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 Colorado closed in accordance with the design criterion: stability for 1,000 years to the extent reasonable, and at any rate for 200 years.  A long time ago I walked the lands of the southwest with a professional geomorphologist as we sought to characterize the landforms, erosion processes, and changes of topography in the last 10,000 years and tried to apply these observations to the prediction of the next 1,000 years of topographic change.  We then formulated the conceptual designs for the 24 piles that constitute the Title I UMTRA Project. 

 

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 British Columbia write about wrap-around waste piles, and O’Kane engineers promoting natural geomorphic shapes for their clients’ mine waste disposal facility closure.  And the geomorphic approach has a new and profound application in the Oil Sands—the difference is a move away from the requirement for long-term geomorphic stability to an even more profound application of geomorphic response equilibrium.  I quote:  “It is preferable to create a mature landscape on mine closure, so that the expected rate of change will be comparable to the reclaimed landscape in geologic time.”

 

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 United States, Beersing et al. in the paper A Geomorphic Approach for the Design of Drainage Systems on Reclaimed Mined Area establish these criteria for replicating natural analogues in the design of reclamation drainage systems:

·       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 East St. Louis and the gullies that have been developing for 10,000 on the badlands of the western United States.  I have wondered at the deep new gullies that develop in one winter on reclaimed mines in Idaho.  Sawatsky and Tuttle write of the factors involved in gulley formation in Occurrence and Growth of Gullies on Mine Disturbed Land.  In this fact-filled paper, they note that the primary causes of gulley formation at Syncrude are an absence of vegetation and terrace ponding.   They also note self-healing gullies; i.e., those where gravel and/or vegetation accumulate and inhibit continued growth of the gulley. 

 

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.

Ø     Strategies for reclamation of tailings impoundments.