There are three main types of water at Henty
Below are described the potential IMPACTS of the various types of water on the environment, and the ACTIONS that the mine takes to prevent or minimise these impacts.
Stormwater falling on disturbed areas on the mine-site (eg roads, ore stockpiles, etc) picks up clays and dust from the ground. If it falls on areas such as the processing mill, or vehicle workshop areas it could become contaminated with chemicals used in the mill, or oil and diesel or other fuels. If this muddy or contaminated water were allowed to directly enter the local river systems, damage to the rivers' ecosystems could occur.
Mill and workshop areas are all constructed on concrete aprons, with walls or "bunds" around them to contain any spillage.
This fuel storage area is constructed on a bunded concrete apron.
Stormwater draining from these areas, and from gravel roads and other disturbed areas, is drained into special settling ponds where the suspended clays settle out.
Settling ponds
The clear water is then either discharged into an artificial wetland area for further cleaning (see below), or recycled back through the processing plant, or sprayed on roads around the mine when dust control is necessary (see Land).
These pumps can direct water from the settling ponds to other parts of the mine, for example back to the process plant, or for use in dust control when necessary.
Underground water discharged from rocks in the underground workings contains dissolved metals and can be quite acidic. If released directly into the environment, it could cause contamination of local rivers, lakes and ecosystems.
After passing though the settling ponds, this water also flows through the artificial wetland. Contaminants are extracted from the water by the peat lining in the base of the wetland, and by plants growing in the wetland. By the time the water reaches the end of the wetland system, it is very similar in quality to water found in natural Tasmanian wetlands and can be safely discharged into the Henty River. That the wetland is a healthy environment is indicated by the fact that platypus, frogs and other animals, as well as numerous species of native plants live in the wetland.
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The artificial wetlands. |
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The good health of the wetlands is indicated by the presence of an active ecosystem, including platypus
Gold and silver are leached from the ore in the process plant using water containing dissolved cyanide. The left over material is called leach residue and is a muddy slurry of finely ground sulfide minerals and volcanic rock mixed with cyanide-bearing water. If it were released directly to the natural environment it would be highly toxic to animals and plants living in the area.
The leach residue undergoes treatment to remove the cyanide. The treatment involves
The large green tank on the right is a thickening tank used to extract some of the cyanide-bearing liquid from the leach residue. The yellow tanks are used to detoxify (remove residual cyanide) the liquid remaining in the leach residue after thickening.
After thickening and detoxification the amount of cyanide in the leach residue slurry is below environmentally safe levels. The detoxified leach residue passes through plastic pipes to the Leach Residue Pond (see Waste). Here the solid finely ground non-valuable rock material settles out from the liquid. The now clearer liquid is decanted off and pumped into a water pond for further clarification before discharge into the Henty Canal.
