HEAVY metal pollution is still leaking from an old coalmine into a river in the Blue Mountains World Heritage area, a year after government tests showed that it was killing aquatic life.

It will take more than a century for life to return to Dalpura Creek, near the Grose Valley, unless the run-off from the disused Canyon Colliery can be diluted or stopped, according to an independent report commissioned by the NSW Government. Zinc and nickel levels near the mine are 500 times higher than safety guidelines in some cases.

The report confirms earlier findings by a University of Western Sydney researcher, Dr Ian Wright, that discharges from the mine are chronically toxic to the small water creatures which form a basis to the local food chain.

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The State Government said yesterday that heavy metal levels had fallen since the late 1990s but ”would remain significant for some time”, and it was monitoring the situation.

”The … report concluded that the best-ranked option was ‘natural attenuation’ of the heavy metals in the groundwater,” a Department of Environment spokesman said.

”The report also recommends ongoing water quality monitoring and assessment, along with further desktop feasibility of capturing and treating the effluent and meshing the outlet pipe for safety precautions … It is important to note that while elevated zinc levels are a problem for aquatic life, they are not a health concern for people.”

But the report says that while ”natural attenuation”, or allowing the pollution to decrease by natural processes over time, was the easiest way of addressing the problem, ”this option cannot be justified on the basis of the current data”.

It said a proper clean-up could be expensive and tricky in the river gorge, which is only accessible on foot. The possibility of using explosives to collapse the sandstone cliff and bury the mine’s water sluices was examined. But it concluded that, given the river is ”located in a World Heritage area, it is highly unlikely that the [National Parks and Wildlife Service], let alone [the Department of Environment] or the greater public would support such drastic action”.

The mine’s former operator, Coalpac, undertook an assessment of the polluted sluice in 2001 and decided on a ”do nothing” option, because it would be costly and the results would be uncertain. It argued that because the mining lease had expired, the pollution was no longer its problem. The mine was closed in 1997, but the sluices were never sealed because the company believed the problem would vanish over time.

The Opposition spokesman for the Blue Mountains, Michael Richardson, said the Government had been sitting on its own findings for a year without taking action to reduce the pollution.

”Nothing has happened since,” Mr Richardson claimed. ”Heavy metals continue to impact on the World Heritage Area while decisions are delayed. More metals will accumulate if the Government decides to monitor rather than fix the problem.”

The report, produced by consultants from the Snowy Mountains Engineering Corporation, also confirmed earlier suggestions that the closure of a sewage treatment plant upstream in Blackheath last year had accentuated the river pollution. The reduced flow meant that the heavy metals from the mine were more concentrated.