Samarco maintained, until November 5, 2015, two dams for the storage of tailings resulting from the extraction and processing of iron ore at its Germano (MG) plant. The newest one was Fundão, inaugurated in 2008, with storage of 55 million cubic meters.
The dams were built in line with the National Dams Security Policy (Law 12.334 / 2010), with its own safety inspections and 24-hour shift teams for maintenance and monitoring. Operating licenses were regularly granted by the Regional Superintendence of Environmental Regulation (SUPRAM) – the last inspection before the disruption was carried out in July 2015. In September of that year, reports were delivered to the competent authorities, indicating a safe operational condition for the dams. Regrettably, even with the risk management procedures associated with dams, these measures were not able to anticipate the disruption.
Through the rupture of the dam, Samarco executed its Samarco Mining Dams Emergency Action Plan, presented to the National Department of Mineral Production (DNPM), and Germano’s production process was immediately interrupted.
There were two embargoes on Germano: one from the DNPM, on the operations of the dams and UTM treatment units, and another from the State Foundation for the Environment (Feam) together with the Secretary of Environment and Sustainable Development (SEMAD) , On operations as a whole, except for activities considered emergency (such as structural reinforcement works). In the unit of Ubu, in Anchieta (ES), there was no embargo due to the rupture.
Understand what are and how the structures of a dam work:
- Main dike or dam: a structure made with embankments to contain the tailings.
- Crest: the highest point of the dam, where the deposition of sandy tailings starts.
- Sandy tailings reservoir: place where the sandy waste from the beneficiation process is disposed of.
- Reservoir of fine tailings/slimes: place where the muddy waste from the beneficiation process is disposed of.
- Auxiliary dikes: structures which serve to delimit the areas for tailings impoundment and allow proper handling.
- Abutment: natural terrain at the extremities of the dam into which the dam is embedded.
- Spillway: structure which allows the excess water to flow out of the dam.*
- Internal drainage: structure which allows the water to be collected by the system of internal drains.*
*The water that leaves the internal drainage system and the water that flows over the spillway are directed to the natural course of the stream, at the bottom of the valleys, where they may or may not be abstracted and reused in the iron ore beneficiation process. In Samarco’s case, this water is treated, with a part being recycled in the production process and the rest released into the environment.
In the process of iron ore beneficiation, the material extracted during mining is separated – the ore is directed to the production of pellets, while the mixture of water, together with particles of iron oxide and silica or quartz (the tailings), is disposed of.
As the tailings are deposited in the dam, the solids settle to the bottom and the water comes to the surface. The water is then drained or skimmed off and treated, with part of it being reused in the beneficiation process and the rest returned to the environment.
The tailings mixture does not contaminate the water nor does it represent a hazard to human health. Learn more about the composition of the tailings in this video:
The sediment retention system and the safety of remaining structures
In order to comply with the guidelines of the Civil Defense and the Fire Department and with a view to reducing risks, the Company adopted additional measures and started construction on the dams to ensure the safety of the remaining structures and contain the tailings flow. Check the stage of the initiatives in each structure:
Selinha dike: Structural reinforcement works were completed in December 2015. At present, surface drainage works are carried out to avoid erosion. Completion is scheduled for April 2017.
Sela and Tulipa: works divided into three phases; The structural reinforcement phases 1 and 2 were completed in September and November 2016 and the sandy and tailing phase 3 filling and leveling of the area near these dykes was completed in February 2017.
Germano Dam: Reinforcement of the foot of Germano was completed in June 2016. In December of the same year, improvements were completed in the drainage of the structure.
Remaining waste retention barriers (sections 1, 2 and 3) were completed in 2016. Section 4 was completed in early 2017.
S1 and S2 dikes: the barriers are just below the Santarém dam and were completed and silted. The structures are responsible for the containment of existing sediments in the area of Fundão and Santarém.
S3 and S4 dikes: S3 and S4 dikes, with the new Santarém dam and S1 and S2 dikes, make up the remnant waste retention system of the Fundão Valley and improve the water quality of the Santarém stream.
Nova Santarém: the first interventions on the site, completed in February 2016, were works to reinforce the old dam. The adjustments ensured a higher safety factor of the structure. Following this, the first phase of construction of the new Santarém Dam, completed in December 2016, was initiated. This is one of the most important milestones in Samarco’s goal of containing the remaining tailings of Vale do Fundão. At this stage, the reservoir has a holding capacity of more than 5 million m3. In the second and last stage, carried out between March and June 2017, the capacity of the reservoir was raised to 7 million m3.
The sediment containment system implemented by Samarco in Mariana (MG) brought positive results. As early as 2017, monitoring of water in the area indicates a significant reduction in turbidity levels. Since mid-January, water turbidity rates just below S4 dam are below the limit of 100 NTUs (UNEP) established by Resolution 357 of the National Environment Council (Conama). In the case of dam S4, for example, the average turbidity of the water fell to 25.7 NTUs on the last day of February 15. The dike S4 has the objective of avoiding, as far as possible, the transport of solids from the Bento Rodrigues area to the Rio Gualaxo.
Understand the structures in the video below:
Monitoring and safety
To make sure that the dam structures remain stable, Samarco has deployed many different forms of monitoring, such as the use of equipment to measure the pressure and level of the water, the use of special radars, on-site and remote inspections (from the monitoring room) and the execution of reinforcement work and small emergency interventions in the structures.
Since the failure of the Fundão dam, the monitoring, safety and environmental processes have been reinforced, counting with actions such as:
– 24/7 monitoring – drones, field inspections, water level and pressure indicators help the team which is specialized in the monitoring of the structures.
– Reinforcement work – construction of dikes and small containment barriers. Structures are being build in Samarco’s area to prevent the tailings from being carried away by rains into the rivers. The construction of Dike S3 was concluded on 21 February and was raised, increasing its containment capacity to 800 thousand cubic meters. With Dike S4 finished, the emergency system for sediment containment is complete, also including Dikes S1, S2 and S3 and the new Santarém dam, as well as the Fundão structures of Axis 1 and the four internal barriers.
– Pumps for removal of water – five pumps installed to direct rainwaters for treatment at the Germano plant
– Water treatment – the water from the Santarém dam is being treated so that the sediments stay at the bottom and do not follow the water way.
After the rupture of the Fundão dam, Samarco began to elaborate and support specific actions of training and community empowerment regarding emergency situations. In addition, it has made improvements in the communication systems of these situations and in the monitoring of the structures. Throughout 2016 and 2017, actions were performed that represent important learning for the Company.
With regard to communication and mobilization for situations of abnormality, Samarco teams assisted Civil Defense in providing information on the risk scenarios, the flood map and the emergency procedure, which includes the location of the fixed sirens and The location of the meeting points.
Sirens, mobile and fixed, were installed in the dams of Germano and Santarém and in the communities of Bento Rodrigues, Ponte do Gama, Camargos, Paracatu de Baixo, Paracatu de Cima, Pedras, Campinas, Gesteira and Barra Longa. 24-hour online monitoring of cameras, screens, drones and radars, dam instrumentation, field inspections and visual monitoring of remaining structures was also strengthened.
Another motive was the performance of simulation – an opportunity to prepare communities, competent bodies and Samarco itself to deal with hypothetical situations of dam rupture. There were two events in 2016, one in March and another in November, in which the Civil Defense of the municipalities of Mariana and Barra Longa, together with the Civil Defense of Minas Gerais, carried out emergency simulation exercises in the 10 affected communities in Mariana and Barra Longa, A joint effort with Samarco, the Military Police, the Fire Department and the Secretaries of Health, Education and Environment.
In November 2017 a new drill was carried out by coordinators of Mariana and Barra Longa’s civil and state defenses (Cedec) in 10 communities. As in other instances, the objective was to train inhabitants and municipal agentes on how to react in the event of an emergency situation. The army had the participation of approximately 350 people from the communities of Camargos, Ponte do Gama, Paracatu de Cima, Paracatu de Baixo, Borba, Pedras, Campinas, Barreto, Gesteira and Barra Longa (headquarters).
The company, jointly with Mariana and Barra Longa’s civil defenses, held meetings beforehand with residents of the community to explain how the drills would be carried out. The drills integrate an Emergency System guided by the norms and procedures that comprise Samarco’s Mining Dam Emergency Action Plans (PAEMB).
The main purpose of simulated exercises is to encourage community engagement to promote a more peaceful environment, enhancing society’s ability to react to adverse events such as a dam rupture, flood or flood.
This is an important initiative to bring to public knowledge, with transparency and practicality, the improved emergency procedures for affected areas in case of hypothetical dam rupture. The actions also represented a tremendous learning for the Company – and can serve to stimulate safer models of operation for the mineral sector, including with regard to the regulatory framework for communicating and managing emergency situations.