Summary: Surface Water
Dr Ian Cordery, Associate Professor, School of Civil and Environmental Engineering, UNSW
A significant issue of concern is that free erosion of many millions of tonnes of waste and surface wash off material will enter the Frieda River in the early construction phase of the mine, prior to completion of the Integrated Storage Facility (ISF).
– During construction of the ISF (years -5 to -1), the waste heap will be allowed to erode into OK Binnai and Ubai Creeks, which will then pass unrestrained into the Frieda and Sepik Rivers.
– Flow velocities over the Frieda River floodplain are likely to be small which will deposit fine sediment onto the floodplain. This will render the floodplain unproductive for a number of years and villagers reliant on this to subsist will not have access to it for considerable time.
– In a region where the annual rainfall is very high, this lack of restraint on movement of sediment from the waste dump is unacceptable. Minor sedimentation ponds at the toe of spoil piles will not be adequate to contain the sediment.
– The EIS states that up to 4 million tonnes of sediment will be deposited in the Frieda River, which is likely to be a gross underestimate. The amount of sediment could be double this figure.
– The escape of these sediment loads during the first 3 or 4 years of construction is not acceptable. The construction plan should be revised to avoid this.
– The uncontrolled erosion of the copper and aluminium rich spoil dump adjacent to the limestone quarry should not be permitted. Measures should be put in place prior to development of the spoil dump to prevent this, such as a large sediment trap downslope of the dump.
How the potential for dam break will be managed post closure, including who is responsible for funding and carrying out activities, as well as emergency response, are not detailed. It would be appropriate to obtain the expected costs of these activities from the proponent prior to mine closure.
During mining operations, concentrations of toxic dissolved metals (copper and aluminium) in the Frieda River are expected to be very much in excess of those considered acceptable for drinking water.
The levels considered in the EIS to be acceptable for discharge for copper and aluminium are much higher than those recommended in Australia and New Zealand (6 times higher for aluminium and 20 times higher for copper). They appear to be chosen for financial convenience rather than protection of people.
Water treatment is stated to be needed after mine closure for up to 50 years, however there is no detail of how this will be managed post closure, or who is responsible for the costs involved. Provision of funding and managing of these operations to be put into the Conditions of Approval for the mining activity.
Oversight of a number of post mine closure activities are not detailed in the EIS, and will require significant resources to carry out. Who is responsible for these activities is also not clearly articulated in this report.