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By Shane Lasley
Mining News 

Verdict is in on Mt. Polley dam

Panel finds glacial deposits in foundation failed to support structure; questions linger about pending dams upstream from Alaska

 

Last updated 2/8/2015 at Noon



A design flaw resulting from an inadequate understanding of the glacial lake sediments that formed a portion of the foundation on which the tailings dam at the Mount Polley mine located in south-central British Columbia was built caused the structure to collapse under its own weight, according to engineers tasked with finding out why the dam burst on Aug. 4. Mount Polley is an open pit copper-gold mine with a developing underground project.

"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 (glaciolacustrine, or glacial lake deposit) layer in the vicinity of the breach and to recognize that it was susceptible to undrained failure when subject to the stresses associated with the embankment," according to a Jan. 30 report released by the government-appointed panel.

Simply put, the layer of glacial lake deposits could not hold the increasing weight of the growing dam, at least the way the dam was being built. Likening the GLU layer to a loaded gun, the engineers said the extreme steepness of the dam's downstream slope pulled the trigger.

Alaskans raise concerns

Though Mount Polley is located in the Cariboo region of south-central British Columbia, many Alaskans who live and work downstream of other mine development projects located in northwestern British Columbia worry that loaded guns may be lurking in designs for their tailings dams; and, if the figurative triggers these flaws are pulled, the effects could spill into salmon-bearing rivers that flow through the Southeast Alaska Panhandle.

Red Chris, a gold-copper project ready to be put into production by Imperial Metals Corp., tops the list of the pending mines situated upstream from Alaska. Imperial also operates the Mount Polley mine.

"A similar accident at a trans-boundary mine like Red Chris could release large quantities of tailings that are more toxic than the Mount Polley spill," said Sitka City and Borough Mayor Mim McConnell. "The Mount Polley disaster was a clear sign that B.C. cannot assure us trans-boundary waters and fish won't be polluted by the province's aggressive mining agenda."

Other advanced B.C. exploration or development projects located in the region upstream of Southeast Alaska include Kerr-Sulphurets-Mitchell (Seabridge Gold Inc.), Tulsequah Chief (Chieftain Metals Corp.), Brucejack (Pretium Resources Inc.), Schaft Creek (Copper Fox Metals Inc.-Teck Resources Ltd.), Galore Creek (Novagold Resources Inc.-Teck Resources Ltd.) and Kisault (Avanti Mining Inc.)

Red Chris gets green light

Following the Mount Polley spill, Imperial Metals' Red Chris project has been the target of extra scrutiny by local First Nations as well as Alaskans living downstream of the pending copper-gold mine.

Before giving a final okay to begin operations, the local Tahltan First Nation chose the award-winning engineering firm Klohn Crippen Berger to complete an independent review of the Red Chris tailings facility.

During their site inspection, Klohn Crippen Berger engineers found the "North Starter Dam" to be appropriately designed and a visual inspection showed none of the telltale signs of instability.

Though engineers were unable to inspect the yet-to-be constructed permanent dams, they said the general designs being considered for these pending facilities are sound.

Klohn Crippen Berger, however, raised concerns about the potential of water seeping through soils at the base of the tailings facility, which could cause stability issues.

This permeability issue was taken into account during the original dam design, and it was determined that the very fine material in the tailings themselves would seal the more permeable natural material and prevent seepage.

All told, the engineering firm listed 22 recommendations for the safe construction and operation of the tailings facility at Red Chris. Most of the suggestions in the report are associated with risk mitigation through diligent monitoring of potential risks; keeping seepage and other models updated based on observations; and finalizing emergency preparation and response plans.

Of these recommendations, the last one on the list seems to be the one that requires the most immediate attention and would likely be the cornerstone of the other 21 suggestions in the report.

"We strongly consider that the Red Chris site appoints a technical review board immediately that consists of senior, independent engineers and scientists in the following technical areas: geotechnical and tailings engineering, hydrology, hydrogeology and geochemistry-water quality," the engineering firm suggested. "Good practice is to have a management system in place that plans tailings disposal and executes tailings disposal, (and) raises, monitors and improves the performance of the system."

Imperial Metals and the Tahltan Nation are implementing a plan to ensure that the tailings facility recommendations are addressed.

In a Jan. 26 production update, Imperial Metals reported that commissioning at Red Chris is underway. The company expects to fire up the mill by early February and begin production at the gold-copper mine shortly thereafter.

KSM review board

Seabridge Gold's Kerr-Sulphurets-Mitchell copper-gold project, which is located on a salmon-bearing river that flows into Alaska near Ketchikan, is another northwestern B.C. mine proposal of concern to people in Southeast Alaska.

According to a prefeasibility study completed in 2012, a 130,000-metric-ton-per-day mine at the project better known as KSM would produce an estimated 850,000 ounces of gold and 195 million pounds of copper over a mine life anticipated to last more than five decades.

In July, KSM acquired the provincial approvals it needs for development, but federal authorization by the Canadian Environmental Assessment Agency is pending.

To ease worries on both sides of the border, Seabridge Gold Jan. 26 reported the establishment of an independent geotechnical review board charged with ensuring KSM's water and tailings dams are properly built and managed.

Seabridge says this eight-person panel will have unimpeded access to all technical data necessary to enable them to assess the tailings facility and water dam at KSM on an ongoing basis to ensure that these structures meet internationally accepted standards and practices.

The four core members of the review board are Andrew Robertson, a co-founder of SRK Consulting; Gabriel Fernandez, an award winning civil engineer; Terry Eldridge, a principal of Golder Associates; and Anthony Rattue, a director for Québec of the Canadian Dam Association and member of that organization's dam safety committee.

Four support members, which each provide the panel with 35-40 years of experience in hydrogeology, civil engineering, geotechnical engineering and soil mechanics, are available to lend their individual expertise to the board as needed.

"The establishment of the IGRB is a voluntary undertaking on our part to ensure that KSM's tailings management facility and water storage dam are constructed, operated and decommissioned in keeping with the best practices in the industry," explains Seabridge Gold Chairman and CEO Rudi Fronk. "The team we have assembled includes some of the leading experts globally in their field and we are honored that they have agreed to serve in this important role for the KSM project."

More oversight

Following the findings of the independent panel that investigated the Mount Polley dam failure, the B.C. Ministry of Energy and Mines said that it will require all British Columbia mines with tailings storage facilities to establish independent review boards similar to the one proactively assembled by Seabridge.

The provincial government is also requiring that all existing mining operations in B.C. find out if materials similar to those responsible for the dam failure at Mount Polley exist below their respective tailings facilities and, if they do exist, whether the materials are fully understood and the dams were designed to account for the foundational conditions. A report on these findings is due to the Ministry of Energy and Mines by the end of June.

Despite these steps by the province, some Southeast Alaskans are calling for stronger oversight by state and federal officials, including involvement by the International Joint Commission, an organization formed in 1909 to deal with U.S-Canada trans-boundary water issues.

"We have the right to be consulted on actions that could harm our culture and livelihoods, even if those actions are happening in Canada. This is why we need the State of Alaska and the (U.S.) State Department to do all they can to defend our way of life in the face of these threats," Rob Sanderson Jr., co-chair of the United Tribal Transboundary Mining Work Group.

The Juneau City and Borough Assembly Feb. 2 passed a resolution calling for International Joint Commission involvement in the potential northwestern British Columbia mines, making Alaska's capital city the latest in a growing number of Southeast Alaska communities asking for this higher oversight.

Juneau Mayor Merrill Sanford told KTOO public radio in Juneau that the assembly doesn't want to stop mining in neighboring B.C., just a stronger scientific look at potential downstream ramifications of such development.

B.C. Minister of Mines Bill Bennett believes trans-boundary concerns are best addressed on the state-provincial level.

"I think that if the federal governments have to get involved - for example, through the International Joint Commission - it is almost too late," the B.C. mines minister told Alaskans in November.

"It is my intention to work really closely with Alaska to make sure we can manage our trans-boundary issues - British Columbia and Alaska," he added.

 

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