Yes, and there are many good examples such as Mt Morgan gold mine and acid mine leachate (drainage) from tailings entering the Dee River.
Yes, runoff or subsurface water movements from a mine within the catchment of the Sydney dam could contribute to the water quality in the dam, but to say that the black sludge at the bottom of the dam are ‘are a by-product of coal-mining activity’ is a little hard to believe.
If the black sludge was from a mine, this would assume that there would be little influence of other land uses on the sedimentation of the dam. There is overwhelming evidence that any disturbed land uses, including agriculture, forestry, roads etc contribute to downstream sedimentation. Even undisturbed natural areas contribute to downstream sedimentation through natural weather and erosion processes.
As the dam catchment contains both disturbed and undisturbed landscapes, all these would contribute to sediment collecting in the base of the dam.
It is also worth noting, possibly for ‘balance’ that the ABC article indicates that further research is needed into why metal concentration are elevated.
The impact of mining in water catchments was last year probed by an independent expert panel appointed by the office of the NSW chief scientist.
The WaterNSW spokesperson said that study “did raise concerns about the potential for metals to enter dams in the long term” but that more research was needed
Looking into the area a little deeper, only one mine appears to be within the catchment of Cordeaux Dam, that being Cordeaux Mine. This mine has been closed for close to 20 years and has limited surface disturbance (there is no evidence of tailings from coal washing or from other activities).
It is also worth noting from aerial photographs there are two active mines to the east of the dams, which are underground operations. The surface work and stockpile areas for the mines are within catchments which flow to the east and are not within to the west to the two dams in question.
This would indicate that if there was a potential impact of mining activities on dam water quality, it would be a result of the underground workings and seepage from these workings to the surface water catchment of the dam and not from sediment from surface mining activities.
As the area has high relief, the soils on upper levels will be highly oxidised and contain high concentrations of sesquioxides, like other Australian soils in similar locations. These sesquioxides will principally be of iron and aluminium forms and their presence can be readily observed through the ‘rusty’ orange to red colours of the soil.
It is also worth noting that the article may be the result of the environmental group Protect Our Water Alliance, which has been demanding from the government the cessation of coal mining beneath the Sydney dam water catchments. The Alliance also has stated that Peabody’s Metropolitan mine
has submitted plans seeking permission to begin mining the next longwalls, it is likely these plans are for LW305, 306, and 307, which will run directly under the dam itself. We have been advised the Planning Minister Rob Stokes will make a decision about whether to proceed with these sometime over the next couple of months."
This may go to the heart of the ABC article.