This blog is about the content of the presentation and not the forcible removal of an attendee that ensued during the second presentation on May 23rd. It took considerable time to separate the content and intent of the presentation from the events of that evening. Coverage of the event and ensuing fall out may be found in the media mentions section of the goldmineconversation blog and the NOPECampaign on facebook.

It is critical to understand the nature of the tailings dam itself and the method and form by which the tailings will be disposed of within the dam.

Atlantic Gold did organize the event and did agree to hold a second meeting once they realized that public consultations are not confined to Atlantic Gold’s office staff’s working day. This opportunity was not afforded the communities impacted by the Touquoy Mine and the proposed Beaver Dam and Fifteen Mile Gold Stream Projects.

This blog will be presented in two parts; the first is about the presentation itself with some added research to help the reader better understand and visualize the various types of dams. The second part discusses in greater detail the design and approach AG has proposed to undertake and how this compares to other available options. Additional references supporting the blog content may be found by clicking on the underlined sections within the blog. This will open in a separate window.

As you read through the material think about the following:

  • The life of the mine is 5.5 to 6 years.
    • How is the choice of a tailings dam design option affected by a short mine life?
  • What are the operating, capital costs, and reclamation costs of the various dam designs and tailings delivery formats. How are these costs managed to provide maximum profit to the shareholders and what are the costs of these options to the environment and community?
    • As lowest cost producer in the industry:
      • What is being sacrificed to achieve the lowest cost producer claim?
      • How does each design option affect the reclamation costs at the end of the life of the mine? Are the costs deferred to a time when fiscal resources are dwindling leaving a deferred liability?
  • How is the water being managed? What impact does the design choice have on the water balance, water quality and quantity, and the surrounding environment?
  • It is critical to ask where is the material coming from to build the dam embankments , what is the sulphide content, metal content and acid generating potential of all materials ? If local rock is used(it is the cheapest option), these contents and potentials will change, laterally, vertically and with each location.
    • What is the sulphide content of the disposed tailings? What is the pH of the disposed tailings? How frequently will this be monitored? Does the company monitor this themselves?
    • The legacy tailings MUST be accurately mapped! Can this material makes its way into a tailings embankment?
  • What has caused previous dam failures?
  • What additional design features could added to mitigate/prevent seepage/leaching into the groundwater and surface water? e.g. geomembranes.
  • Can you rely on the government to ensure that the interests of the community and environment are protected? British Columbian’s realize that this is not the case.

ITRB Presentation:

There were about 75 individuals that attended this session. My intent was to listen to the first presentation and let others in the audience ask their questions. If the second session was not full, I had hoped to get my questions in then. As it turned out, I was able to ask Mr. Millard and Mr. Jansons some questions in-between sessions.

The background and utility of a ITRB may be found in a previous blog. The tailings dam is of major concern for the community. There has been numerous questions posed to Atlantic Gold on this aspect of the proposed project, all of which have remained unanswered. Questions regarding the choice of the location for the tailings management facility and what analysis went into the choice of the preferred location were not answered in this presentation.

Purpose of the Information Session:

The Atlantic Gold information session notification indicated that the trio were there to only answer questions relating to best practices for the design, construction and operations of tailings management facilities. The lack of previous opportunities for the community to engage managers from Atlantic Gold face to face, more than likely led to community members frustration and off topic questions. The Community Liaison Committee may be better informed than the greater community and if so, could be providing updates in a town hall type setting such as was the case for this presentation.

Role of the ITRB Members With Respect to Atlantic Gold:

Although not a regulated requirement in Nova Scotia as it is in British Columbia, Atlantic Gold (Atlantic Mining NS Corp) brings in this trio twice? a year to review the safety of the tailings management facility (TMF) at the Touquoy Mine in Moose River. I was surprised by this and I am guessing this was suppose to demonstrate to the community that there is an additional level of oversight for the design, construction and operational phases of the dam embankment. The panel did emphasize during the course of the presentation, that their reputations are important to them. When questioned as to whether they have ever not approved or “walked away” from a dam design for environmental reasons, the answer was essentially; there were times, although rarely, that the economic feasibility of making the tailings dam safe did not justify the Company moving forward.

The presenting panel members are “independent” assessors of the TMF, but are paid to do so by Atlantic Gold. Someone on the panel noted that the conditions of the industrial permit for the Touquoy Mine stipulate that this review be conducted, the frequency of which was not clear.

This group are not designing the TMF for Cochrane Hill, nor are they recommending how the TMF will be constructed, however they will be reviewing the design. Knights Piesold Consulting is the engineering firm engaged by Atlantic Gold to design the tailings management facility. Oops, …. this company is one of several companies at the centre of an Imperial Metals lawsuit over the Mt. Polley Dam failure.

What first stood out to me were the words of the principal presenter from the ITRB, not verbatim but close to “It seems every river in Nova Scotia is special”., a not so quiet hush fell over the crowd. This clearly demonstrated the lack of understanding on part of Atlantic Gold and its paid consultants, independent or not, the importance of the St. Mary’s River and the role that the river plays in conservation, preservation of species at risk, education and recreation.

TAILINGS DAM DESIGN OPTIONS:

The ultimate purpose of a tailings impoundment is to contain fine-grained tailings left over from processing the gold ore. There are two basic types of structures used to retain tailings in impoundments; the raised embankment and the retention dam. A raised embankment is proposed for Cochrane Hill. The four main types of impoundments include the Ring-Dike(type proposed for Cochrane Hil) , In-Pit, Specially Dug Pit, and variations of the Valley design. The design choice is primarily dependent upon natural topography, site conditions, and economic factors.

Because costs are often directly related to the amount of fill material used in the dam or embankment (i.e., its size), major savings can be realized by minimizing the size of the dam and by maximizing the use of local materials, particularly the tailings themselves. Raised embankments (such as proposed for Cochrane Hill) are constructed in phases as the need for additional disposal capacity arises. Raised embankments begin with a starter dike with more height added to the embankment as the volume of tailings increases in the impoundment. They have a lower initial capital cost than retention dams because fill material and placement costs are phased over the life of the impoundment. The choices available for construction material are increased because of the smaller quantities needed at any one time. Raised embankments can use natural soil, tailings, and waste rock in any combination.

When reviewing the draft environmental impact statement(EIS) for Cochrane Hill, the community needs to ensure that the acid generating potential, heavy metal content, sulphide content of materials that could eventually be used to the raise the dam are initially adequately assessed and documented within the EIS and that AG are required to be monitor these values over the life of the mine and post reclamation. Request that these results should be made public; as in most cases they are not. Remembering that the use of local material is the cheapest option for constructing the dam; stockpiled till cover, overburden, mine waste rock and legacy gold mine tailings have the potential to make their way into the impoundment!

Mr. Peter Lighthall’s from the ITSB panel was the main presenter. He pointed out that tailings dams are not water dams. He reviewed the different types of embankment dams and the pros and cons of each are highlighted below:

Upstream Tailings Dam Mt. Polley
Upstream Dam

Upstream Tailings Dam – These are built progressively “upstream” of the starter dam by incorporating tailings materials into the dam for support, through the controlled deposition of tailings. Upstream designs start with a free draining starter wall as the foundation. The tailings are then discharged into the dam, which then harden to form the foundation for the next level of wall. Ensuring water is properly removed and recycled is a crucial element of maintaining the structural integrity of the wall.

Using existing tailings reduces construction costs of the dam, however they are less stable than other designs under static loading and in the event of an earthquake, because tailings materials may liquefy (like cake batter) and lose their strength.

These types of dams are suitable for facilities in areas of low rainfall, low seismic activity and relatively flat terrain.

Centreline Tailings Dam Cadia-Ridgeway Dam – Australia
Centreline Dam

Centreline Tailings Dam – These types of dams are raised progressively while maintaining the original centreline of the starter dam. They usually have an impervious core, which is supported by a localized zone of compacted tailings, and an internal drain or filter. The centreline method is a hybrid of upstream and downstream designs. When the wall level is raised it is built on top of both the tailings and the existing wall. In contrast to the downstream design, the centreline remains the same throughout the subsequent raises.

These types of dams require less material than downstream and are more stable than an upstream dam in the event of an earthquake. Hydro-cycloning of plant tailings is an often used tool to produce relatively coarse free draining sand for Tailing Storage Facility (TSF) embankment construction.

According to Mr. Lighthall, Atlantic Gold plans to use the downstream method of construction with three embankment walls and a solid wall of mine rock(impervious starter wall?). From what was indicated at the presentation, Stantec is the Engineer of Record(EOR) for the tailings dam. The height of the dam is at this point is anticipated to be 47 metres high from its base, although the project description has conflicting height levels. This will change if the ore reserves and life of the mine are extended beyond the 6 year life.

Downstream Tailings Dam China – Note Use of Geo-membrane liners that reduces chemicals from leaching into the soil or groundwater

Downstream Tailings Dam – Downstream designs start with an impervious starter wall. The tailings are then discharged into the dam and as the embankment is raised, the new wall is constructed and supported on top of the downstream slope of the previous section. This shifts the centreline of the top of the dam. The phased nature of raised embankments makes it possible to attempt to address problems that may arise during the life of a tailings impoundment. The downstream design was developed for areas with seismic activity and high rainfall or water collection.

These tailings dams require more material over time to build increasing the construction costs of the dam. One member of the panel noted that in Nova Scotia the material in the tailings dam construction must not contain acid generating materials.

In the case of Cochrane Hill the acid generating potential of the site material is being investigated by AG. If material is acid generating or does not meet the maximum guideline for sulphide content, material would have to be trucked in from another location (expensive). Alternatively, in some regions the sulphides go through a cyclone to remove these materials, then it is suitable to use as materials in the dam. My conversation with Mr. Millard of AG indicated that the presence of calcium carbonate within the Meguma host rock has the capacity to buffer or lower the acid generating potential of a sulphide bearing rock, such apparently is the case at the Touquoy Mine. This will be the crux of the argument for using local material within the dam at Cochrane Hill. The calcium carbonate content of the various formations and horizons of the host rock will vary horizontally, vertically and geographically.

Is the material present at the Cochrane Hill location in sufficient quantities to buffer or lower the acid generating potential of the sulphide bearing rocks? Testing to prove this will have to be extensive, watch for this in the EIS. According to a geologist friend of mine, while reviewing Meguma drill core from other regions, they were specifically asked to look for the minerals ankerite and calcite, which are calcium carbonate minerals.

In a future blog, I will summarize a conversation I had with Peter Lund, he referred me to a paper he wrote on the subject of acid mine drainage at the Halifax Airport. This lead me to a PHD thesis from Don Fox, his work indicated that if the calcium carbonate contains others elements such as iron, magnesium or manganese, the buffering capacity of the calcium carbonate is lowered. Ankerite is a iron, manganese, magnesium carbonate. The thesis also pointed out that the mineral pyrrhotite is worse than pyrite or arsenopyrite. When submitting questions or comments on the EIS ask for the mineralogy of the sulphide minerals found in the rocks at Cochrane Hill. Mr. Lund indicated that the key to acid mine drainage is to keep the pH of all material to a 4.5 or above. His work indicated that although arsenopyrite were in rocks at the airport, the low pH lead to the release of aluminum from the Meguma rock and this produced the fish kill in the river adjacent the airport.

Once again as you read the draft EIS, ensure that the document contains extensive analysis of all materials on site. Additional items to watch for pH values, aluminum and pyrrhotite. How will AG keep pH above the 4.5, is aluminum being monitored, is pyrrhotite present in the sulphides?

Downstream tailings dams do not require support from the tailings placed against the core, however tailings placed upstream of the core reduces the hydraulic gradient through the core zone. This can be achieved by using the hydro-cyclone method described above.

Downstream Tailings Dam

REVIEW OF TAILINGS DAM FAILURES –

The presentation also reviewed several examples of the upstream and centreline tailings dams that failed and what led to the failures.

Listening to Mr. Lighthall’s presentation on the results of past forensic reviews of various tailings dam failure, I was struck by the causes of the failures:

Recent major tailings dam failures have led to an industry-wide review of the design and management of tailings storage facilities. Mr. Lighthall also reviewed what has transpired in Canada post the Mt. Polley’s tailings dam failure. The Mining Association of Canada, has implemented a tailings management protocol, the latest version 2019 may be found here.

Mr. Lighthall, also spoke of the concept of Engineer of Record (EOR) stating that all tailings storage facilities must now have an engineer of record. The EOR for Cochrane Hill is Stantec, but the tailings storage facility design engineer is the firm Knight Piesold. When asked if the EOR was fiscally liable for a failure, the answer was no, the Engineer of Record link above discusses what it means to be the engineer of record for a tailings storage facility. In conclusion, the designation of an EOR by Atlantic Gold for Cochrane Hill will not provide the community with sufficient security and liability responsibility to justify approval of the Cochrane Hill Gold project.

It appears that in part, due to reasons highlighted above, that the designing engineers or EORs lack control at the day to day level within the operating Company. There were apparently 4 EORs for the Mt. Polley tailings dam and as a former mine tailings foreman for the company points out : he lays the blame at the company and government level. This video is extremely revealing in terms of what happens at this level. It would require some strict oversight to ensure that this does not happen. Is it even possible to achieve this?

In late 2016,The International Committee on Mining and Metals (ICMM) commissioned a report on surface tailings management guidance. Overall, it found that modern engineering, design and construction practices adequately prevent structural failures, and that efforts going forward should focus on implementing more robust governance and operating practices at every site.

Based on the report, ICMM issued a position statement that commits ICMM members to minimize the risk of tailings dam failures. The position statement, which was endorsed by all ICMM member CEOs, details a Tailings Governance Framework that includes:

  • Defining accountabilities, responsibilities and associated competencies to identify and manage risks;
  • Maintaining the financial and human resources needed throughout a facility’s lifecycle;
  • Identifying risks, applying appropriate controls and verifying the controls’ effectiveness;
  • Assessing, controlling and communicating the risks associated with potential changes to avoid inadvertently compromising facility integrity;
  • Establishing processes to recognize and respond to impending facility failures and mitigating the potential impacts of a potentially catastrophic failure; and
  • Comprehensively assessing and continually improving controls through internal and external review and assurance processes.

There is no “one size fits all” design solution for tailings dams. Each tailings dam is unique because of the variety of mine site conditions, including the climate and topography, the physical and geochemical properties of the ore and tailings, the amount of water, the impact on water quality, the planned height of the dam and the available construction materials (McLeod 2016).

To reduce the risk of tailings dam failures over the long term, engineers and mine owners must consider:

  1. Minimizing water held in the tailings storage facility, while balancing the need to saturate acid-generating tailings when present.
  2. Thickening or filtering tailings materials (de-watering the tailings).
  3. Widening the dam crest to prevent “slumping” or erosion from minor dam breaches.
  4. Placing cyclone sand upstream and downstream of the core zone to act as a natural filter and to infill natural voids and cracks in the impervious core.
  5. Adding redundant spillways in non-critical areas of the impoundment to manage excess water.
  6. Reclaiming the site at mine closure with vegetation and erosion-resistant surfaces.

With advances in site investigation techniques such as cone penetrometer testing (CPT), 3D geophysical surveys, LiDAR and satellite imagery, and modeling techniques using sophisticated software, the engineers’ design toolkit for tailings dams is rapidly expanding. An independent extensive tailings dam failure modeling analysis should be undertaken for the proposed Cochrane Hill tailings management facility.

Additional References:

The Canadian Dam Association (CDA) and the International Commission on Large Dams (ICOLD), representing the Canadian and global scientific community and industry respectively revised their state of practice guidelines. The ICOLD bulletin on Tailings Dam Technology Updates was published in 2018.

Water Management for conventional means of tailings disposal (AG approach)

Tailings Dam Part 2 Will Discuss the AG approach and the Companies choice of the lowest cost form of tailings disposal, “wet slurry” , not the best available technology. Stay tuned.

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1 Comment

  1. If you read the “Report on Mount Polley Tailings Storage Facility Breach” (January 30, 2015, Section 9), the report states: “Improving technology to ensure against failures [of Tailings Storage Facilities, TSF] requires eliminating water both on and in the tailings: water on the surface, and water contained in the interparticle voids. … Simply put, dam failures are reduced by reducing the number of dams [containing water] that can fail.
    Thus, the path to zero leads to best practices, then continues on to best technology.”
    Later…
    “While best practices focus on the performance of the tailings dam, best available technology (BAT) concerns the tailings deposit itself. The goal of BAT 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 containment structures. In accomplishing this objective, BAT has three components that derive from first principles of soil mechanics:
    1. Eliminate surface water from the impoundment.
    2. Promote unsaturated conditions in the tailings with drainage provisions.
    3. Achieve dilatant conditions throughout the tailings deposit by compaction.
    …The overarching goal of BAT [Best Available Technology] is to reduce the number of tailings
    dams subject to failure. This can be achieved most directly by storing the majority of the tailings below ground—in mined-out pits for surface mining operations or as backfill for underground
    mines. Both methods require integrating tailings planning into mine planning. This has not been common practice in the industry to date, as the Mount Polley case has shown, and the synergies to be achieved are mostly unexplored. Apart from this, surface storage using filtered tailings technology is a prime candidate for BAT.”
    In my opinion, these TSF BAT design options must be considered fully, given the proximity to the St. Mary’s River.

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