Contact Energy Limited has been convicted and fined $162,500 over a major incident at its Wairakei geothermal field, impacting on the Huka Falls and Waikato River in February 2019.
Judge David Kirkpatrick released his sentence for the company's unlawful discharge of geothermal fluid and sediment in the environment yesterday from the Taupō District Court, arising from an investigation by Waikato Regional Council.
The investigation focused on the Contact Energy's large geothermal power plant at Wairakei, north of Taupō.
At the plant, the company's process was to transfer used geothermal fluid through long sections of steel pipe back into the earth. On occasion, the pressure built up requires release from the pipe system, with alarms activating at Contact's control room to ensure this is safely managed.
However, when the alarm was triggered in February 2019, after excess pressure was automatically released, it was not responded to for six days.
This resulted in approximately 44,000 tonnes of geothermal fluid being released into a soakage pond over that six-day period.
As the pond was only designed to receive relatively small volumes of fluid, it built up to the point that the pond collapsed.
An estimated volume of 15,000 cubic metres of soil laden with geothermal fluid discharged across the adjacent farmland for approximately 60 metres, before flowing into the Waipouwerawera Stream.
The discharge caused significant damage to the stream as it travelled 930 metres before flowing into the Waikato River, at a point 1.2 kilometres upstream of the Huka Falls.
As a result, the large amount of soil turned the river a dark muddy brown, which continued over Huka Falls and downstream for 6.5km to the Aratiatia Dam, and then a further 7km until it began to clear.
Council regional compliance manager Patrick Lynch said this had been a particularly significant environmental incident.
"Contact is a highly compliant company with very high standards. However, this incident reflects that an enterprise of this scale, operating in such a sensitive and valued environment, has to have absolutely foolproof systems that are checked and re-checked regularly," he said
"This incident shows that when things go wrong in an operation of this size they go spectacularly wrong.
"I know this incident and the subsequent prosecution has had a significant impact on Contact and they have carefully analysed and addressed their faults."
Lynch said the council wanted to acknowledge the significant role the Tūwharetoa Māori Trust Board played immediately following this incident and during the subsequent court case.
"Their knowledge and input assisted greatly in identifying the widespread impacts of this incident and how they can be addressed," he said.