Driving past Vale’s Smelter on Regional Road 55, towards Lively, ON, you see a ribbon of small hills dotted with trees and as the undulating landscape streaks by, the odd body of water.
These are our company’s tailings dams. Tailings are the byproduct of our milling process, a mixture of fine mineral particles and water that are kept securely in ponds by dams, and closely monitored.
According to Sudbury-based Trevor Moxam, lead, Project and Shutdown Management, who has worked at our company in tailings management since 2014, there are three main risks associated with tailings dams: 1) seismic (earthquakes and other vibrations) 2) piping failure (when the dam erodes on the inside) and 3) liquefaction (when the soil that the dam is made of instantly liquifies).
“Risk reduction is a top priority,” Trevor said. “A company-wide risk reduction assessment of all tailings areas has been going on for close to 15 years.” From that assessment, a 10-year plan was established that will see all of our older dams updated with more technologically advanced construction materials and monitoring methods.
“Engineering standards in Canada have improved over the years so as part of that continual improvement, we are working towards reducing risks at all of our dams,” explained geotechnical engineer Meagan Shkwarek, who has been working at Vale since May 2021, and is the lead project engineer in Tailings Execution.
‘It looks like a whale’s backbone’
M Dam North was tapped as one of those dams in 2018. The design to reduce risk on M Dam North includes a dam buttress, and foundation improvements along the dam toe. A buttress is a compacted earth-fill structure used for lateral support. As part of these efforts, work began on building a sheet pile wall (projecting supports that create a wall) out of 2,400 square metres of metal sheet pile. Sheet pile is an engineered system, used in a variety of construction projects, retains water and/or soil, and are long structural sections that are driven into the ground and interlocked to create a continuous wall. Due to the uneven bedrock of the Sudbury Basin, the sheet pile wall at M Dam protrudes from the ground at different heights until cut to design elevation. “It looks like a whale’s backbone,” noted Trevor.
Meagan said a project of this size and scale requires an incredible number of materials, equipment and skilled workers. “We used 3,150 tonnes of cement for jet grouting the sheet pile,” she said as one example. “Onsite, we had drillers, excavators, forklift drivers, site supervisors, a professional engineer – around 25 people daily.”
Z’gamok Construction – on the job, ahead of schedule
The risk reduction projects in the tailings area included contractor Z’gamok Construction LP, which is owned by Sagamok Anishnawbek First Nation. The project is located in Sagamok Anishnawbek First Nation’s traditional territory. In consideration of this, the quality of work from other projects and their knowledge of our business, Z’gamok was awarded the first phase of the project. This involved hauling 500,000 sq. ft. of material, re-grading 540,000 sq. ft. of dam slopes within the active tailings area, and the placement of slag aggregate cover to fortify against erosion.
Z’gamok completed the work in just one month, ahead of schedule. Will Sayers, CEO, Z’gamok Enterprises Inc., explained: “With winter approaching, we ramped up production by increasing personnel to mitigate potential weather delays, and this is how we were able to complete Phase II of the project well ahead of schedule.”
Meagan added, “They also worked safety, mobilized quickly to get the necessary equipment and operators, there were no delays, and the results were what we wanted. Because of all of this, we awarded more haulage work to them.”
In keeping with Vale’s obsession for safety, every step of the way, throughout the three-year project, Meagan, Trevor and other team members were monitoring potential safety risks. A team of professional engineers have been onsite throughout construction looking for abnormalities, and ensuring contractors are working to code. “We are constantly considering worst-case scenarios and we manage the potential risks by designing for them,” Meagan said, adding, “Safety is paramount in everything we do.”
Trevor added, “Our continued obsession creates the legacy we will leave behind.”5