HIGHLAND VALLEY COPPER - Aquatic Areas
Wetland systems have been installed as a potential passive treatment system for metal removal from wastewater and seepage. Bioaccumulation of molybdenum in plant tissues has been observed. Trials from a 1995 closed system were very positive and it is likely that this system will be used to treat mine water in the future.
Pit Lake and Tailings Pond Bioreactors
The conversion of pit lakes and tailings ponds to aquatic habitat and bioreactors began in 1995. Success was considered to be “the development of sustainable, ecologically valuable aquatic resources without large capital investments or maintenance costs”. The reclaimed ponds at HVC are highly used by wildlife, as water bodies in the HVC area are limited.
The reclaimed tailings ponds at HVC mainly provide wildlife habitat, but also provide some removal of aqueous metals through the life processes of aquatic plants and plankton. As those organisms die and sink, they accumulate in the pond sediment. It has been found that summer algal blooms have removed as much as 10% of dissolved molybdenum and 4% dissolved copper in one season from the pit surface layer. The pit lakes at HVC deeper than 50 m have a bottom layer that does not mix. In contrast the pit lakes that are shallower than 30 m completely mix (turn over) in the spring and the fall. To maintain productivity in the deeper pit lakes, they must be fertilized annually with nitrogen (liquid urea or ammonium nitrate).
Fish in Trojan Pond
The first fish (rainbow trout) were introduced to Trojan Pond in 1991 from the Loon Lake hatchery. The stocking rates of rainbow trout and years are as follows:
Weight and length are monitored to determine success and the steady increase in weight and size of the fish indicate a productive rainbow trout population. Bald eagles and other large birds now feed on the trout as they are making use of the constructed spawning channel. Other mammals and ungulates including black bear, moose, deer, and coyotes are using the shoreline of the pond.
Molybdenum management in the tailings ponds will be a long-term issue
On average, Trojan Pond is 4 m deep with a maximum depth of 8 m. The surface area of the pond is 26 ha. Inflow sources include surface water runoff and from surge flow in Trojan Creek. Trojan Creek was constructed to contribute continual flow to a spawning channel.
The surface of Trojan dam was reclaimed by seeding with agronomic grass species and planting native shrubs. Although shrub transplanting was largely successful, there were some losses due to drought stress, tailings salinity, browse by deer, competition from grass species, girdling by rodents, oscillating water levels, and wind erosion.
Aquatic plants were introduced into Trojan Pond through seeding and transplants. Transplants were done successfully in early spring or mid-fall to avoid the frost period and take advantage of increased precipitation. To increase success, transplants had fertilizer pellets applied near their roots and a small rain depression to collect surface water.
Fertilization is required at Trojan Pond to maintain the primary productivity of the 20-25 species of algae present, the base of the food chain in the pond. The microbial activity in the pond acts to remove dissolved metals from the water column. HVC does not attempt to manage for certain species of bacteria, but does aim to have a diversity of species to encourage this biological metal removal.
Trojan Pond may have been able to establish an aquatic ecosystem without management interventions; however, it would have taken a much longer time.