June 1, 2009
By AECOM Canada
Wastewater from the Chisel North Mine near Snow Lake in northern Manitoba had been fed into a former open pit mine at the site for several years. When the owner, HudBay Minerals, asked AECOM Canada to...
Wastewater from the Chisel North Mine near Snow Lake in northern Manitoba had been fed into a former open pit mine at the site for several years. When the owner, HudBay Minerals, asked AECOM Canada to do a study of the mine’s existing wastewater treatment plant, the study showed that the plant was not capable of treating the water fast enough. Within a year untreated water in the pit might have risen to levels where it could breach the south dam and spill into the surrounding environment. The primary element of concern was the presence of zinc, which is at levels exceeding 70 mg/L before treatment.
With some urgency HudBay Minerals asked AECOM to help find a solution. They considered treating the water in-situ, upgrading the existing plant, or discharging the water into another tailings area.
During the course of the study, however, Millennium Mechanical Contracting, a mining contractor, discovered that a decommissioned 2,500-gpm water treatment plant was available at the old Geco Mine site in Manitouwadge, northern Ontario, a mine formerly operated by Falconbridge. The team realized it was possible to re-use the Geco plant and after visiting and doing a cursory inspection, AECOM was invited by HudBay to present a proposal for relocating the plant the 1,700 kilometres to Snow Lake for refurbishment.
The plant had been decommissioned a full 10 years before. Having studied the plant and established that it would fit the needs, AECOM developed a plan to assess the existing equipment, to dismantle its parts and repair any components as necessary. The plant was then transported via several trucks in pieces to the Chisel North Mine for reassembly.
The rehabilitation took 50,000 man hours with no safety incidents. The work mainly included removing scale, refinishing the surface of the clarifier and tanks, and general maintenance of the mechanical equipment. Major pieces of equipment such as the clarifier rake arms and reaction tank mixers did not require significant repairs. Improvements were made such as adding a modern DCS control system.
Even the building to house the plant was re-used: Hud- Bay purchased a salvaged crusher building for the purpose, and it was located on an abandoned section of the mine site, where the old hoist room dry complex was once located.
Since May 2008 the relocated plant has been running effectively, and by this spring had lowered water levels in the Chisel Pit by more than six metres.
Originally it was thought that a new water treatment plant at the Chisel North Mine would cost about $12 million and would take more than two years to complete. The re-used plant was provided for approximately half the price and in less than half the time.
Prime consultant (engineering/contract administration): AECOM Canada, Winnipeg (Barry Williamson, P. Eng., Curtis George, Blair Moore, P. Eng.). Client: HudBay Minerals Contractor: Millennium Mechanical