (delta-13Cpyr), natural abundance radiocarbon, and high resolution Orbitrap mass spectrometry analyses, we evaluated the sources of AEOs along a groundwater flow path from a major oil sands tailings pond to the Athabasca River. OSPW was characterized by a delta-13Cpyr value of approximately -21per mil and relatively high proportions of O2 and O2S species classes. In contrast, AEO samples located furthest down-gradient from the tailings pond and from the Athabasca River were characterized by a delta-13Cpyr value of around -29 per mil, a greater proportion of highly oxygenated and Ncontaining compound classes, and a significant component of nonfossil and, hence, non-bitumen-derived carbon. The groundwater concentrations of mining-related AEOs determined using a two end-member isotopic mass balance were between 1.6 and 9.3 mg/L lower than total AEO concentrations, implying that a less discriminating approach to quantification would have overestimated subsurface levels of OSPW. This research highlights the need for accurate characterization of "naphthenic acids" in order to quantify potential seepage from tailings ponds.
Summary(Plain Language Summary, not published)
Organic acids 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, these acids are very difficult to analyse, and traditional measurement techniques cannot distinguish between naturally occurring organic acids, and those derived from mining activities. Under the framework of the Earth Science Sector's Environmental Geosciences Program, this study is the first to accurately quantify mining-related organic acids in the groundwater near an oil sands tailings pond using a recently developed technique, in conjunction with two other established analytical approaches. This paper shows that standard methods used for environmental monitoring in the oil sands region have likely overestimated the levels of mining-related organic acids, and highlights the need for accurate characterization of organic acids to quantify potential seepage from tailings ponds.