brazil's mining tragedy : lessons for the mining industry
Post on 16-Feb-2017
Embed Size (px)
Page 1 of 7
Brazil's Mining Tragedy : Lessons for Indian Miners Prabhash Gokarn, Pankaj Satija, Dipak Behera, Tata Steel
Abstract The Brazilian mining tragedy was an eye-opener for the mining fraternity to introspect on the existing tailing management processes, identify gaps, complete hazard identification and risk assessments, and modify or develop safe operating procedures and emergency preparedness plans in line with the guidelines issued by Statutory Authorities from time to time. This is necessary to avert the occurrence of similar incidents in the future. INTRODUCTION
Samarco Mineração S.A. is a Brazilian mining company founded in 1977. It is currently a joint-venture between Vale and BHP Billiton, each holding 50% of the company's stocks. BHP Billiton is the world's largest mining company, headquartered in Australia. Vale, which is headquartered in Brazil, is the third-largest mining company in the world and is also the largest producer of iron ore and iron ore pellets, producing over 350 million tonnes of iron ore and pellets annually. Vale produces over 60% of all the iron ore produced in Brazil and around 15% of all the iron ore in the world.
Fig-1a : Location of Bento Rodrigues Fig-1b : Mariana mining site Samarco’s mines, located in the Minas Gerais province of in south-eastern Brazil, at Mariana (Germano mine) and Ouro Preto (Alegria complex), produces iron ore pellets post a gravity concentration & beneficiation process. Samarco produces ~ 24 million tons of ore concentrate and ~21.6 million tons of pellets annually. The tailings are stored in four tailing dams that surround the mines.
Disclaimer: This paper is an amalgamation of author’s own views and thoughts. Tata Steel Limited does not necessarily subscribe to the views and thoughts expressed here and should not be held responsible for the same.
Bento Rodrigues Mariana mining site
Page 2 of 7
THE INCIDENT Between late afternoon and evening of 5 November 2015, two tailing dams in Mariana collapsed. The tailing dams which stored tailings and water, suffered a sudden break-out – catastrophic flow side failures - leading to release of over 60 million cubic metres of sludge and mining waste and flattening nearby towns in the state of Minas Gerais.
Fig 2 : Sludge and mining waste flows through Bento Rodrigues
SEQUENCE OF EVENTS At approximately 3:30 pm on the afternoon of 5 November, the Fundão dam presented a leak. Immediately, a team of outsourced employees was sent to the scene. They tried to mitigate the leak by deflating a part of the reservoir. The Fundão dam broke, releasing tailings into the Santarém dam. Around 4:20 pm a rupture occurred in the Santarém dam as well, releasing a large volume of toxic sludge into the Santarém river valley; and Bento Rodrigues, which lies in the valley below, was almost entirely flooded by the cascade of mud that ensued after the disaster at the dam. Other villages and districts that are located in the Gualaxo river valley, also in the region of Mariana, suffered minor damage. The flooding made Bento Rodrigues completely inaccessible by road, which hindered fire-fighters' access to the rescue. The only option for transport into or out of the location was via helicopter. Around 600 people were evacuated to the nearby town.
Page 3 of 7
Fig 3: Bento Rodrigues inundated by Tailing Waste Fig 4: 600 people were evacuated by helicopter
IMMEDIATE IMPACT The accident caused at least 13 casualties with 19 people reported missing and injured 16 people. The 60 million cubic meters of iron waste contaminated the Doce River and its tributary, Rio Gualaxo do Norte, and the toxic brown mudflows reached the Atlantic Ocean 17 days later.
Fig 5(a), (b): Toxic mud from the river contaminating the Atlantic Ocean
On 9 November, the city of Governador Valadares stopped all water intake due to the mud on the Rio Doce. The next day, a State of Public Calamity was decreed in response to the water shortage in the city. LONG TERM IMPACT
The river basin has a drainage area of about 86,715 square kilometres, and covers 230 municipalities that use it for subsistence. According to analyses carried out in the city, the mud contains greater than acceptable concentrations of heavy metals - arsenic, zinc, copper and mercury which is now present in the Rio Doce, make the water un-useable for human consumption.
Already, the lack of oxygen and high temperatures caused by the pollutants has killed much of the aquatic life along a 500km stretch of the river. Thousands of hectares of protected areas have been destroyed and there is a total extinction of all the biodiversity along this stretch of the river.
On 22 November, the waste reached the Atlantic Ocean. The toxic mud is spreading across the Espírito Santo coast, where cities closed down access to beaches. The mud plume is expected to disperse along the coast around six miles south of Regência, two miles north and 1.5 miles out to sea.
Page 4 of 7
Fig 6 - The Espírito Santo coast before the tragedy
Fig 7 - The toxic mud is spreading across the Espírito Santo coast
The area is rich in marine life, including humpback whales, the La Plata dolphins, and the endangered leatherback turtle. The beach is one of the only regular nesting grounds for the leatherback turtle in Brazil.
Fig 8 – Ecological Impact on the Espírito Santo coast
According to biologist and ecologist Andrew Ruschi, who studies marine biology at the Estação Biologia Marinha Augusto Ruschi in Santa Cruz, Espírito Santo, the waste will take at least 100 years to dilute to levels anywhere near previous levels.
Page 5 of 7
ECONOMIC IMPACT Brazilian President Dilma Rousseff announced a fine of $66 million against Samarco immediately after the incident. The company also faces a $ 265 million liability for the clean-up. On 28th Nov, the Brazilian government announced it will sue mining giants BHP Billiton and Vale for $US5.2bn. This financial Impact of Brazil Dam Catastrophe weighs heavily on both Vale and BHP Billiton. BHP’s stock price fell to its lowest level in seven years, with a similar impact on Vale.
Fig 9 - Brazilian President Dilma Rousseff in an Arial Survey of the region
WHAT WENT WRONG It is amply evident that the tragedy was waiting to happen. Implementation of mining regulations in Brazil is notoriously lax. Vale; which holds 50% stake in the mine; was elected the world’s worst company in January 2012 by the Public Eye People, for its human rights and environment record. The chain of events that led to the disaster is as follows:
1. The state in 2013 allowed Samarco to increase the dam’s height, over-riding concerns raised by a commissioned study by the environmental institute Instituto Pri stino.
2. Recommended monitoring of the dam was lax. Samarco said that it monitored the dam with drones water level gauges, surface marks, bi-weekly and daily checks. However, the checks were obviously not enough as it gave absolutely no advance warning of the impending disaster.
3. There was no contingency plan or a “dam break analysis” done. When the dam broke, no one knew what exactly to do. Thus, people in harm's way were not warned and evacuated in time.
4. Many modern mines use safety techniques such as radar and laser-monitoring which should have warned of any structural problems. However, none of these techniques were adopted at the Samarco mine.
Page 6 of 7
5. The state of Minas Gerais has suffered five dam breaks in the last decade. However, there was no learning from the repeated failures and control measures were not reviewed nor were suggestions implemented across all mines.
6. Officials in Minas Gerais rated the Fundão dam as Class III - its highest level for potential
to cause environmental damage. In addition the independent report produced by Instituto Prístino which also warned of dangers of increasing mine height. However, Samarco provided its own independent report which judged the dam as safe. The officials of the state Secretariat of the Environment visited the dam in October 2014 and considered it to be safe, but they were not engineers.
WHERE DO WE STAND Many of the above mistakes can also occur at mining sites in India. However, we are fortunate to have a robust mining legislative system with active monitoring mechanisms in India. A. The Indian Bureau of Mines published a Manual for Mining Plan that details the steps
needed for proper tailing dam management that includes:
1. Getting complete details regarding physical and chemical characteristics of tailings, their possible reuse, if any along with the design, size and capacity of tailing pond.
2. Furnishing of details of process of water treatment, if any and quality and quantity of final discharge and the place of its disposal (proximity to rivers, public well or any other public utility places) in the Mining Plan
3. Tailings Dam Management: The steps to be taken for protection and stability of tailing dam, stabilization of tailing material and its utilization, periodic de-silting measures to prevent water pollution from tailings etc, arrangement for surplus water overflow along with detail design, structural stability studies, the embankment seepage loss into the receiving environment and ground water contaminant if any, needs to be detailed out and described.
4. Having a detailed Disaster Management Plan and Risk Assessment: detailing action plans for high risk accidents like landslides, subsidence flood, inundation in underground mines, fire, seismic activities, tailing dam failure etc. and emergency plan proposed for quick evacuation, ameliorative measures to be taken etc. The capability of lessee to meet such eventualities and the assistance to be required from the local authority may also be described.
B. Tailing Dam design and its management form an integral part of the EIA report for getting
the Environmental Clearances. Environmental Appraisal Committee while grant of Terms of Reference also prescribes detailed study to be conducted on tailing management from Institute of Repute after due validation. Ministry of Environment & Forests is also in process for formulating specific guideline towards Management of Tailing.
C. Central Pollution Control Board & State Pollution Control Boards stipulates condition in Consent to Operate under Air & Water Act for Tailing Dam Management and ensures compliance by way of regular visits.
Page 7 of 7
WAY FORWARD Also, mining companies in India should adopt pro-active measures that include:
1. Proper design of tailing dam, using geo-technical knowledge and engineering experience
to make safe tailings dams. Dams are designed with a high factor of safety. In many cases, the dam is strengthened with impervious lining.
2. Strong Tailing Dam Monitoring Systems - lack of monitoring and maintenance of tailing dam is the primary cause of tailing dam failures. Proper maintenance and repair of water diversion channels and storm freeboard is essential to prevent such occurrences.
3. Recoding and monitoring movements in the dam wall using Slope Stability Radar and other monitoring systems with provisions for remote alarms.
4. Reducing the need for tailing dams and storage of slimes: Dry Tailing System for Concentrate Tailings and Centrifuge Systems for effluent sludge at the Effluent Treatment Plant for safe disposal without need for tailing dams. Additionally, the ability to recycle the water is a big plus.
5. Hazard Identification and Risk Assessment should be done in detail for the tailing dam construction and management at the conceptual stage itself considering the engineering, geotechnical as well as the process aspects. Mitigation measures should be drawn out and documented in the form of Safe Operating Procedure (SOP) & Work Instructions(WI). Regular Job Cycle Checks, and safety visits should be made; incidents/ observations/ near misses should be recorded and reviewed at highest possible level. Based on the on the review and a “why-why” analysis, the SOP should be reviewed and communicated to all concerned for utmost adherence in the field.
6. Emergency Preparedness & Response Plan need to be meticulously drawn with proper action plans and defined responsibilities. Mock drills need be done at regular intervals to identify the gaps and the SOPs revised. Mitigation plans need to be drawn up accordingly. These plans should be regularly communicated to all concerned in form of periodic trainings and mock drills.
ACKNOWLEDGEMENTS This article uses publicly available images and publically available information sourced from the internet for illustrative purposes only. No copyright infringement is intended and all rights reside with the original copyright holders.