2019 Base Mine Lake Monitoring and Research Summary Report: Results from 2013-2018

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Syncrude Canada Ltd.
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Syncrude's Base Mine Lake (BML) is the first, and currently the only full-scale commercial demonstration of the end pit lake technology in the oil sands industry. An oil sands end pit lake (EPL) is an area where overburden and oil sand has been removed and is then filled with fluids prior to closure. An EPL contains water (from the process of oil sands extraction or freshwater or both) and may or may not contain treated or untreated fluid tailings (FT), or other solids (for example, coarse tailings sand, or overburden).

In general, pit lakes will support ecological functions and lake specific wildlife habitat. The specific end land use goal for Base Mine Lake is that the lake will support lake ecological functions, including sustainable small-bodied fish populations (Syncrude 2016). Base  Mine Lake is expected to support conventional boreal lake functions, with water quality capable of supporting typical lake algae, plants and macroinvertebrates. Small bodied fishes will be able to survive in the lake- there will be enough biomass (food) and dissolved oxygen to  support small bodied fish populations (Syncrude 2016).

The specific objective of the BML Monitoring Program is to provide information to support the validation of Water Capped Tailings Technology (WCTT) as a viable tailings management  land reclamation option. In the early stages, the BML Monitoring Program will demonstrate that  fluid fine tailing are sequestered and that the water quality in the lake is improving. The  monitoring program is designed to do this by tracking the physical, chemical and biological  changes in BML. The program captures these changes both temporally and spatially, and  eventually in the context of regional climate cycles. The monitoring program supports regulatory compliance, but also informs adaptive management of BML.

Results so far indicate that the FFT is settling as expected by model predictions, the mudline is declining in elevation year over year, the water cap is increasing in depth, and although the turbidity in the water cap fluctuates seasonally, there is generally a decrease in the suspended solids concentration over time, especially in the upper layers of water.

Surface water quality has been improving with time in Base Mine Lake, as expected to demonstrate Water Capped Tailings Technology. The lake water is not acutely toxic. Except for F2 hydrocarbons (where the guideline value is interim and derived from soil guidelines) all parameters measured are below Alberta Surface Water Quality short term guidelines for the Protection of Aquatic Life.