Dargues Engineering Contractor Knight Piésold involved in Canadian Tailings Spill

What does this have to do with the Dargues Gold Mine?

Knight Piésold are the engineering contractors responsible for the design of the Dargues Gold Mine’s Tailings Storage Facility (TSF). Almost 900,000 tonnes of tailings will be stored in perpetuity in Knight Piésold’s TSF at the headwaters of the Palerang / Eurobodalla drinking water catchment.

The Mt Polley Disaster

On August 4, 2014, a 4-square kilometer Tailings Storage Facility ruptured near Mt Polley in British Columbia, Canada, spilling tailings and contaminated water (estimates vary from 14 – 24 million tonnes) into the freshwater system: Hazeltine Creek – Quesnel Lake – Quesnel River – Fraser River. After gouging Hazeltine Creek and coating it in grey sludge, the tailings pooled in the formerly pristine Quesnel Lake. From the lake, tailings were entrained for hundreds of kilometers, contaminating not only human drinking water, but the entire food chain (including humans) of that riparian corridor, whose keystone species is the salmon.

A detailed, ground-level assessment of the spill, written by a local indigenous band, is available here: https://imperialnomoredotcom.files.wordpress.com/2016/05/docfoc-com-yuct-ne-senxiymetkwe-camp-initial-assessment-report-on-imperial-metals-mount-polley-mine-tailings-storage-facility-breach.pdf

– Two years later (August 2016), Hazeltine Creek remains deformed and caked in grey metallic sediment, the Quesnel system remains contaminated, no effective clean-up has occurred, nobody has been held to legal or financial account, and the mine is back in full production. The re-opening of the mine has divided the province, and protests are ongoing (see https://imperialnomore.com/ to learn about the public unrest).

Knight Piésold

– The Mt Polley gold and copper mine is owned and operated by Imperial Metals. The failed Tailings Storage Facility was designed by Knight Piésold, who were also the engineers on record for twenty years, and made a strategic withdrawal from the project three years before the collapse. They deny all responsibility for the disaster.

Knight Piésold Disclaimers

– Knight Piésold disclaimers attribute the breach to the steepening of perimeter embankments and the increasing of supernatant pond volume, both of which occurred after KP’s withdrawal from the project.

– They fail to mention the soft layer of glaciolacustrine (also known as GLU or glacial till), underlying the site of the breach for millennia, into which a section of the perimeter embankment suddenly sunk by approximately 5 meters in the early hours of August 4, 2014 (MEM report, p. 158), causing the facility to overtop and rupture.

– Neither investigation cited in the Knight Piésold ‘Fact Sheet: Mt Polley Tailings Storage Facility(bottom of web page) actually vindicates Knight Piésold. Rather, both the Independent Expert Investigation and Review, and the Ministry of Energy and Mines Investigation testify to Knight Piésold’s negligence by demonstrating that the root cause of failure was in the original TSF design, namely the failure to take into account the nature of the ground on which the TSF was built.

– Independent Review Panel: https://www.mountpolleyreviewpanel.ca/sites/default/files/report/ReportonMountPolleyTailingsStorageFacilityBreach.pdf

– Ministry of Energy and Mines: http://mssi.nrs.gov.bc.ca/1_CIMMountPolley/Appendix3.pdf

– The reports show that the overly steep embankment would not have collapsed had it not been built on a layer of geological jelly, whose depth and weakness Knight Piésold either failed to detect or disclose. The Independent Panel uses the metaphor of a loaded gun to describe Knight Piésold’s TSF before subsequent engineers on record (AMEC) allowed the embankment to be raised at too steep an angle.

– The ‘KP Fact Sheet’ claims that the increase in supernant pond volume (water and tailings in the TSF), after their withdrawal from the project, and its proximity to the embankments was a ‘key contributing factor to the erosive development of the breach,’ (KP fact sheet, p. 2). But this erosion only occurred after a section of the perimeter embankment sunk into its foundations by 5 meters, causing the facility to overtop (spill over the embankment) (MEM report, CIM investigation). The erosive action was a sudden ‘tearing open’ of that breach, and was an effect of foundational failure.

– The long-term process of erosion in TSF embankments caused by the contents of a facility (‘supernant pond volume’) is known as ‘piping and cracking’. But both official investigations discount this as a causal factor in the Mt Polley breach. The Independent Review Panel found that ‘piping and cracking, which is often the cause of the failure of earth dams, was not the cause of the breach,’ (IRP Media Release, January 30, 2015). Likewise, Klohn Crippen Berger for the Ministry of Energy and Mines states that ‘the stability of the embankment with regard to foundation failure would not have been affected by piping caused by internal erosion of the core,’ (MEM Summary of Opinions, August 2015, p. 119).

– KP states that it is ‘confident that its designs for each stage of the Mount Polley TSF were appropriate.’ (KP fact sheet, p.2). This flies in the face of the evidence presented in both official investigations which show that the fatal flaw, the glaciolucustrine layer, was present throughout the entire development and was not adequately measured, tested, or understood.

– The obvious must be stated: The site was not appropriate for the establishment of a tailings storage facility due to the weakness of the foundation. Let alone when we take into account the ecological sensitivity, human importance, or former beauty and purity of the freshwater systems and riparian corridors downstream.

Profit Without Accountability

-The Independent Panel’s report shows that the site’s natural foundations were not adequately assessed before, during, or after the construction of the TSF. The responsibility for which must fall to both the mining company Imperial Metals, and their engineering consultants. Especially Knight Piésold, who selected the site, designed the TSF, and oversaw its construction and its first two decades of use.

-Knight Piésold accepted the contract from Imperial Metals to build an enormous TSF, which they endearingly call ‘tailings ponds’, to store tens of millions of cubic meters of toxic waste, where the ground was unstable and where the environmental consequences of failure would be utterly unacceptable (destroying Hazeltine Creek, fouling Quesnel Lake, ‘the cleanest deepwater lake in the world’, and contaminating hundreds of kilometres of freshwater systems with a reeking grey slurry teeming with heavy metals). That they withdrew from the project over twenty years later, when they became anxious about a catastrophe, (‘kp fact sheet’), does not vindicate them. Their complicity is implied ad nauseum by the results of the Mt Polley Review Panel’s report, and stated explicitly in the subsequent investigation by the Ministry of Energy and Mines. Why Knight Piésold has not been co-prosecuted for negligence, along with the owner-operator Imperial metals and subsequent engineers on record, is a mystery deserving of its own investigation.

Why this Matters to South Coast NSW

a) Trust: The owners of the Dargues Gold Mine intend to entrust our water, along with our health and livelihoods, to the designs of a consultant that summarily failed to protect the water, people, and habitats of British Columbia in the course of turning its profits.

b) Ethics: We (Australia) should not supply contracts to a company that was responsible for one of the worst environmental disasters of our time. Especially not when they remain in a state of complete denial over their involvement. They have contributed nothing to rehabilitation of the Quesnel Lake or the riparian corridor upstream or downstream, and offered nothing in the way of compensation to landholders whose property is worthless and whose water is tainted for the foreseeable and unforeseeable future.

Nobody has been held to legal account for the Mt Polley disaster. No charges, no fines, no jail time. If we based our own conclusions on the environmental justice system of British Columbia, we must assume that this entirely preventable, man-made disaster was the fault of the earth itself.

-Knight Piésold has neither accepted nor been imposed one ounce of responsibility, despite rigorous investigations pointing directly at their oversights. To my knowledge, they have done nothing for the fouled Quesnel Lake or River, paid nothing towards the fiction of rehabilitation, and offered nothing by way of compensation to the people of Likely. They have borne no consequence, and heeded no lesson.

-They deserve neither our trust, nor Australian business. Yet Unity Mining intends to entrust our river, our water, our national park, our ecosystems and livelihoods, along with the value of our homes, to the designs of this very company. Not in my name, not in the name of the downstream community whose overwhelming majority is ignored, but in the name of temporary profit to be spent elsewhere. Only tailings will be left to the Araluen Valley, to be suspended in perpetual uncertainty at our headwaters.

A re-cap on the spill itself…

Extract from Letter in Defence of the Deua River, its Ecosystem, and its People
Tom Wells
August 26, 2015 (edited June 21, 2016)

The Reality of a Tailings Storage Facility Failure: The Mt Polley Disaster, Canada

I was witness to the immediate effects of the Mt Polley tailings spill of August 4, 2014, as seen from a commercial rafting expedition entering the Fraser River days after catastrophic failure of the Tailings Storage Facility engineered by Knight Piésold and owned and operated by Imperial Metals. I will therefore give my own testimony as to the immediate consequences, as observed with my own senses.

The Mighty Fraser River is the main artery of British Columbia, uniting the collective water of thousands of tributaries and escorting them to the Salish Sea at the metropolis of Vancouver. I’d rafted, kayaked, and swum in the Fraser hundreds of times before, and although brown with silt and the combined shades of its myriad waters, and although cattle farms dot its drainage, it was free from pollution detectable to human senses. The Fraser’s immense volume (100,000 – 300,000 cubic feet [or 2,830 – 11,326 cubic meters] per second at normal flows) was its coping mechanism against contaminants, and until that August it had supported a healthy salmon run every autumn. The Fraser’s salmon stock is one of the largest in North America, and has supplied bands of First Nations (indigenous Canadian) people for millennia. Their dependency on fishing the Fraser and its tributaries continues to this day. Bald and golden eagles, osprey, black and grizzly bears, also live or die by the health and numbers of the Fraser’s salmon.

When our expedition met the Fraser via at its confluence with the Chilcotin (some 200 river kilometres downstream of the Mt Polley tailings facility), we’d been on-river and isolated from all outside contact for five days. I didn’t know the Mt Polley Tailings Storage Facility existed, but my ignorance had no bearing on its burst embankment or the 14.5 million cubic metres of the toxic slurry spilling into the formerly pristine Quesnel Lake and its drainage, the wild, crystalline Quesnel River. The flood of effluent, containing concentrated levels of arsenic, lead, nickel, and other heavy metals (many of which will be present in the Tailings Storage Facility planned for the Dargues Mine), coursed through the Quesnel River’s 50-odd kilometres and joined the Fraser some 150km upstream of our location. It was teeming under our rafts. Although the cause was unknown to me at the time, I didn’t need a governmental water analysis or belated disaster declaration to tell me that something was very wrong. The moment we entered the Fraser, an unfamiliar, septic waft invaded my nostrils. It smelled like an infected wound, singed the throat like bile, and left a yellow-green foam spinning in eddies. When we reached our take-out, we lifted the rafts from the water and discovered a film of green mucus clinging to their undersides.

The Fraser was flowing at well over 100,000 cubic feet per second that day (well over 3,500 cubic meters per second – Water Office: Hydrometric Data). And yet the dilution was insufficient even to mask the effluent from my own unaided senses. The Deua River, by comparison, flows through the Deua National Park at a mere few hundred cubic feet per second. During dry periods, it barely flows at all. It has negligible power of dilution for an industrial scale spill of any waste material. Furthermore, when Dargues TSF reaches its 900,000 tonne capacity, the proportion of tailings to Deua riverwater would be more than 20 times greater than the proportion of spilled Mt Polley tailings solution (14.5mt) to Fraser riverwater.

As we loaded the reeking rafts into the trailer, the Fraser salmon run was just beginning. First Nations People fished from the shores. Black bears were on their way to the riverside too, looking for an early salmon. Eagles and osprey circled overhead, awaiting their catch. The entire food chain was contaminated.

The effects upstream were apocalyptic. Hazeltine Creek, which bore the immediate outflow, was inundated with a grey-brown sludge so voluminous that it tore trees from the earth and carved the creekbed into new dimensions. The Quesnel Lake below, ‘the cleanest deep water lake in the world’ (Wiki: Mt Polley Disaster) became the tailings storage facility, and the Quesnel River its overflow gutter. Ground zero is permanently disfigured, and the chemical fallout could last centuries or millennia. The salmon run, along with all aquatic life, were decimated. The value of houses and property in the region plummeted, tourism ceased, and the local community drank water from plastic bottles. Early estimates regarding the cost of ‘clean-up’, supposing such a thing were actually possible, were as high as $500 million, with current estimates reaching $1 billion (The Wilderness Committee). Imperial Metals had bonded only $14.5 million against environmental damages (Vancouver Observer).

The ‘bottom line’, irrespective of the environmental tragedy: the mine will cost more to the community, and the nation, that it ever has, or ever will, contribute over its lifetime.

An update of the effects of the Mt Polley disaster one year on (August 2015), can be found here: (The Wilderness Committee: Mt Polley one year on).

First Denial of Accountability: Knight Piésold
Statement by Knight Piésold Ltd. regarding the Mount Polley Mining Incident
August 8, 2014 (4 days after the disaster)


Second Denial of Accountability: Knight Piésold
September 22, 2015
http://www.unitymining.com.au/wp-content/uploads/2013/05/19-DRCCC-Meeting-Minutes-March-2016_FINAL.pdf (and scroll down to the attachment)

Extract from Modification 3: Impacts on Species
Tom Wells
April 18, 2016

The failed Mt Polley TSF was designed by Knight Piésold, the engineering firm contracted by Unity Mining to design the TSF near Majors Creek. It is Knight Piésold’s design upon which the security of the Eurobodalla Shire’s most important freshwater source will largely depend if the mine is allowed to proceed (i.e., if Modification 3 is approved).

Note: Knight Piésold was Complicit in the Mt Polley Disaster: In addition to designing the Mt Polley TSF, Knight Piésold were also the engineers on record from 1989 to 2011. They began withdrawing from the project in 2010, when ‘the embankments and overall tailings impoundment [were] getting large’, (Knight Piésold Fact Sheet: Mt Polley Tailings Storage Facility, 2015).

Knight Piésold denies all responsibility for the disaster of August 4, 2014. They blame subsequent engineers and the owner-operator Imperial Metals, claiming that they raised the wall embankment at too steep an angle (1.3 Horizontal: 1 Vertical, compared to Knight Piésold’s 2H:1V – Knight Piésold Fact Sheet). While the over-steepness of the walls is acknowledged as a factor by the official Mt Polley Independent Expert Investigation and Review Panel, they concluded that the underlying cause was actually ‘foundational failure’, without which the over-steep wall would have continued to stand.

A separate investigation by the Ministry of Energy and Mines confirms that foundational weakness was the first causal factor in the collapse: ‘The mechanism of failure was the embankment sliding on a weak layer of clay located approximately 10m deep in the foundation of the dam… the dam slumped (dropped in elevation) approximately 5m, which led to overtopping and erosion of the dam,’ (p. 158).

Knight Piésold continue to deny any responsibility despite their documented and apparent failure (detailed in the MEM report on pages 20-21, 43-45, and 139) to properly assess the geological foundations of the facility throughout their involvement, namely the depth and nature of a soft layer of glaciolacustrine (also referred to as GLU or glacial till). ‘A root cause of the failure was an inadequate interpretation of the foundation geology, which was influenced by an inadequate site characterisation… the glacial history of the dam foundation was not adequately understood.’ (MEM, p. 158). In other words, no Tailings Storage Facility should ever have been built on Mt Polley.

Knight Piésold cannot learn from what they deny. Indeed, Dr Beck of GHD identifies similar negligence in their assessment of the Dargues foundations: While some investigations were undertaken as part of the original approval there was no detailed soil property assessment […] Further the Knight Piésold report 2015, clearly states that the TSF soil liner design was based on assumed rather than measured soil properties, (GHD, Proposed Dargues Reef Mine, Modification 3: Comments on Response by Proponent, p. 10).

Knight Piésold’s Complicity in the Mt Polley Disaster: Investigation Extracts

The extracts below are from the Independent Review Panel and Ministry of Energy and Mines Investigations. They demonstrate that design oversights (referring to the original design) were the principle cause for the collapse of a section of the perimeter embankment on August 4, 2014. Note that although the Panel prefers not to refer to ‘the designer’ by name, the company in question is Knight Piésold.

The investigations also show that the first cause of failure cited by Knight Piésold in their ‘fact sheet’ (Dargues CCC meeting 19, appendices), namely the raising of the perimeter of the wall at too steep an angle after KP’s departure from the project, was a secondary and compounding factor, a ‘trigger’ to an already ‘loaded gun’. The concurrent increase in supernant pond volume (water and tailings), cited by KP as ‘contributing to the erosive development of the breach’, is shown by the investigations not to have affected dam integrity. There is no evidence that the process of liquid penetration into the embankment, also known as ‘piping and cracking’, was a factor in the breach. Further, the investigations show that no number of third-party dam safety reviews (such as those mentioned by KP in their statement of August 8, 2014) could have been expected to detect the ‘hidden flaw’ of foundational weakness as they are not of the scope to drill for subterranean soil samples. It was Knight Piésold’s responsibility as the engineers immediately responsible for design and oversight of the facility to drill, collect, and analyse samples in order to establish the strength of their foundations, or lack thereof.

Official Investigation 1: Independent Review Panel
Report on Mt Polley Tailings Breach
January 30, 2015


6.5 CAUSES OF FAILURE (p. 105)


The dominant contribution to the failure resides in its design. The design did not take into account the complexity of the sub-glacial and pre-glacial geological environment associated with the Perimeter Embankment foundation. As a result, foundation investigations and associated site characterization failed to identify a continuous GLU layer in the vicinity of the breach and to recognize that it would be disposed to undrained failure when subjected to the stresses associated with the Dam.

At the time of Stage 4 (2006 – 2007), Knight Piésold (KP) had proposed a design for the Perimeter Embankment with a 2H:1V downstream slope and raises of the core and filter with a parallel inclined alignment to El.965 m. This design has been projected in Figure 6.5.1 to the core elevation at the time of failure (El.969 m), and adopting an undrained strength ratio of 0.27 and a high water table, the calculated FS is 1.02.At El.965 m, the FS is 1.04, much less than the design target of 1.3.Based on the back-calculated undrained strength ratio, the design was doomed to fail [my emphasis].”


The breach of the Perimeter Embankment on August 4, 2014 was caused by shear failure of dam foundation materials when the loading imposed by the dam exceeded the capacity of these materials to sustain it. The failure occurred rapidly and without precursors.

Direct evidence of this failure mechanism is provided by an identified shear surface in surviving remnants of the dam core and by deformations consistent with shearing in a weaker glacially-deposited layer of silt and clay about 8–10 metres (m) below the original ground surface. This layer, its properties, and its extent received intense scrutiny during this investigation, and analyses using representative parameters provide indirect evidence that further supports this failure mechanism.

Deposited in a complex geologic environment, the weaker glaciolacustrine layer was localized to the breach area. It went undetected, in part because the subsurface investigations were not tailored to the degree of this complexity. But neither was it ever targeted for investigation because the nature of its strength behaviour was not appreciated.

Throughout, the design investigations took note of the stiff, dense character of foundation soils and used corresponding strength properties in stability analyses. But it was not recognized that this character would change, with a corresponding change in strength behaviour under the increased loading as the dam grew higher. Specifically, it was never recognized that the glaciolacustrine soils that were initially overconsolidated would become normally consolidated, requiring undrained shear strengths for stability analyses. This is the process that affected the weaker glaciolacustrine layer in the breach area that was not accounted for in the design of the dam.

Adding to the antecedent foundation conditions was the unprecedented steepness of the 1.3H:1V Perimeter Embankment slope. This was justified by design analyses without questioning its reasonableness. The higher Main Embankment had glaciolacustrine foundation soils with properties broadly comparable to those at the breach section. But here, the steep slopes were effectively flattened by the addition of a buttress, which explains why the failure did not occur at the highest part of the dam.”

Official Investigation 2: Ministry of Energy and Mines
Summary of Opinion in Support of CIM Investigation
August 24, 2015
http://mssi.nrs.gov.bc.ca/1_CIMMountPolley/Appendix3.pdf (and go to: Conclusions)

Knight Piésold’s Complicity in the Mt Polley Disaster: Media Appendices

News & other snippets summarizing the results of the mt polley Independent Review Panel, showing consensus in the interpretation that the original design of the TSF (by Knight Piésold) failed to take into account the nature of the foundations, and that this was the root cause of the disaster of August 4, 2014.

Media Source 1: Rosemont Mine Truth
Rosemont subcontractor cited for design failures at Mount Polley dam collapse
February 4, 2015

Knight Piésold, Ltd., the engineering firm that designed the Mount Polley mine tailings dam that collapsed last August in British Columbia, failed to properly analyze the strength of the dam’s foundation when it designed the tailings facility, a provincial-sponsored report released Friday concludes.


The Independent Expert Engineering Investigation and Review Panel Report on the Mount Polley Tailings Storage Facility Breach “concluded that the dominant contribution to the failure resides in the design,” according to a media briefing.

Knight Piésold’s design did not account for the presence of a glacial lake deposit beneath the tailings dam foundation, the Vancouver Sun reported.

Knight Piésold has not responded to numerous calls from the media seeking comment, nor has the company posted anything on its website as of Tuesday. The company issued a statement four days after the Aug. 4 collapse of the Mount Polley dam stating that it had turned over all responsibility for the dam in 2011 to AMEC Earth and Environmental.


In Canada, Reuters is reporting the British Columbia government probe found that the breach at Imperial Metal’s Mount Polley mine, which sent billions of gallons of wastewater and sludge into waterways, happened because the dam’s weight was too much for the foundation to bear.

The design did not take into account the complexity of the sub-glacial and pre-glacial geological environment associated with the perimeter embankment foundation,” the panel’s chair, Norbert Morgenstern, said after the 5-1/2-month investigation.

Morgenstern said design flaws created a “loaded gun” and the construction of the steep dam perimeter embankment slopes “pulled the trigger.”

A second report from B.C.’s chief inspector of mines will look at who should take the blame for the massive breach, but Jack Caldwell, a leading North American expert in the field of tailings dams, told the CBC that it’s clear that key questions remain unanswered.

Caldwell, who has more than 40 years’ experience, questions why the tailings pond was built atop unstable ground in the first place [my emphasis] — and indicated a perfect storm of little problems led to the massive breach at Mount Polley.

The Toronto Globe and Mail posted a timeline of key actions at Mount Polley that shows engineers knew the tailings dam was being constructed in an area where unstable post-glacial soils were present. Knight Piésold stated the softer deposits were isolated and would not affect dam stability.

Media Source 2: Mining.com
Failure Resides in the Design: Mt Polley Review Panel
January 30, 2015

Mount Polley’s tailing dam failed because of design failures, wrote the government appointed panel that released its findings today.

The panel said that “. . . there was no evidence that the failure was due to human intervention or overtopping of the perimeter embankments and that piping and cracking, which is often the cause of the failure of earth dams, was not the cause of the breach.”

Rather it was design failures that were the main cause:

The breach of the Perimeter Embankment on August 4, 2014 was caused by shear failure of dam foundation materials when the loading imposed by the dam exceeded the capacity of these materials to sustain it. […]

Deposited in a complex geologic environment, the weaker glaciolacustrine layer was localized to the breach area. It went undetected, in part because the subsurface investigations were not tailored to the degree of this complexity. But neither was it ever targeted for investigation because the nature of its strength behaviour was not appreciated.”
(quoted from the Independent Review Panel)


Media Source 3: The Globe and Mail
B.C. conservation officers raid two sites in Mount Polley investigation
February 4, 2015

The report, released last Friday, found the design of the tailings pond dam failed to address the unstable foundation on which it sat, a flaw that was compounded over the many years the dam was repeatedly raised.


Ms. Louie [of the Williams Lake Indian Band] said the spill has raised concerns about a nearby spawning creek and future salmon runs. Given the size of the spill, and the foundational issues identified in the report, she said it was difficult to imagine the mine reopening.

The tailings storage facility sits on a glacial underground, like a stream. So who’s to say whether or not it will occur again,” she said.


The province has said it will require all operating mines with tailings facilities to provide a letter by the end of June that confirms their foundation is sound. It has said it will also require operating mines with tailings facilities to establish independent tailings dam review boards.

Media Source 3 (b): The Globe and Mail
Timeline from report, of events that lead to Mount Polley Breach
January 30, 2015


Glaciolacustrine (GLU) fine sands, silts, and clays were observed in the main embankment foundation and established to be steady under pressure during the construction. (The embankment was one of three that made up the dam.)


Construction on the main embankment differed from the original design, and configurations were not in accordance with the stability analysis of the original design.


Each of the three dam embankments were to be constructed with a different material, but the Mount Polley Mining Corporation requested approval to use rockfill in all of them.

2001 to 2005

Mine operations were suspended for economic reasons


Renewed construction prompted questions from the Ministry of Energy and Mines about the effects of softer GLU foundation materials downstream on dam stability. Engineering consultant Knight Piésold confirmed the GLU deposits were isolated and would not affect dam stability.


A slope was placed at a steeper inclination than planned because of a delay in the delivery of construction material. A plan to rectify the steep slopes was never carried out.


Complications slowed the raising process. The main embankment buttress was not constructed as designed, turning out to be five metres below its design height and short of its design extent. A strength analysis was performed, and Knight Piésold concluded the embankment would remain stable. A tension crack appeared in 2010.


The 2011 geotechnical site investigation concluded GLU was not of concern.


Reducing the steep slope was deferred until the completion of the entire dam. The 2011 investigation showed the GLU went deeper than previously thought, but stability tests in 2012 did not take the material into account in all three embankments.


During the next months, water continued to rise in the dam. For years, the company managed to stay one step ahead of it by raising the dam, but on May 24, 2014, a small amount overflowed. The breach happened before a plan to add a new buttress to the perimeter embankment could be completed.

Media Source 3 (c): The Globe and Mail
Mt Polley Spill Taints Alaska-BC Mine Relations
February 1, 2015


The report, by an independent panel of geotechnical experts appointed by the B.C. government, found the tailings dam at Mount Polley collapsed because it had been built on a foundation that contained a layer of glacial till (fine sediment deposited by a glacier), which hadn’t been accounted for in the original engineering plan. As the dam grew higher to contain a growing amount of mine sludge, it increased pressure on the foundation until, after 18 years of safe operation, it suddenly gave way, releasing a flood of 10 million cubic metres of water and 4.5 million cubic metres of fine sand [tailings].

Media Source 4: Professional Engineers an Geoscientists of BC
Mt Polley Geotechnical Report Released
January 30, 2015

The panel concluded that evidence indicates the breach was the result of a failure in the foundation of the embankment, a failure that occurred in a glaciolacustrine (GLU) layer of the embankment’s foundation.


The recommendation addressing professional practice states: “Encourage the Association of Professional Engineers and Geoscientists of BC (APEGBC) to develop guidelines that would lead to improved site characteristics for tailings dams with respect to the geological, geomorphological, hydrogeological, and possible seismotectonic characteristics.”

Media Source 5: CBC News, British Columbia
Independent investigation finds foundation of earthen dam failed because of unstable underlying layers
January 30, 2015

An independent investigation has determined the breach of the Mount Polley mine tailings dam in B.C. was caused by a failure to detect a weak layer in its foundation, likening the massive embankment to a “loaded gun.”

The report, which was released on Friday morning in Victoria, said the design failed to take into account the complexity of the instability of underlying glacial and pre-glacial layers under the retaining wall.

The Mount Polley crisis was a long time coming. A report on a breach last year of the tailings dam at the Mount Polley mine said the dam had raised incrementally to meet the requirements for upcoming years. A lack of long-term planning eventually contributed to a catastrophic dam failure, the report said.

Media Source 6: Reuters
Jan 30, 2014
Canada investigation finds flawed design led to mine dam spill

A massive spill from a dam containing mine waste in British Columbia last year was caused by a flawed design for the embankment, which did not account for the presence of a glacial lake deposit at the foundation, an independent panel said on Friday.

The probe found that the breach at Imperial Metal’s Mount Polley mine, which sent billions of gallons of wastewater and sludge into waterways, happened because the dam’s weight was too much for the foundation to bear.

“We concluded the dominant contribution to the failure resides in the design,” the panel’s chair, Norbert Morgenstern, said after the 5-1/2-month investigation.

“The design did not take into account the complexity of the sub-glacial and pre-glacial geological environment associated with the perimeter embankment foundation.”

The panel, appointed by the provincial government with the backing of two Aboriginal bands from the Mount Polley area, also found the collapse was triggered by the construction of a downstream rockfill zone at an overly steep slope.

…And on the lack of anyone being held to account:

Media Source 7: Desmog Canada
No Fines, No Charges Laid for the Mt Polley Mine Disaster
December 18, 2015


How can so many things be done so poorly, sloppily or haphazardly and result in massive damage without someone being ‘at fault?” Ugo Lapoint, Canadian program manager with MiningWatch Canada, stated in a press release. […] ‘This was not an Act of God.’


In sum, two major investigations identify foundational failure as the root cause of the Mt Polley disaster. Knight Piésold designed and oversaw the construction and first 20 years’ use of 4-square kilometre ‘pond’ for tailings storage, despite the location being inappropriate due to (a) pre-existing geology, namely the presence of soft glacial till or glaciolacustrine beneath the perimeter embankment, and (b) the human importance and ecological sensitivity of downstream catchments and corridors.

It is my understanding and belief that KP was negligent in (at least) the following ways:

1. Developing a tailing storage facility upstream of precious freshwater sources and habitats, including Hazeltine Creek, Quesnel Lake, Quesnel River, and the Fraser River. Together these systems – now polluted for the foreseeable future – comprise on of the most important salmon runs in North America, upon which indigenous people have survived and thrived for millennia, and continue to depend upon to this day. For a summary of the salmon’s importance to the affected areas, see the following article in the Globe and Mail of September 14, 2014: http://www.theglobeandmail.com/news/british-columbia/mount-polley-tailings-spill-effects-could-last-for-decades/article20596892/

2. Failing to properly assess the layer of glaciolacustrine in the foundations, to establish its depth and strength characteristics, and to acknowledge that it would indeed compromise dam stability. Specifically, KP failed to: (a) drill deep enough for samples, (b) use proper drilling method for foundation investigations, (c) record the results of all laboratory testing of geological samples from around the perimeter (d) understand that the upper GLU layer would be subject to failure when compressed (see: MEM Report, p. 20-21, 43-45, 139).

3. Failing to illuminate crucial, albeit piecemeal information, concerning the possible weakness of the foundations to the subsequent engineers on record, who proceeded to (recklessly) raise the embankment on the assumption that foundations were stable (MEM Report, p. 20-21,159).

Questions remain: To what extent was Knight Piésold truly unaware of the nature, depth and significance of the glacial till within the foundations? And to what extent was their negligence wilful? In other words, did KP choose not to disclose, or act on known danger, for the sake of maintaining the profitability of the facility, and/or pleading ignorance after the fact? Why did they really begin withdrawing from the project in 2010?

It is foolish of the NSW government to have entrusted a vital freshwater system to the designs of this consultant and the mining company that retains them. And is shameful that the Dargues proponent offers them business as usual, without regard for their unpaid complicity in possibly the worst environmental disaster in the history of British Columbia. However, we must not lose sight of the bigger picture: that no mine or tailings storage facility belongs upstream of riverside communities, municipal pumping stations, national parkland, sensitive aquatic ecosystems, small-scale organic agricultural projects and tourism-dependent economies. All of which can be found along the riparian corridor of the Deua River and its tributaries.

[Afterword: Knight Piesold also designed the Aural S.A. Tailings Storage Facility (attached to a gold mine) in Baia Mare, Romania, which failed in 2000. An embankment failure sent cyanide-laced effluent into the Upper Tiza (a tributary of the Danube), devastaing the ecosystem and contaminating the water supply of some 2.5 million people. The mine was principally owned by Esmerelda Explorations (of Australia). For a concise but heartbreaking description of that event, see Death of a River (BBC, 2000). For a detailed analysis of the cause, see Report of the International Task Force for Assessing the Baia Mare Accident, which concludes that the collapse was caused: “Firstly, by the use of an inappropriate design of the TMF [tailings management facility]; Secondly, by the acceptance of that design by the permitting authorities; and Thirdly, by inadequate monitoring and dam construction, operation and maintenance.” (p.10).

Another of Knight Piesold’s designs was the Omai Talings Dam (also attached to a gold mine) in Guyana, on the Northeast Coast of South America. The Omai facility discharged cyanide-contaminated water into the Omai & Essequebo Rivers in 1995. This resulted in significant wildlife kills in the riparian corridor (the numbers are contested), and human health impacts via drinking water. The Guyan government declared the affected catchment an environmental disaster zone. Eyewitness reports here. Rather than a breach of embankment wall, the Omai spill was caused by internal ‘piping and cracking’ of the core, which allowed contaminated water to escape while leaving the bulk of tailings material inside the TSF. According to the Preliminary Report on Technical Causation for the Omai Tailings Dam Failure (1995), “There are believed to be two primary physical defects in the dam that allowed this process [of piping and cracking] to occur […] Both were produced by known or suspected deficiencies in design, construction, or construction inspection, either singularly or in combination,” (part 3.2: proximate causes of failure). The Final Report is presented as an e-book and requires you to log in.

In 2006, charges against Knight Piesold & other companies associated with the Omai Gold Mine were finally dismissed by the Guyan Supreme Court. The plaintiffs (local Guyans seeking damages) were ordered to pay the companies’ legal expenses. Champagne all round.


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