Abstracts

The open pit mining of coal results in the formation of new landforms constructed from
waste rock. Rock drains, either constructed or formed during dumping by natural segregation,
underlie some of these landforms. Constructed rock drains are often designed to convey
surface water from higher in the watershed through the waste rock dumps. Rock drains also
collect water moving through the waste rock and convey it to adjacent surface and ground
water. Long-term monitoring of the chemistry of water conveyed by rock drains provides
an opportunity to characterize the rates of flushing of these constituents through the waste
rock piles. In this study, a conceptual model for the long-term release of nitrate (NO 3
), selenium
(Se), and sulfate (SO 4
) from coal waste rock piles is developed and used to interpret
monitoring data from eleven rock drains of varying ages in the Elk Valley, British Columbia.
The hypothesis of the conceptual model is that the flushing of the first pore volume of water
within the waste rock can be characterized by NO 3
release. The NO 3
is derived from blasting
and is considered to be a conservative species. The first pore volume will also contain SO 4
and
Se generated by oxidation of waste rock during blasting and pile construction. Post-depositional
oxidation and production of SO 4
and Se are identified by the evolution of the effluent
signature from an initial SO 4
/NO 3
ratio, representative of the initial pore fluid at deposition,
to an increasing SO 4
/NO 3
ratio as the initial pore volume is released and Se and SO 4
are
produced by oxidation. This hypothesis is tested by interpreting the patterns of NO 3
, SO 4
,
and Se release as described by SO 4
/ NO 3
and Se/SO 4
ratios. In cases where upstream sources
are contributing to the observed flow and concentrations within the rock drain, an attempt
is made to correct the monitoring data so that it represents only the contribution from the
waste rock overlying the rock drain. The concentrations of NO 3
and SO 4
were found to
correspond to differences in the chronology of waste rock placement, while the Se/SO 4
ratios
were relatively constant and consistent with ratios associated with oxidation. A model of the
evolution of the effluent chemistry was developed using a system dynamics model comprised
of stocks (water storage) and flows (flushing) within blocks of waste rock placed at various
times within a watershed. The model illustrates how stored water volumes, rates of flushing,
production rates, dump chronology, and, where applicable, upstream sources control the
evolution of rock drain chemistry over time. The goal of this work is to develop methods of
evaluating the impact that various dump designs might have on the timing and magnitude
of NO 3
, Se, and SO 4
releases.
110 - Characterisation of physical mass transport through oil
sands fluid fine tailings in an end pit lake: a multi-tracer study
Kathryn Dompierre & Lee Barbour
Department of Civil and Geological Engineering - University of Saskatchewan, Saskatoon,
Saskatchewan, Canada
The first end pit lake in the Athabasca oil sands region has been developed by Syncrude
Canada Ltd. as part of their closure design for the Mildred Lake Mine site, 40 km north of
Fort McMurray. The end pit lake, referred to as Base Mine Lake, was constructed within a
mined-out pit, and incorporates 186 Mm 3 of fluid fine tailings (FFT) below an 8 m water
cap. Fluid fine tailings are a dense fluid with dispersed, suspended solids, residual bitumen
and elevated TDS (Siddique et al., 2007). Chemical constituents of concern may move
IAH-CNC 2015 WATERLOO CONFERENCE
119