Jack Caldwell, P.E. has a B.Sc. in Civil Engineering, an M.Sc. (Eng.) in Geotechnical Engineering and a post-graduate law degree. He has over 35 years engineering experience on mining, civil, geotechnical and site remediation projects. He has worked on numerous projects throughout southern Africa, Europe, Canada and the United States.
Here are the stories of the seven dam failures that have occurred since the beginning of 2012. Six are failures of tailings facilities. The seventh is a rockfill dam. The following are extracts from technical papers that I wrote well before the Mt Polley failure. Details of the first three are available at this link: Tailings Facility Failures in 2012. Details of the remaining four are in a paper that I will present at the Tailings and Mine Waste 2014 conference in Colorado in October of this year.
There is no common thread, except possibly a failure by those responsible to understand the beast, the Wicked Stepmother, they were dealing with. If you see other common threads, then please comment.
GULLBRIDGE MINE, NEWFOUNDLAND, CANADA
The old Gullbridge mine tailings facility in Newfoundland is the responsibility of local government. Observations indicate potential problems. A respected consulting firm, Stantec, issues a report on the safety of the facility and concludes they cannot tell what is going on because of poor construction records, copious vegetation, and a lack of geotechnical data. They recommend a full investigation. But the local authorities delay, preferring to spend money on inexpensive reports in preference to expensive physical action, do nothing. The dam fails and tailings spill into the downgradient wetland. Now they are fixing the failure.
The Newfoundland and Labrador Department of Environment and Conservation (2012) reported:
“At 7:45 am on Monday December 17, the tailings dam at the former Gullbridge copper mine, central Newfoundland failed while work was under way to stabilize it. The failure resulted in a breach of the 7 m high dam approximately 25 m wide. The dam was impounding mine tailings that were partially covered by water forming a tailings pond. As a result of the failure, the pond drained completely over the next few hours, and a small amount of the tailings escaped. Small quantities of tailings pond water continue to flow from the breach.”
Gullbridge is a typical example of local authorities taking over a tailings facility without making the mine close it or even document how it was built. The local authorities appear not to have had the capacity to manage the facility. They engaged reputable consultants but failed to act on their advice, and appear to have stalled in order to minimize expenditure.
HB MINE, SALMO, BRITISH COLUMBIA, CANADA
The mine closes and very intelligently gets the local authorities to take over the site as a landfill. It appears the landfill folk in the local authorities engineering group did not understand tailings. Environmental groups warn of the dangers, but nobody hears them. It rains a lot, and piping and leaks are observed. In July 2012, the earth dam sloughs; a sinkhole develops; tailings move out into the environment; it will now cost almost a million dollar to fix; and the taxpayer pays.
A little more detail:
“Residents who could be affected by a structural failure impacting the highway and properties below the site have been notified by the RCMP. Currently flaggers are positioned on the highway as a precautionary measure.
Geotechnical engineers have installed three pumps to decrease the level in the tailings pond as a first step. Additional larger diameter pumps and siphoning hoses are en route to continue to reduce water levels. An outlet channel is also being deepened. Several excavators are on site and will work at in-filling areas of seepage when they are able to be deployed safely.
Environmental monitoring and reporting is ongoing and 24 hour security has been implemented at the site. The weather forecast is favorable – with little or no precipitation forecast – and geo-technicians and engineers on site indicate the area is gradually getting drier. This should permit additional remediation planning and on-site work to proceed over the next few days.”
The fact is it is expensive to maintain so-called closed tailings facilities. It takes expertise and experience to look after closed tailings facilities. And even the best consultants are cowed by clients who do not want to spend money, regardless of how dire the situation
CASA BERADI MINE, QUEBEC, CANADA
A news report describes the failure in these words:
“During a routine evening inspection of the tailing ponds on Wednesday, May 1, 2013, at the Casa Berardi Mine, located approximately 95 kilometres north of the town of La Sarre, in the Abitibi region of northwestern Quebec, it was discovered that there was a breach of an internal tailings dyke which resulted in a surge of liquids and suspended solids over the external tailings dyke. A majority of the material was contained inside the tailings pond containment area and no further discharges into the environment have occurred. The Casa Berardi Mine has four tailings containment ponds and the material flowed from one tailings pond into another tailings pond, neither of which are in use for current operations.”
From the little available on the web, it appears the mine was in transition at the time of failure. Hecla had recently bought the property from its previous owners and had not fully taken charge. It is just possible that in the inter-regnum those leaving the mine had not fully passed off operation to those taking over the mine, and this event occurred in the absence of committed oversight.
PHILEX MINE, PHILLIPINES
A tailings pond in the Philippines at Philex Mining Corporation’s Padcal gold mine is discovered to be leaking on August 1, 2012. Philex suspends its operations in order to investigate the source of the leak. The company deploys cleanup crews to remove chemicals and sediments discharging into the river nearby. The tailings failure was said to have been caused by heavy rains. However, I believe the spill resulted from failure of the penstock.
The mine is owned by a Hong Kong mining company and they have done a superb job of controlling the flow of information about what happened. The authorities have fussed and fumed, but to no avail. It seems the penstock is now plugged and mining and tailings disposal continues apace.
This failure also proves that the size and public pronouncements of the mining company are vain hot-air when it comes to the tailings facility. The penstocks had leaked for weeks before the main event; yet nobody did anything. And prior to the event, the government was supine. After the event, the government is grousing, suing, and making noise.
OBED MOUNTAIN COAL MINE, ALBERTA
News reports describe the failure thus:
“On October 31, an impoundment holding a slurry of waste from Sherritt International’s Obed Mountain coal mine failed releasing approximately 670 million litres of waste into the Athabasca River watershed. Alberta government press releases referred to the waste as “process water”, “suspended solids, which include such things as clay and organic matter”, and sediments containing “such things as clay, mud, shale and coal particles”. Official statements have provided very little information about the extent or magnitude of the spill, and a November 4 statement stated the spill was somehow “contained”. As reported in the Edmonton Journal, the only thing that was contained was the waste remaining at the mine site. The plume released to the river ex-tended 113 km by November 8.”
It appears that operations at the mine had been suspended last year, due to what is believed to be overwhelming economic and market pressures. Reclamation was in progress at the time of failure.
One report states “nobody knows when the facility was last inspected.”
Maybe they were just too busy with closure to notice facilities that were open. Once again this failure appears to have occurred at a time when there was a change of staff and operating procedures at the mine. May we conclude that when such changes are in progress, failure probabilities increase?
DUKE ENERGY, NORTH CAROLINA, USA
The first I read of this failure on Feb. 2, 2014 was a report that started:
“Duke Energy said Monday that 50,000 to 82,000 tons of coal ash and up to 27 million gallons of water were released from a pond at its retired power plant in Eden into the Dan River, North Carolina and were still flowing. Duke said a 48-inch stormwater pipe beneath the unlined ash pond broke Sunday afternoon. Water and ash from the 27-acre pond drained into the pipe.”
A second report indicates that they knew of the broken pipe.
“Duke initially estimated up to 82,000 tons of ash spilled from two ponds at a coal-fired plant in Eden that the utility closed two years ago after a stormwater pipe that ran under the ponds ruptured.”
I liked this statement most:
“Duke spokeswoman Paige Sheehan said the utility has hundreds of people working to repair the leak, and the flow of ash into the river has been slowed to a trickle – and shut off completely at times.”
And despaired at this statement;
“It’s not clear why the reinforced concrete pipeline broke. Built in the 1960s, it runs beneath the unlined ash pond – the only one of Duke’s 14 North Carolina ash ponds with such a pipe beneath it. A power plant in Indiana also has a pipe under its ash pond.”
In fact it appears that there was also a 36-inch diameter pipe beneath the pond. I could not establish if it too failed.
Clearly there should not be pipes, in particular old ones, beneath tailings facilities. I believe this is true of stormwater pipes and penstock pipes. Also we may conclude that when politicians intervene to protect companies from regulators, failure will occur sooner or later,
A recent report on cleanup reads:
“The biggest ash deposit yet found in the Dan, following a Feb. 2, 2014 spill 25 miles upriver at Duke Energy’s Dan River power plant, lies on the bottom just above Danville’s water in-take. The ash covers an area about 300 yards long and 25 yards wide. It is up to 1 foot deep. Its removal from the river will be far harder than its release into it from a broken metal pipe. Duke’s contractor will use a dredge that vacuums ash off the river bottom while disturbing sediment as little as possible. About 2,500 tons of ash and sediment will be sucked up by the end of June — a small fraction of the up to 39,000 tons that spilled.”
TOKWE MUKOSI, ZIMBABWE, AFRICA
Although not a tailings facility, the story of the Tokwe Mukosi dam hold lessons for the tailings industry. Zimbabwe is a dry land. Water is precious. Yet land is valuable for the subsistence farmers. Decades ago the authorities decided to build a dam in southern Zimbabwe to provide more water for agriculture.
Coyne and Bellier, a famous French dam design and construction company recommended a concrete arch dam. The Zimbabwean Department of Water Development said this would be too expensive. They decided to use their own design: a rockfill dam with an upstream concrete facing.
As is so often the case in Africa, construction started, was delayed, was undertaken intermittently, and funding was sporadic and/or diverted. An Italian company was brought in to do construction. Nobody living in the zone of future dam inundation was moved.
The rockfill embankment was planned to rise to 89-m high and impound 1.8 billion liters of water.
Placement of the rockfill proceeded over a decade or so. Then last year it rained. Reportedly the rainfall was about twice the annual average, although nobody seems to know for sure. The water started to flood the reservoir. People moved away fast. Heavy flooding in February 2014 caused a failure on 4 February, 2014.
Because the upstream concrete facing was not in place, water seeped and ultimately flowed through the rockfill. The authorities assured everyone: “The dam is sound; it is not failing; it is only water squeezing through the rocks.” Although wiser council prevailed and those living downstream of the dam were evacuated. This in spite of the following assurances by Engineer Mairukira, who said:
- The dam wall is premised on similar ones in other countries
- The structure is strong and will never collapse
- The dam wall is structurally safe
- We are using the latest technology to build it.
Pictures show a significant slumping of the rockfill of the front face of the dam. It still amazes me that the dam did not slump and fail completely. The Italian contractors continued to build up the crest of the embankment to keep ahead of the rising waters. Their courage, or folly, is astounding.
For the original source of this column, click here: http://ithinkmining.com/2014/08/12/mt-polley-snow-white-and-the-seven-dwarfs/