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Tailings failure case studies, statistics and failure modes (and maybe how to prevent failures) 11 October 2018
Outline › › › ›
Definitions (quickly*) Recent Tailings Dam Failures Statistics of Failure Failure Modes (quickly*) › Detailed examples › Introduction to Tailings Dam Safety Management Systems (if time*) › Risk Management › Summary
Speaker Introduction Vice-President of Geoscience & Materials Testing Past President of the Canadian Dam Association (6 years on Board) Expertise › 16 years of experience in diversified geotechnical projects related to the environmentally sustainable design, permitting, operation and closure of waste storage facilities for mining tailings, landfills, and industrial waste. Mr. LePoudre also has an additional 10 years of experience in construction, sales and finance industries › Expert in the development of Dam Safety Management Systems; including surveillance programs, Dam Safety Reviews and risk management for several operations › Designer of record for waste projects and functions as an EOR for tailings areas › Former partner of MDH Engineered Solutions Education D. Chad LePoudre, P.Eng.
› B.Sc. Civil Engineering (Geotechnical) – 2003 › Graduate studies University of Saskatchewan
Disclaimers › I’m not trying to sell you anything; › except perhaps the need for overall enhanced tailings safety management › All opinions expressed in the presentation are my own › Publically available references are provided throughout › Presentation is not meant as ‘fear-mongering’ or anti-mining, but information sharing and advocating for enhanced mining dam safety by presenting learnings from failures › Short version of presentation – time constraints
Definitions: Dam CDA Definition: A barrier constructed for the purpose of storing water or water containing any other substance, e.g. oil sand tailings, coal waste. The structure should be at least 2.5 meters high and have at least 30,000 m3 or more in reservoir capacity. Alberta Environment & Parks: “or unacceptable consequences to public and environment if failed� - A CFL football field 12ft deep
Hoover Dam
Definition of Tailings Tailings (also called mine dumps, culm dumps, slimes, tails, refuse, process residue, leach residue or slickens): are the materials and liquids left over after the process of separating the valuable fraction from the uneconomic fraction (gangue) of an ore.
dump Dyke
Water cap
Fine tailings
Dyke
*schematic not representative of all facilities
Several thousand million tonnes of mining waste is produced each year (Jakubick, McKenna et al. 2003).
Mining Dam / Dykes From CDA Mining Dams Bulletin (2014): “Retaining structures that exist at mine sites that are designed to retain solids and/or contaminated liquids.�
Definitions: Dyke Raises › Upstream Construction › New lifts over soft tailings Tailings
› Most economic › Up to 1:4 fill ratio compared to downstream
› Downstream Construction › New lifts ‘downstream’ Tailings
› Most geotechnically stable › Up to 4:1 fill ratio compared to upstream › Restrictions often present (i.e. roads, utilities)
› Centreline Construction › New lifts follow centreline of dyke Tailings
› Compromise between upstream and downstream ?
Definitions: Design Life › Design Life › Short Term – temporary › Medium term - operational › Long-term – decommissioning/closure
Closure may be the longest component of the mine life cycle
*CDA Mining Dams Bulletin
Tailings – Pause: Something to Consider › Typical Ore Grades › Gold: 5-16g/t (5:1,000,000), therefore tailings is 999,995g/t › Copper: 0.5-2% (0.5:100), tailings is 995,000g/t › Oil Sands Deposit: 7-14% bitumen › Potash: 15-25% K20 (23-39% KCl)
› Ore generates money › Companies focused on maximizing value
› Tailings consumes money › Sometimes difficult to recognize value of better engineering technologies, although better now than ever › Recent failures have demonstrated potential costs and liabilities
Key Point Mining Companies are more accurately Waste Management Companies
Failure Examples, Statistics and Failure Modes “For any engineer to judge a dam stable for the long-term simply because it has been apparently stable for a long period of time is, without any other substantiation, a potentially catastrophic error in judgment" (Szymanski and Davies(2004): "Tailings Dams - Design Criteria and Safety Evaluations at Closure" - BC Reclamation symposium)
Small changes over time are difficult to notice
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Tracking Failure › Several organizations attempted/attempting to compile tailings failure data, for example: › WISE Uranium Project: http://www.wise-uranium.org/mdaf.html › Canadian Dam Association (CDA) Mining Dams Committee: www.cda.ca › International Commission of Large Dams (ICOLD): http://www.icold-cigb.net/ › Recent: https://worldminetailingsfailures.org/
›Many publications, reports, news headlines › Mining Watch Canada › Linsday Newland Bowker › Shahid Azam (University of Regina): http://www.infomine.com/library/publications/docs/azam2010.pdf
Tracking Failure
https://worldminetailingsfailures.org/
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http://www.wise-uranium.org/mdaf.html
Recent Examples of Tailings Failures Cieneguita Mine, Mexico
› June 4, 2018 › 7 deaths (missing) › Tailings ran through 26 kilometers along the Cañitas creek in the proximity of the mine › 249,000m3 of tailings and 190,000m3 of construction materials. › No information on route cause found, although appears that dam was under construction
https://born2invest.com/articles/cieneguita-mine-accident/ http://www.mining.com/five-bodies-rescued-collapsed-mine-mexico/
“Many are expecting Minera Rio Tinto and Pan American Goldfields to take full responsibility for what happened. For now, both companies have yet to release a clear statement on their next course of action.”
Recent Examples of Tailings Failures Newcrest Cadia Mine, Australia
› March 9, 2018 › No deaths › Slump of interior, upstream dam following a two small seismic events in the days preceding (4.3 magnitude) › Limited Details to date, but appears to be liquefaction flow slide of an upstream constructed tailings dam › No loss of containment › Operations resumed, with tailings placement in pit (but sterilizing significant ore resources)
https://blogs.agu.org/landslideblog/2018/03/12/cadia-1/ http://www.newcrest.com.au/investors/market-releases/cadia-northern-tailings-dam https://www.riskope.com/2018/03/14/tailings-dam-failure-at-the-cadia-ridgeway-mine-in-australia/
Recent Examples of Tailings Failures Mishor Rotem,Israel
› June 30, 2017 › No deaths
http://blogs.agu.org/landslideblog/2017/07/07/mishor-rotem-1/
› “Toxic wastewater that surged through a dry riverbed in southern Israel at the weekend left a wake of ecological destruction more than 20 km (12 miles) long. The flood began last Friday when the 60 meter (yard) high wall of a reservoir at a phosphate factory partially collapsed, letting loose 100,000 cubic meters (26.4 million gallons) of highly acidic wastewater in the Ashalim riverbed.”
Recent Examples of Tailings Failures Tonglvshan Mine, China
› March 12, 2017 › 2-3 deaths › 200,000m3 › No photos available › Original News Article appears to have been removed
http://webcache.googleusercontent.com/search?q=cache:7kud9wnAcA8J:www.asianmetal.com/news/data/1341807/Hubei% 2520Tonglvshan%2520Mine%2520of%2520Daye%2520Nonferrous%2520halts%2520opeartion%2520due%2520to%2520dam%2520break&num=1&hl=en&gl=ca&strip=0&vwsrc=0
Recent Examples of Tailings Failures Henan Xiangjiang Wanji, China › August 2016 › Approx. 2 million m3 fine tailings (reported release) › Very little information › Media reports that evacuations were successful › Operations were shut down (est. 3-6mo.)
http://www.mining.com/major-tailings-burst-reported-in-china/
Recent Examples of Tailings Failures Fundao Dam, Samarco, Brazil November 5, 2015
2 weeks later, 400 miles away
Recent Examples of Tailings Failures
Samarco Mine (approx. 300km north of Rio de Janeiro)
Rio de Janeiro
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Recent Examples of Tailings Failures Fundao Dam, Samarco, Brazil › › › › ›
November 5, 2015: ~4:30pm – Samarco Iron Ore, Brazil (BHP Billiton/Vale) 19 deaths – 21 people facing charges for murder (no recent update) Largest Tailings Dam Failure in Recent History ~100m high dam: Estimated at up to 60 million cubic meters Samarco failed after some small earthquakes caused an already stressed tailings dam to liquify, according to the Fundao Tailings Dam Review Panel › Static liquefaction was ‘root-cause’, but many contributing factors › BHP-Billiton CEO has said another similar event would be a “company killer” › ~30% loss in market capitalization › Dam Safety Reviews of all assets across the company › Fines levied by Brazilian Government assessed at similar values as the BP Disaster (~$55 Billion) › ICMM launched ‘global tailings practices’ study
http://www.mining.com/bhp-vales-samarco-reach-final-settlement-brazil-dam-failure/
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Recent Examples of Tailings Failures Mount Polley, BC, Canada
› August 4, 2014 › Approx. 10 million m3 fine tailings (reported release) and 4.5 million m3 water › Expert Panel - now most studied tailings dam in Canada › No deaths – limited environmental impact › Operations were shut down for a year › ~$100million to repair › Root cause: undrained failure of undetected glacial till layer
Recent Examples of Tailings Failures
Source: http://en.wikipedia.org/wiki/Mount_Polley_mine_disaster
Recent Examples of Tailings Failures Mount Polley, BC, Canada No deaths Hazeltine creek reconstructed Environmental Impact Assessment determined low residual impact 3 months after the failure
Recent Examples of Tailings Failures Mount Polley, BC, Canada
1 root cause‌ Many contributing factors that differ from design
Source : Jack Caldwell – Infomine
Recent Examples of Tailings Failures
› Sept 10, 2014 › Herculano, Brazil › 3 deaths
› Aug 5, 2015 › Gold King Mine Spill, Colorado
› Oct 31, 2013 › Obed Mountain Mine, Alberta
Recent Examples of Tailings Failures Black Swan: An event or occurrence that deviates beyond what is normally expected of a situation and is extremely difficult to predict
Maybe not a Black Swan
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October 2010 Kolontar, Hungary 10 deaths, 120-150 injured $632million fine1
› July 1985 › Stava, Italy › 268 deaths
1. http://www.theglobeandmail.com/news/world/hungary-villages-still-rebuilding-one-year-after-toxic-sludge/article595937/
Statistics Major Tailings Dam Failures Many studies, but all partially incomplete › ICOLD, 2001 › 221 failures studied between 1970-2001 › Annually 2 to 5 major tailings dam failures › Estimated ~3,500 tailings dams worldwide (remember this)
Key Point Annual Rate of Failure = ~ 1:700 to 1:1,750 (ICOLD data)
› Knowing these statistics, a couple interesting questions: › What is the life span of your facility? › Per company: › (number of facilities) x (age) ? Full list: http://www.tailings.info/knowledge/accidents.htm Source: ICOLD, Bulletin 121 – “Tailings Dams, Risk of Dangerous Occurrences. Lessons learnt from practical experiences”
2017 ICOLD Presentation by China
2017 ICOLD Presentation by China
Total = 8,869
Statistics Major Tailings Dam Failures #1 – Slope Stability - 47/221 #2 – Earthquake (Seismic) – 34/221 #3 – Overtopping – 30/221 › Also annotated to the graph are dam ‘types’ › Upstream - 95/221 highlighted › Unknown - 50/221 (assumed to be data sensitivity)
Full list: http://www.tailings.info/knowledge/accidents.htm Source: ICOLD, Bulletin 121 – “Tailings Dams, Risk of Dangerous Occurrences. Lessons learnt from practical experiences”
Statistics
“For a world inventory of 18401 mine sites, the failure rate over the last one hundred years is estimated to be 1.2%” 1
~50 events/decade
~20 events/ decade
22 2010s
1. Source: Azam, Li – “Tailings Dam Failures – A review of the last 100 years” Geotechnical News – December 2010
Statistics
Source: Bowker & Chambers – “The Risk, Public Liability & Ecomonmics of Tailings Storage Facility Failures” July 2015
Statistics
2018: https://worldminetailingsfailures.org/
Failure Modes Physical / Structural -
Slope failure Foundation failure Surface Erosion Internal Erosion Seismic
Functional -
Adequate size / Volume Resultant density Beaching angles Dewatering Reclaim quality
Contributing Factors
Environmental -
Groundwater Surface water Dust Noise Visual Impact ‌
Failure Modes Physical / Structural
Slope Failure -
Raising of Dyke Placement of tailings Undercutting Poor construction materials - Over-steepening - Direct loading - Seismic
Foundation Failure -
Undrained loading Sensitivity clays Seepage forces Strength loss Weak layers Liquefaction
Internal Erosion
Surface Erosion -
Overtopping Runoff Excessive inflow Insufficient outflow conveyance - Inadequate rip-rap - Landslide into impoundment
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Piping Lack of adequate filter Zoned dams Sinkholes Unprotected conduits Joints/seepage in foundation/ abutments
Contributing Factors
Failure Modes
Contributing Factors
Design / Construction -
Dam type Materials Hydrology/hydrogeology Construction Outlet Structures Freeboard Foundation/ Abutments Chemical processes Biological Processes
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Operation / Maintenance
External Factors
Rate of deposition Water Management Beach width Inspection / Monitoring Maintenance Chemical processes Biological processes
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Human Activity Adjacent structures Adjacent activities Climate/weather Seismic activity Earth movement Unforeseen
‌a partial list
Potential Dyke Failure/Trigger Mechanisms › Need to determine what the hazards may be to assess likelihood
› Note: Not intended to be an exhaustive list. Each facility will have a unique combination of hazards and failure mechanism
*CDA workshop on Tailings Dam Stability Analysis October 2017
How to prevent tailings dam failures My thoughts: A comprehensive Dam Safety Management System incorporating Risk management and Best practices › Constantly evolving
** An entire course could be spent on this topic **
› Good guidance from organizations › Good regulations/legislation › Qualified people • Competent Responsible Engineer (EOR) • Intelligent ITRB • Engaged Staff • Committed Management • Educated Regulators • Informed Stakeholders
www.infomine.com/library/publications/docs/Howtoavoidfailure.pptx
Dam Safety Management System Two excellent references: - CDA 2007 Dam Safety Guidelines (rev. 2013), and Mining Dams Bulletin (2014) - Mining Association of Canada: Guide to the Management of Tailings Facilites (2017) › Dam Safety Management System › A function of Owner’s policies and priorities, which is a function of Public Policy › Process Driven › Flow Chart of Plan, utilizes Plan, Do, Check, Act philosophy
Dam Safety Management System › CDA and MAC System widely used across Canada and internationally with similar terms and Definitions › Strongly adopted by the Hydro industry previous to ~2005-2010 › Mining industry began adopting similar principles utilizing MAC and CDA guidance › However, these systems represent a process to reconcile pieces of a management system with primary components: › Slope Stability Management › Performance Management › Monitoring and Surveillance › Risk Management
For some older or unsophisticated sites, there’s a lot of work to do!
What does it mean to have “Best” Practices My view:
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- Compliant with Regulations
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- Compliant with MAC and CDA guidance (my advice) ›
- Other recommendations and guidance, as appropriate ›
Silva (2008) – excellent journal paper ›
Silva et.al. (2008) “Probability and Risk of Slope Failure”, Journal of Geotechnical and Geoenvironmental Engineering, ASCE, December 2008
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Summary › Tailings dams continue to fail regularly around the world, resulting in significant consequences, media scrutiny, fines, and even criminal charges › Many potential failure modes exist, but often many contributing factors (despite defined root causes) › A robust, constantly improving Dam Safety Management System is required for the life of a structure (design through closure) › Risk Management is a powerful tool for an Owner › Best (leading) practice is constantly evolving › Tailings dam engineering is a highly specialized field requiring qualified persons (consultants, regulators, review boards, owners representatives) › Closing tip: Beware excess over-confidence (i.e. “it can’t happen here”) “It’s only hubris if I fail” – Julius Caesar
Thank-you Questions, comments, additional info: Chad.LePoudre@snclavalin.com
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