Enviro Liner - Mining
Location: Yukon, Canada
Timeframe: 1st Phase - Fall 2009 2nd Phase - 2012
Project Owner: Yukon Zinc
Background Information and Challenges
Yukon Zinc's Wolverine Mine is a high-grade zinc-silver-copper-lead-gold underground mine, with on-site milling capabilities of producing 1,700 tonnes per day of zinc, copper, and lead concentrates. The Wolverine Mine is located in southeast Yukon, Canada. Yukon Zinc completed major site construction at Wolverine Mine throughout 2009 and 2010. Mill commissioning commenced in late 2010 and operations started in 2011. In March 2012, commercial production was achieved and in Q1 2013, full design capacity was reached.
The milling process produces tailings, some of which are deposited in the tailings facility. The tailings have high sulphide content and have the potential to become acid generating if allowed to oxidize. Therefore, tailings need to be stored in a saturated containment system.
Layfield was involved during the design process to ensure that the construction of the facility met the stringent design criteria and quality assurance from a geomembrane design perspective. The starter dam and base of the tailings storage facility were lined during the first phase of the project. In the second phase the height of the dam was raised and the upstream face of the ultimate dam was lined to complete the tailings storage facility.
One challenge was to choose the proper material for this application as various lining options were considered, including clay liners. Flexible LLDPE based Enviro Liner 40 mil and 60 mil were chosen to line the tailings impoundment and the upstream dam facing, respectively. A non-woven geotextile was laid over the subgrade to protect the liner from subgrade imperfections.
The project was based on tight deadlines as the mill was to be in operation in 2010.
In the second phase of the project the liner was directly extrusion welded on to the existing liner that was installed in 2009. It was imperative that all dirt and moisture were removed from the existing liner surface to ensure a proper weld could be performed.
The greatest challenge faced during the liner installation was the temperature differential in the month of August 2009. The fluctuation in temperature caused the polyolefin sheet to contract at low ambient temperatures (-30C). Some degree of tenting was observed, and tenting can cause the liner to stretch at the toe of the slope, and in some cases the liner may rip from the anchor trench if enough slack is not incorporated into liner. The client also had concerns regarding the cold temperature performance of the material.
Layfield worked with the Owner’s Engineering firm and provided a geosynthetics option. The geosynthetics option was considered by the Engineering firm as it offered better performance against the tailings and also mitigated the effects of oxidization and leaching caused by sulfide-rich mine tailings on clay lined impoundments. In the first phase the base of the tailings impoundment was lined and the liner was anchor trenched on the 6 mtr wide crest.
The thermal expansion and contraction properties of the geomembrane were carefully considered and enough slack was designed into the liner to prevent tenting. Extensive field experience is required to properly estimate the slack in a liner when dealing with frequent temperature changes. One of Layfield’s experienced field installers was initially confounded with the temperature differential on site but was able to solve the issue in a timely fashion.
The Enviro Liner geomembrane has excellent cold temperature properties and can be installed in -30 degrees Celsius. Please refer to Layfield’s Cold Temperature Handling Guide for more information.
The second phase of the project involved extrusion welding around the perimeter of the existing liner.
This was accomplished by our liner installation crew, and the QA/QC was maintained and provided to the owner.
After phase one installation, Yukon Zinc recognized the contractor and Engineering firm in their monthly newsletter (October 2009). It read: “The tailings dam geomembrane liner installation has been completed ahead of schedule and is a significant step towards completing the tailings facility”. Layfield was also on budget and on time for phase 2 and the tailings storage facility was completed as per the schedule.
Layfield recently followed up with the Environmental Superintendent of the mine regarding performance of the liner. He commented: “The liner seems to be performing fine. No leaks have been detected to date, and the liner looks like it is still in good condition”.