Project Description

The Tundra Mine site is located approximately 200 km NE of Yellowknife. Delta Nahanni Joint Venture (DNV) was awarded a one-year contract to perform the remainder of reclamation activities, which included: contaminated water treatment/water management; relocation and consolidation of tailing deposits; installation of geomembrane and geotextile within the tailings containment area (TCA) and aggregate material production and placement; PHC soil excavation and treatment/disposal; instrumentation; and demobilization and restoration activities, including demobilization of crown materials once the job was completed

Water that was contaminated with heavy metals and other contaminants in concentrations above permitted discharge criteria was treated using the iron c0-precipitation treatment method in a water treatment plant DNV constructed on-site. Water treatment was completed before the consolidation and capping of tailings. Once treatment of water was complete, the water treatment plant was deconstructed.

DNV was responsible for monitoring and implementing the 2017 Freshet Monitoring & Response Program. The program required site presence to ensure no discharge of silt laden water to surrounding bodies of water and to administer necessary pumping measures when needed. Pumps and discharge lines were positioned in appropriate areas determined by geographic mapping and monitored 24 hrs/day during freshet. Silt curtains and erosion protection measures were installedtwhere necessary.

Significant water management and water pumping infrastructure was required to accomplish tailings consolidation. In one case a cumulative discharge rate of 275 m3/hr had to occur from one of the onsite pond storages to allow for appropriate treatment and consolidation.

Geotextile and bituminous geomembrane were installed over the relocated tailings. Landform cover was designed to shed water into the DNV constructed diversion ditch and installed after bituminous liner and cover material was in place.

PHC soils identified at the site were excavated and either treated on site or containerized for off-site disposal. A Water Board approved treatment plan identified landfarming as the approved process.

DNV was responsible for instrumentation of groundwater monitoring wells, vibrating Wire Piezometers, thermistors, and Survey Control Monuments.

Demolition and restoration activities included: removal and disposal of HDPE piping and of HDPE geomembrane liner; levelling and reshaping tank farm and hazmat area berms; decommissioning of sewage lagoon and sewage system; removal and disposal of silt fencing/silt curtain, installation of bituminous geomembrane, and of culverts; and scarification of roads.

While on site, DNV was also responsible for organizing all on-site support services. These responsibilities included organizing logistics, maintaining camp facilities, shipping and handling of freight and organizing air charters for transportation of employees and supplies.

CHALLENGES

  • Site was only accessible by road on a 35 km DNV constructed winter spur road at KM-266 off of the Tibbitt-Contwoyto Winter Road for a short period of time, making logistics planning for mobilization and demobilization a key factor in successful completion. Winter road capacity had to be calculated by a certified engineer and approved by WSCC prior to use.
  • All other transportation needs had to be coordinated by air with an operational gravel airstrip 1.5 km N of the site
  • Extreme weather temperatures that included +30 to -50 celcius swings from summer to winter operations.
  • Health & Safety – hydrocarbon contaminated soil and waste rock and mine tailings with high concentrations of arsenic and other metal contaminants required a well-coordinated safety program.
  • Wildlife protection – DNV had a wildlife monitor on site 24hrs/day
  • Tailings consolidation could not be completed until tailings water has been treated and discharged
  • Aggressive schedule required us to have a 24 hours operational camp (night and day shifts), a suitable equipment fleet and a strong maintenance program
  • Being an isolated camp we had to develop a suitable waste management program