Bitumen exploitation in Alberta’s oil sand region generates considerable amounts
of waste including tailings and process-affected water that needs reclamation. Water
capped tailings technology (WCTT) is currently being assessed as a potential wet
reclamation strategy in the oil sand by the commission of Base Mine Lake (BML), the first
commercial scale Pit Lake. Pit Lakes consist of ~40m of fluid fine tailings (FFT) deposited
in old mine pit covered with a ~10m water cap. In order to be successful, pit lakes much
achieve the ecological roles of a natural lake, which includes colonization of the water by
macrofauna therefore necessitating the water cap to be oxic. Due to the reductive nature of
the tailings, oxygen consuming constituents (OCC) such as methane, sulfide and ammonia
are released from the FFT into the water cap potentially posing a threat to the success of
the reclamation. Additional seasonal effects such as stratification and ice cover may further
affect oxygen consumption by isolating parts of the water cap therefore allowing
accumulation of OCC. Results shows that BML thermally stratifies during the summer and
winter and that oxygen persist throughout the water cap despite reaching low level at the
FFT-water interface (FWI) during summer. Consistent with the FFT acting as an OCC
source, aqueous CH 4 and NH 4+ concentrations were highest closer to the FWI, decreasing
upwards into the water cap. Using linear regression CH 4 was shown to be an important
OCC during the summer of 2015 while NH 4+ and CH 4 were both important for the summer
of 2016 highlighting the emergence of nitrification in BML. Detailed analysis of seasonal
data revealed that accumulation of OCC below the hypolimnion depletes oxygen and favors
methanotrophic activity. Results from both studies suggest that methanotrophs have a
competitive advantage at low oxygen levels against nitrifiers. / Thesis / Master of Science (MSc) / Bitumen extraction in Alberta’s oil sand region generates substantial amounts of
waste including tailings that needs reclamation. Pit Lakes have been proposed as a
reclamation strategy, where tailings are deposited into a mined-out pit and covered with a
water cap. To achieve the reclamation goal, the lake must be able to sustain life and must
therefore maintain an oxic water cap. The underlying tailings poses a threat to the
oxygenation of the lake because of the constant release of compounds that have the
potential to consume oxygen. Additional seasonal effects due to temperature change may
further affect oxygen consumption by isolating parts of the water cap. In this thesis the
results of two years of field sampling and analyses show that despite active oxygen
consumption from tailings-released compounds, oxic status is achieved in the upper layer
of the lake during summer and under ice.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/22274 |
| Date | January 2017 |
| Creators | Risacher, Florent Frédéric |
| Contributors | Warren, Lesley A, Earth and Environmental Sciences |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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