TECHNOLOGY REVIEW
Oil
Sand Reclamation
Revision: November 2006
Author: Jack Caldwell
http://technology.infomine.com
InfoMine
has posted twelve technical papers by Les Sawatsky and his many coauthors in
the InfoMine Library. You can access
them through the Library using the author’s name as a keyword or via the author
search.
Because
of the technical significance of these papers both to reclamation of Oil Sands
mines and the greater mining industry, we summarize and survey the papers in
this review. The primary focus of the
papers and hence of this review is the application of the principles of
geomorphology to mined land reclamation.
By
way of background, I admit to great sympathy with the geomorphic approach to
design of mined land reclamation works.
Recently I visited three uranium mill tailings piles in
Our
ideas and approaches did not gain currency outside the uranium tailings
remediation arena because of concern for the costs of the works we designed and
constructed. And this is understandable. But the tide seems to have changed: now we
see
The
basic plea and principles are set out by Sawatsky et al. in the paper Integrated Mine
Water Planning and for Environmental Protection and Profitability. In this paper the authors plead for
multidisciplinary input, acceptance of environmental and economic goals,
partnership amongst planners, designers, operators, and regulators, acceptance
of water issues being equal to mining concerns, innovative solutions at an
early stage of mine planning, a sound understanding of natural analogues, data
collection and monitoring, inventory of baseline fluvial and geomorphic
conditions, early establishment of design criteria, and planning by iteration.
These
ideas are further explored in the paper by Sawatsky and Beakstead Geomorphic
Approach for Design of Sustainable Drainage Systems for Mineland Reclamation. Here the authors point out that uniform
landscapes are immature and that rivers meander, balance develops between
erosion and sedimentation, and that flood plains attenuate flows. The authors call for application of these
obvious geomorphic facts in the design of mined land reclamation works.
In
their paper,
Mine Planning Guidelines for Developing
Sustainable Drainage Systems, Sawatsky et al. posit these guidelines:
·
To the extent
reasonable, pre-development surface flows to receiving waters should be
restored; for example they recommend that the ten-year flow to receiving waters
should not exceed the pre-development flow by more than thirty percent.
·
Avoid
side-hill diversions that may be blocked by ice, beaver dams, or sediment.
·
End-of-mine
lakes should be at the end of flow paths.
·
Liquid
impoundments, including final tailings ponds, should be below grade.
·
Final grades
should be less than pre-development grades to account for the greater
erodabilty of the reclamation soils.
·
Major drainage
courses should be on undisturbed ground at low gradients that limit erosion.
The
principles are applied as described in the paper Natural
Analogs For Sustainable Landscape Design at Syncrude, Keys et al. establish
these criteria:
- Create a
geomorphically mature reclamation landscape.
- Create a robust
landscape---one which improves in stability with time.
- Create a landscape
that mimics natural systems in the area.
- Use Best Available
Demonstrated Control Technology.
- Invoke a
design-for-closure philosophy to be implemented in design and operation.
They
expand on the application of these principles in practice, including providing information
on the geomorphic processes and rates operative in the area of the mine, the
design of mine lakes, accommodation of beaver dams, placement of rip-rap to
control stream erosion, aeolian erosion of tailing piles 60 m above the natural
landscape, and post-mining maintenance and monitoring.
Writing
of the application of the principles discussed above to a coal mine in the
·
Robust,
self-healing capacity provided by several lines of defense against sustained
erosion.
·
Ready supply
of armoring material where erosion has occurred.
·
Adjustment of
channel size and shape to handle peak flows.
·
Gradual
evolution.
·
Sediment
balance.
·
A stable
configuration that is not vulnerable to rapid change.
In
an eloquent plea for the adoption of rational sediment yield criteria to mine
land reclamation, in the paper A Strategy for
Determining Acceptable Sediment Yield for Reclaimed Mine Lands, Bender
et al. set out these criteria for a sustainable landscape:
- Provide terrain
suitable for appropriate terrestrial ecosystems.
- Produce similar
runoff characteristics to the natural hydrologic regime of downstream
receiving waters.
- Provide landscape
features that are not susceptible to high rates of erosion such as results
from gully formation.
On
the basis of a detailed examination of the factors that affect the health of
receiving waters, the authors conclude that the following guidelines should be
used to establish acceptable sediment yields:
- Avoid significant
changes in sediment yield, where a significant change may be quantified as
two to ten times background.
- Limit the risk of
high suspended sand concentrations to short durations.
- Provide equal of
better habitat for species spawning, feeding, and overwintering.
Gullies
are the main source of eroded soil from a mine or any slope that is steeper
than the natural surrounding topography.
We have all seen the severely gullied slopes on many a mine waste
disposal facility. I have walked the
1,000-year old gullies of the Cahokia Mounds in
In
many ways these earlier papers by Sawatsky and coauthors are but a run up to
the 2004 paper where their developed and more mature ideas are set out. I cannot quote all I would like to from the
papers by Sawatsky [alone this time] entitled Reclamation
Strategies that Address Mine Closure Drainage.
But if you choose to read only one
paper, this is the paper I recommend. Here
are some quotes that caught my attention:
- “Unlike natural
landforms that have been subjected to 1,000s of years of natural erosion
and sedimentation, constructed landforms are vulnerable to relatively high
rates of erosion if the topography is not contoured to suit shapes that
represent a dynamic equilibrium in natural systems.”
- “Mine disturbed
land is composed of steeper terrain, reduced topographic complexity, and
thin cover layers of organic soil relative to pre-development conditions.
Without mitigation such features result in higher flood peaks, reduced low
flows, and reduced water retention to support vegetation. This might result in increased erosion,
reduced vegetation productivity, and inferior aquatic habitat.”
- “A common
misunderstanding is that terraces prevent erosion. Although terraces intercept runoff
during low intensity storms, erosion can only be controlled if the
accumulation of surface water does no exceed the storage capacity on the
terrace or if the resulting spillage is properly controlled by a spillway
structure.”
This
paper is full of many checklist, practical design advice, case history wisdom,
and reality-base advice. I recommend it
if your business in mined land reclamation.
Here
are the other four papers by Sawatsky that I do not review—not because they are
not good (if you can follow the multiple negatives) but because they are not
apposite to the topic of this piece.
Nevertheless, I recommend you access them and read them:
Ø Toward minimizing the long-term liability of reclaimed mine sites.
Ø Design of a rainfall simulator to measure reclaimed surfaces.
Ø Water erosion prediction for a tailings surface using the WEPP model.