Geotechnical News • June 2015
25
WASTE GEOTECHNICS
18 km and may well be the largest
earth structure in the world in terms
of volume of engineered fill. In that
same address, Dr. Morgenstern also
quoted the internationally respected
water ecologist Dr. David Schindler
who declared, “If any of those tail-
ings ponds were ever to breach and
discharge into the river, the world
would forever forget about the Exxon
Valdes”.
The writers believe that the dam
safety systems for the oil sands in the
Province of Alberta are of the best
worldwide. In contrast to this opinion,
the most recent report of the Auditor
General states, “The department’s dam
safety group has no requirement to
document its work, and without such
reports, it’s hard to know if Alberta’s
dams are safe”. One could argue that
the greatest value found in any one
failure is that it rivets attention and
forces us to examine and re-evaluate
all of our structures and systems.
The report
The report on the Mount Polley Tail-
ings Storage Facility Breach issued
by the IEEIRP is comprehensive. The
principal finding was that the breach
within the perimeter embankment
occurred as a result of a foundation
failure in a glaciolacustrine layer
referred to as the Upper GLU. The full
panel report can be found at
https://
-
report.
We encourage our readers to
download and examine the full content
of the report.
We cannot discuss the details of the
panel report nor all of its discussions,
recommendations and conclusions in
this brief article. However, one of the
most significant statements is centered
on the historical record of active tail-
ings dams in the province of British
Columbia during the 46 years since
1969, and the seven failures that have
occurred during this period. Statisti-
cal evaluation of the historical record
finds a failure frequency of 1.7×10
-3
per dam per year or approximately a
one in six hundred chance of a tailings
dam failure in any particular year. In
other words, without improved per-
formance, the province can expect (on
average) that there will be two failures
every 10 years. Based on this analysis,
“the panel firmly rejects any notion
that business as usual can continue”.
With respect to risk-based dam safety
practice, “the panel does not accept
the concept of a tolerable failure
rate for tailing dams”. This assertion
resulted in the panel recommending
the implementation of the best avail-
able tailings technology (BAT) based
on the BAT principles that are outlined
as follows:
1. Eliminate surface water from the
impoundment.
2. Promote unsaturated conditions in
the tailings with drainage provi-
sions.
3. Achieve dilatant conditions
throughout the tailings deposit by
compaction.
While the panel recognized the issue
of chemical stability associated with
the elimination of water from the
tailings deposits, the BAT principles
stand as a strong recommendation for
the future of tailings management.
Implementation of the BAT principles
for the surface storage of tailings can
lead to the use of filtered tailings tech-
nology. Filtered tailings technology,
often called “dry stack tailings”, when
properly designed and formed can
satisfy each of the BAT components.
The panel points to the Greens Creek
mine in Alaska as an example where
“dry stack tailings” have been suc-
cessfully constructed in a wet climate
that is similar to many sites in British
Columbia.
Implications
The first point we would like to
remind our readers is that the report
on the Mount Polley Tailings Storage
Facility Breach and its recommenda-
tions were written for the Govern-
ment of British Columbia and outline
actions to ensure that similar failures
do not occur at other mine sites in the
province. For clarity, it is important to
point out that the mandate given to the
panel was for the ‘Safety Case’ and
not the environmental issues related
to chemical stability. Thus the panel
points out “water covers run counter
to the BAT principles” and that “the
Greens Creek filtered tailings stack showing trucked tailings placement and
trafficability.
