ISLAND COPPER - Aquatic Areas
The Pit Lake
In 1996, the open pit was flooded with water from Rupert Inlet, temporarily creating the world’s largest marine waterfall. This flooding created a meromictic lake (which remains stratified and does not circulate) with brackish water stratified over salt water. The lake is approximately 365 m in depth. The pit lake is currently used as a passive in-situ ARD water treatment system for mine water. As the ARD water is injected at depth into the pit lake (below thermo and chemoclines), it mixes and reacts with the salt water to form a stable metal sulfide precipitate, which settles at the bottom of the pit lake. Water discharged into Rupert Inlet is from the top layer of the pit lake, which has reduced metal concentrations.
Anoxic conditions must be maintained in the lake bottom to promote the activity and population growth of sulfate reducing bacteria; thus, the stratification of the lake must be maintained and mixing must be prevented. Specifically, dissolved oxygen must be below approximately 1 mg/L in the intermediate and lower layers of the pit water. The lake’s stratified condition can be maintained with management for over 1000 years, while the ARD potential of the mine is less than 1000 years.
The Beach & Foreshore Area
The majority of the tailings were placed on the foreshore area creating a 262 ha 'beach'. Almost 95% of the beach dump volume is below sea level in Rupert Inlet. The beach dump was contoured into six bays and was graded to the low tide mark to promote aquatic habitat. Intertidal and subtidal areas were colonized quickly by marine organisms from Rupert Inlet. As part of the consideration of recreational opportunities the beach was not only contoured with aquatic habitat in mind, but also to visually appeal to recreational users in the area. As of 2000, this engineered environment was indistinguishable from the reference station. Organism colonization of the beach dump at the bottom of Rupert Inlet is at pre-mining levels; this includes colonization by benthics, juvenile salmon, dogfish shark, rock cod, and Dungeness crab. In 2010 it was reported that the angular rocks used to create the beach were becoming rounded from the wave action in Rupert Inlet.
Wetlands occur on the beach dump in areas where the soil was compressed by vehicle traffic. The wetlands are connected by channels where tire ruts were present during operations. Wetlands were constructed and planted with wetland species in order to trap sediment and treat runoff from the site. Biodiversity on the mine site has increased with the addition of these wetlands.
Water from the pit lake, IC's passive water treatment facility, is discharged into Rupert Inlet
Rupert Inlet is approximately 10 km long and 1.5 km wide. The main freshwater input into the inlet is from the Marble River, with water from IC contributing a much smaller input. Currently, there is a salt water lagoon located in the old flood channel connecting the Pit Lake to Rupert Inlet. It had been intended to keep the flood channel between the pit lake and Rupert Inlet open; however, due to water quality concerns the pit lake was sealed off, resulting in the creation of the lagoon.
Stephens Creek Watershed
Twin Lakes are two freshwater lakes located on the north side (inland side) of the pit lake. The lakes are fish bearing and drain into Francis Lake, which eventually drains into Stephens Creek and Holberg Inlet. Species that reside in the Twin Lakes system include coho salmon, cutthroat trout and Dolly Varden char. Seepage from the north waste rock dumps was found to be impacting water quality in Twin Lakes. During operations Francis Lake was used as a source of freshwater. Species of fish that inhabit Francis Lake include: cutthroat trout, coho salmon, Dolly Varden char, and threespine stickleback. Each year the Stephens Creek watershed is stocked with coho salmon.
Although diversion systems were constructed to prevent mine seepage from impacting Francis Lake, elevated zinc still became an issue. As part of the risk reduction for the Twin Lakes area, a diversion project with habitat compensation was undertaken. Seepage is diverted into the Pit Lake for treatment before being discharged into Rupert Inlet. Performance monitoring of this project will be ongoing to ensure that the Stephens watershed remains unaffected as mine chemistry conditions change over time.