This is a response to an opinion piece written by the SkeenaWild Conservation Trust called “We only say ‘no’ when we need to” that was published June 15, 2016.
It stated, “…we do have serious concerns about tailings dams being constructed in the same manner as Mount Polley, as is proposed for the Seabridge Gold project.”
This statement is factually incorrect. The selected tailings management design for the Kerr Sulphurets Mitchell (KSM) project northwest of Stewart is the best available tailings technology (BATT) to account for the site specific characteristics present in northwestern B.C. and is designed to promote both physical and chemical stability of the waste material.
All potential tailings disposal methods including dry stack and wet disposal methods were reviewed and assessed as a requirement of the recently completed independent Environmental Assessment (EA) process for the project.
Specifically, the KSM tailing management facility (TMF):
* underwent a comprehensive environmental assessment process and the TMF design was changed to reflect input from local First Nations and regulators.
* is located in a confining valley with cross valley dams situated at each end;
* will consist of simple cyclone sand dams at a 3:1 slope with 1 km of dry beaches between the water and the dam, thus minimizing the impact of water within the impoundments;
* has a process and design which allows for discharge from the TMF, thus preventing a buildup of surplus water within the TMF;
* and used 30-day flood event as the design basis for the facility which will result in 12m of freeboard (the height from the water level to the top of the dam) within the TMF.
Additionally, Seabridge has established an Independent Geotechnical Review Board (IGRB) to provide independent, expert oversight, opinion and advice to Seabridge on the design, construction, operational management and ultimate closure of the tailings management facility and water storage dam.
The initial IGRB review of Seabridge Gold’s KSM Project design was conducted in March 2015 and was developed to answer five questions: (1) Are dams and structures located appropriately; (2) Are dam sections, materials, construction methods and sequencing appropriate for the site; (3) What are the greatest design, construction and operating risks; (4) Are the facilities designed to operate effectively, and (5) Are the facilities designed to be safe? The board concluded it was satisfied with the project’s designs and responded favourably to all five questions. Additionally, the board presented a series of recommendations for Seabridge to consider during the ongoing engineering design of the KSM Project as development continues.
Seabridge Gold has made publicly available on our website (www.ksmproject.com), a significant amount of information about its proposed KSM project’s tailings management facility, including the IGRB’s report. We encourage anyone who has questions about the project to view our website.
R. Brent Murphy, P.Geo,
Vice President, Environmental Affairs, Seabridge Gold, Toronto, Ontario
The above letter from Seabridge’s Brent Murphy was emailed to SkeenaWild’s Greg Knox resulting in a reply. It’s contained below.
And thank you for the information.
Unless something has changed with your project, I maintain that my statement is correct. The construction material for your project is earthen dam, using centre-line construction – the same as was used at Mount Polley.
It is also important to note that the KSM tailings lake dams will be 273 meters high. One of the highest earthen dams in the world, more than 6 times the height of the Mount Polley tailings dam (35 m), containing 28 times the amount of tailings as Mount Polley.
You mention that KSM will be using the best available technology. The best available technology according to the Mount Polly review panel is “dry tailings”, or paste technology, not “wet” tailings which is being used at KSM:
Here are their recommendations:
“The goal of BAT (Best Available Technology) for tailings management is to assure physical stability of the tailings deposit. This is achieved by preventing release of impoundment contents, independent of the integrity of any con- tainment structures. In accomplishing this objective, BAT has three components that derive from first principles of soil mechanics:
Eliminate surface water from the impoundment.
Promote unsaturated conditions in the tailings with drainage provisions.
Achieve dilatant conditions5 throughout the tailings deposit by compaction.” (Expert Panel, 2015, p. 121)
Further, the centre-line type of earthen construction (from your EA submissions) that KSM will be using is not even the best available technology for constructing wet tailings impoundments. Centre-line construction is a compromise between the cheaper, yet geo-technically riskier, “upstream” method, and the costlier, yet most stable, “downstream” method (Engels 2013).
Engels, J. 2013. Conventional impoundment storage – the current techniques. Available: http://www.tailings.info/disposal/conventional.htm via the internet. Accessed 11 December 2013.
Below is some further information from a recent Centre for Science on Public Participation report on the issue:
The basic characteristics of the Tailings Storage Facilities (TSFs) for the 4 large transboundary mining projects are summarized in Table 1. The critical factors, from the per- spective of potential for catastrophic failure at some point between the operation stage and 10,000 years7 in the future, are:
Dam height – the higher the dam the larger the po tential for tailings release during a failure;
TSF capacity – like dam height, the larger the TSF ca pacity, the greater the potential for tailings release during a failure;
TSF construction design – there are three types of dam construction design: (1) upstream, the least safe; (2) downstream, the safest; and, (3) centerline, safer than upstream, but not as safe as downstream (see Figure 2 for illustrations of these construction meth- ods);
Figure 2 – Tailings Dam Construction Types: (a) Upstream, (b) Downstream, (c) Centerline
TSF design criteria – has the dam been designed to survive the largest earthquake or flood it could experience during its design life;
and,TSF closuredesign–will the tailings be saturated ordra inedaft erclosure?
The Expert Panel recommends drained tailings. TSFs with lakes on top after closure pose the greatest risk for catastrophic damage if a dam failure were to occur.
KSM is large copper-gold porphyry, and if developed would probably be the largest mine in British Columbia. KSM contains mineral reserves that are planned for both open pit and underground mining.
The tailings impoundment would require two large dams, the tallest would be 6 times as high as the failed Mount Polley dam, and would contain 28 times the amount of tailings (see Figure 3). In the middle of the main impoundment would be a smaller, lined repository for the high-sulfide tailings from the final concentrator circuit (see Figure 4). The TSF is planned for a wet closure (saturated tailings) to inhibit acid generation (see Figure 5).
An Environmental Assessment Application was submitted to the provincial and federal regulatory authorities in early 2013 and received final approval from the Canadian Federal Government in December, 2014, after having received approval from the Province of British Columbia in July, 2014. However, construction has not been started, nor has a start date been identified. Financing is still needed for this project. The proposed tailings dams are centerline-type con- struction, like that at Mount Polley, and a wet closure is planned for the potentially acid generating tailings (KSM, 2013).
Does this design meet the recommendations of the Expert Panel? No. The primary problem is that this design incor- porates a wet closure, with active ponding of water on top of the tailings that will keep them permanently saturated. Permanent saturation, while providing the best approach for the prevention of acid mine drainage, also means that the tailings are vulnerable to mobilization if there is a dam failure.
Can this design be altered to meet the recommendation of the Expert Panel? Yes. The BAT Expert Panel recommendation can be met if the North and South impoundments of non-acid generating tailings were drained to provide long-term stability, even if the central sulfide residue cell were left permanently saturated in order to inhibit acid generation, the
North and South drained impoundments would provide sufficient long-term protection for the saturated residue im- poundment to meet the requirements of the Expert Panel.
Construction on this mine is still in the indefinite future. There is still time for design changes to the TSF that could incorporate drainage for the non-acid generating impoundments that would be very easy from a technical and cost perspective. However, at present there have been no public discussions about this possibility.
This concludes the further information from a recent Centre for Science on Public Participation report on the matter.
SkeenaWild Conservation Trust.