Geotechnical News • June 2016
39
WASTE GEOTECHNICS
categories had been included on their
sites, and if so, over what time frame
it had been a goal and if they had been
ultimately successful in achieving the
goal.
From the feedback received, we could
identify whether each goal was (1)
regularly or rarely set for their sites,
(2) evolving or devolving in use over
time, and (3) to what degree the goal
was successfully achieved in a global
context. Answers were recorded in
terms of respondents’ overall experi-
ences throughout their cumulative
work histories and specific sites were
not listed.
Survey outcomes
A major focus of the survey was
the surface integrity of mined land.
As such, topography, above-grade
landforms such as tailings facilities or
waste rock dumps, and surface stabil-
ity were emphasized.
Below is a summary of the more
thought-provoking survey results:
Goal
: Elimination of erosion by wind
or water
A strong track record of
successful closure and
reclamation works is
required to more easily
achieve public license for
future mining projects
Goal frequency
: 97%
Success rate
: 54.5%.
Erosion control has been a longstand-
ing (20+ years) goal, so one must
question why it is only successfully
achieved about half of the time.
Depending on geographic location and
associated climate, erosion occurs to
varying degrees due to the action of
wind and/or water over land surfaces.
Erosion can be a significant problem
where highly erodible sands and silts
comprise surface layers of the con-
structed soil profile. These materials
provide good infiltration during minor
storm events, but during heavier storm
events dramatic rills can form. When
not promptly patched these rills can
rapidly become gullies that inhibit
vegetation growth, remove existing
vegetation, and require heavy equip-
ment to repair. If left unrepaired, water
quality can be negatively affected to
varying degrees depending on the tail-
ings exposed: increased sediment load,
development of acid rock drainage
(ARD), mobilization of heavy metals
and/or failure of mining structures are
a few possible results (Nicolao, 2003).
Goal:
Prevention of contamination of
off-site land or water
Goal frequency
: 98%
Success rate:
42%
Mining voids, waste rock piles, and
mine tailings can result in the con-
tamination of off-site areas through
a number of pathways: excess sedi-
ment transport, and the mobilization
of ARD, heavy metals, and neutral
drainage through water pathways for
example, to name a few.
There are various approaches to
managing these contamination sources
- much of which is mobilized by wind
and water. In some cases, generation
of contamination can be hindered or
treated entirely prior to closure, and
this means that ongoing water treat-
ment is not necessary. In other cases,
vegetated wind screens can be planted
prior to mining to reduce wind-blown
transfer. Many of these solutions
require site inventories prior to the
start of mine operations.
Goal:
No ongoing water treatment
required in perpetuity
Goal frequency:
84%
Success rate:
32%
Although not directly surveyed, this
makes one wonder if the remaining
16% of respondents’ who did not
include this as a goal had accepted the
fact that post-closure water treatment
would be required in perpetuity, and
that those companies had acknowl-
edged their liability and maintenance
costs would be infinitely ongoing. The
same can be said for the next goal.
Goal:
No tailings ponds/wet covers on
site in perpetuity
Goal frequency:
55%
Success rate:
34%
In light of several recent large tailings
dam failures, there has been a marked
move towards dry stack tailings and
other options such as co-mixing that
are not associated with catastrophic
failures. This trend is expected to
continue as public awareness and mine
size increase.
Goal:
Create a geomorphic/ natural-
ized (versus uniform/ platform-bank)
closure topography
Goal frequency:
94% (78%)
Success rate:
44% (53%)
In terms of topography, survey results
showed that there is a marked trend
towards the creation of more natural-
ized topographic landforms, and away
from the more traditional construction
of uniform slopes and platform-bank
topography. This movement began in
the early 2000’s with work by J.M.
Nicolao in Spain, Terrence J. Toy
in the USA, and Les Sawatsky in
Canada.
Naturalized or geomorphic approaches
to man-made topography involve the
creation of natural analogues through
landforming for closure. The aim of
this approach is to reduce erosion
and sediment transport, and to reduce
the intensity of water transmission to
receiving water bodies downstream.
Traditional methods such as the
platform-bank model and associated
adaptations seek to control and direct
water movement off of the landform
quickly, and to achieve geotechnical
stability by inhibiting all mass transfer
associated with erosion-induced
movement of sediment (Nicolao,
2003). Note that the above statistics
are not indicative of the performance
ability once constructed.
Goal:
Physical stability of waste rock
dump(s)
