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Geotechnical News • March 2018
WASTE GEOTECHNICS
mineral particles and flocculants were
released into two tributaries of the
Athabasca River (Provincial Court of
Alberta 2017). Contaminants quickly
reached the Athabasca River and were
transported downstream.
In June 2017, an Alberta court gave a
“creative sentence” to Prairie Mines &
Royalty ULC, a subsidiary of West-
moreland Coal Company, for the envi-
ronmental offence (Alberta Energy
Regulator 2017). Creative sentencing
has been one of the options used by
Alberta courts since 1993 to penal-
ize some companies found guilty of
environmental offences. The concept
is akin to restorative justice: it takes
a criminal act against the environ-
ment and uses a penalty to benefit the
environment.
Part of Prairie Mine & Royalty ULC’s
creative sentence included a fine to
fund a dam safety research project to
examine the long-term performance
of tailings dams and ponds at coal and
oil sands mines in Alberta. Currently
underway, this research is expected to
identify failure modes and degradation
rates of tailings facilities, assess how
reclaimed tailings facilities compare
to surrounding natural systems, and
assess whether these facilities pose
long-term environmental and public
safety risks. The research will classify
failure risk and recommend methods
to maintain and monitor these facili-
ties over the long term.
With many of Alberta’s coal mines
scheduled to close by 2030, and with
the closure of several oil sands tailings
ponds already initiated, this research
is timely. Its findings will increase our
understanding of tailings dam closure
and the associated risks, which may
prevent similar events in Alberta and
elsewhere.
The dam safety research project
The dam safety research project seeks
to clarify the long-term risks associ-
ated with tailings facilities so these
risks can be appropriately monitored
and managed throughout reclamation
and closure. This four-year inves-
tigation will be conducted by the
University of Alberta Department of
Civil and Environmental Engineer-
ing (DCEE) and led by Ph.D. stu-
dent Haley Schafer. The research is
complemented by an ongoing study
at DCEE led by Ph.D. candidate
Neeltje Slingerland, who is evaluat-
ing the long-term susceptibility to,
and implications of, erosion on oil
sands tailings “sand” dams, to guide
their design for post-closure stability.
Some of the investigative approaches
developed and used for this oil sands
tailings dam study are readily applied
to the broader scope of the dam safety
research project. Both studies are
overseen by Dr. Nicholas Beier and
Dr. Ward Wilson at the DCEE, who
specialize in tailings management
and design of mine waste structures,
respectively.
The project aims to answer several
questions that arise when consider-
ing the extended time frame between
when a tailings dam concludes its
active life and when it is considered a
naturally behaving landform:
• What are the failure modes, how do
they develop, and are there indica-
tors prior to failure?
• How can we monitor for adverse
conditions that lead to failure?
• How do we assess and determine
the level of risk at various times
throughout conversion?
• At what point is a tailings dam
behaving sufficiently similar to
its natural surroundings that it
becomes a landform?
• What is a reasonable return period
for maintenance and repairs? To
what extent is maintenance likely
required?
• How much financial security is
required to address these uncer-
tainties?
These questions directly impact public
safety and the magnitude of long-term
liability faced by the province. Their
answers are also essential to inform
our regulatory process and to permit
delicensing.
General objectives for the
project include
• identifying failure paths (and cor-
responding monitoring practices)
throughout the post-closure pro-
gression from a dam to a landform,
• analyzing multiple failure pathways
by quantifying the mechanism of
failure and related susceptibility to
failure over time,
• developing a risk-assessment tool
based on failure consequence,
similar to a failure modes and ef-
fects analysis (FMEA), and
• outlining an adaptive management
framework for failure modes in
post-mining tailings structures.
The investigation will include field
observation and documentation,
interviews with recognized experts
in geotechnical engineering and mine
waste design, laboratory materials
testing, regional climate analysis
for mining regions of Alberta, and
computer modelling of failure modes.
The results of the research will be
applied in an adaptive management
framework to continually improve
processes for closing tailings dams
in Alberta and for assessing failure
risks over medium to long time frames
(50 to 500 years). All findings will
be reviewed by recognized experts in
the fields of geotechnical design of
tailings dams, mine reclamation, and
regulation.
Applications of this research
As exemplified by the Obed dam
failure, geotechnical failure of a tail-
ings dam is potentially disastrous from
social, environmental, and economic
perspectives. While the AER is highly
regarded globally for its high standard
of regulation, many tailings dams
in Alberta fall under the “extreme”
failure consequence category, empha-
sizing the importance of providing
operators with clear regulations of
how to safely close and reclaim their
dams.
