Ok Tedi Mining

Mining at Ok Tedi has caused environmental impacts that are significantly greater than were projected at the time of mine planning and commissioning in the 1970s and 1980s.

Each year, the Ok Tedi mine discharges about 90 million tonnes of waste rock and tailings (mined and crushed rock after approximately 85 per cent of the copper has been removed) into the Ok Tedi ('Ok' means 'river' in the local language). This discharge is carried out with PNG Government approval.

Over its first 20 years, the mine had the greatest impact on the Ok Tedi. The river bed has been raised in the upper Ok Tedi by several metres due to the rock and sand released into the stream from waste rock and tailings. In the lower Ok Tedi, where the river leaves the foothills of the Star Mountains, over-bank flooding is common because of higher river bed levels and this impact is now extending well into the middle reaches of the Fly River.

Sedimentation and vegetation dieback

The build-up of mine-derived sediment in the lower Ok Tedi and Fly River has caused a rise in the river bed, resulting in over-bank flooding and sediment deposition on the flood plain. The increased inundation stresses and, if prolonged, kills flood-sensitive vegetation along the riverbanks and on the floodplain. This phenomenon is known as "dieback".

OTML monitors the amount and distribution of dieback through satellite images together with ground truthing surveys. Dieback is progressively increasing as the amount of sediment in the rivers increases and moves downstream. Based on the observed dieback over the past 12 years, and extensive modelling undertaken for the Mine Waste Management Project, the maximum amount of forest affected by dieback may eventually reach about 3,000 square kilometres. At 30 June 2005, the total area of forest affected by dieback was 1,588 square kilometres.

The forest affected by dieback is predicted to slowly recover by natural processes once the mine closes and release of sediment stops. In the middle reaches of the Fly River, it may take 200 years or more for much of the sediment to pass through and the river return to something like a pre-mine condition.

Regeneration of areas affected by dieback has been recorded in the lower Ok Tedi over about 150 square kilometres, with most of this associated with reduced flooding due to removal of sediment by dredging at Bige. An additional 380 square kilometres of dieback affected areas in the Middle Fly is also undergoing recovery.

The flooding, causing dieback and other changes in vegetation, has affected people living in villages along and in the vicinity of the rivers. The major impacts include loss of gardens, reduced supplies of sago palm (a staple food source), increased effort for food gathering and more difficult travel across the flood plain. These people are compensated under a number of compensation arrangements.

Other impacts

Copper levels in the river system are elevated and are increasing due to copper in mine waste. As the levels are still well within Australian, PNG and World Health Organisation drinking water standards, there is no indication of a risk to human health. However, the current levels of bio-available copper are sufficient to adversely impact the river ecology and may impact on the number of fish in the middle Fly River.

Sulphide minerals deposited in mine waste sediments have the potential to generate acid when exposed to the air; a process known as acid rock drainage (ARD). This reduces water pH and mobilises metals. Small areas of ARD have been known for some years along the upper Ok Tedi.

In early 2005, areas of acid rock drainage, appearing as dead grass and bare soil, were found along the levee banks in the lower middle Fly between Manda and Everill Junction and at some places in the upper Middle Fly. These appear to have been caused by sulphide-rich mine sediments deposited over an extended period of flooding during 2003-4, which then oxidised when the floodwaters receded.

Sulphide levels are also increasing in the Bige dredge stockpiles, and modelling of future levels indicates that the stockpile sediments are potentially acid forming and likely to generate acid without mitigation.

Feasibility studies are currently underway for mitigation options to tackle the ARD and copper impacts discussed above. These are outlined in the managing mine waste section of the website.

Compared to pre-mine levels, fish numbers have dropped significantly in the Ok Tedi and the Fly River below the Ok Tedi junction and down to the Strickland River junction. This is thought to be due to sediment smothering fish habitat in the main river channels and more recently it appears possible that water chemistry is having an impact. Fish biomass is monitored under the company's environmental regime and sampling in 2005 shows there is sufficient aquatic food resources to meet normal community demands.

Detailed information on the numerous environmental, health and engineering studies undertaken to investigate the impacts of mining can be found in the Reports section of this website.