Leaking dam safe says Solid Energy

Solid Energy is assuring people at Granity, 32km northeast of Westport, that a dam on the hill behind them poses no threat.

Conservationists had warned that the Stockton mine sediment dam could collapse in an earthquake. It has been leaking at the rate of at least 55 litres a second.

But an engineering report to Solid Energy five years ago said the dam did not need to be built to withstand a strong earthquake because a collapse was unlikely to be life-threatening.

"There is only a very low likelihood that a sudden dam failure would pose a direct threat to life," said engineering and environmental consultants Woodward-Clyde New Zealand (now URS New Zealand). Minimal downstream damage would be expected.

Buller Conservation Group spokesman Pete Lusk said water flowing through the dam was highly acidic.

Solid Energy spokeswoman Vicki Blyth said the company regularly surveyed the dam for any movement. It had recently commissioned consultants to carry out a hazard assessment and a safety review to gauge the possible impact of an earthquake, "though we still believe there is very low risk of failure".

The dam was at present being drained to repair its lining, she said. The 15m-high dam had been drained to 1m and stormwater diverted. Next week Solid Energy would remove the silt at the bottom.

It would then install a 3m-thick, low-permeability clay fill on the inner slope of the dam wall to minimise leaks, Ms Blyth said. The clay fill would also improve the quality of water downstream.

- NZPA