Downside to geothermal energy in Taupo

By JO-MARIE BROWN and NZPA

The extraction of geothermal energy for electricity is being blamed for subsidence likely to damage more than 150 buildings in Taupo within the next 50 years.

Contact Energy draws heat from the Wairakei-Tauhara geothermal field but will now face growing opposition to its plans to extend operations.

A report prepared for the Taupo District Council said at least 126 buildings and 24 homes would suffer minor damage in future because the soil was losing its strength as water and heat was removed from the ground.

Doors and windows are expected to stick and cracks in exterior cladding are likely to appear due to the subsidence, residents have been told.

The situation is not as severe as subsidence in Waihi where hundreds of homes remain at risk of collapsing due to former mines in the area.

But Contact Energy wants to increase its level of extraction from the Wairakei field by 82 per cent over the next 11 years, while another firm, Geotherm Group, wants permission to build a new power station there.

Both are seeking resource consent from Environment Waikato and will now face stiff opposition from the Taupo District Council and residents.

"Council will also be asking that Contact Energy reduce its present take from the field until it can show that any draw-off will not cause further damage," Taupo mayor Clayton Stent said.

Contact's Wairakei power plant re-injects 40-50 per cent of the water it draws up back into the ground at present. The report says subsidence can be minimised if more fluid is re-injected.

Contact's Wairakei generation manager, Murray Stanley, said the company did not plan to change anything in the short term and would push ahead with its resource consent applications. He said it was a fact subsidence occurred when energy was extracted from geothermal fields. The report was based on assumptions about underground pressure trends and the geotechnical properties of the area and until those assumptions were proven, it would be unwise to regard the findings as conclusive. Energy Minister Pete Hodgson also said greater certainty was needed as to what was causing the subsidence before action could be taken.

Mr Stent said the council was seeking a legal opinion on the issue of compensation. "It's not of our making and it's not fair to expect Taupo people to carry the can."

It was thought repairs could cost $1 million. Insurance was unlikely to cover any damage as subsidence in such circumstances was predictable.

Two public meetings will be held in Taupo this week to discuss the issue while the council and Environment Waikato plan to meet with Contact Energy and the Geotherm Group next month.

What's at stake

A report for Taupo District Council raises questions about the effects of extracting geothermal energy on buildings in the lakeside town.

What is predicted?

Subsidence will affect some Taupo buildings within 50 years. Foundations, framing, roofs, floors and walls could be damaged; windows and doors could stick.

What will be affected?

More than 150 buildings including 24 houses, the Spa Hotel, council dog pound, Tauhara College, Fletcher Challenge sawmill and Owen Delany Park grandstands.

What has caused it?

Experts blame the extraction of geothermal energy from underground.

Who's involved?

Contact Energy has extracted heat and water from the Wairakei-Tauhara field since 1998. State-owned ECNZ had previously done so since the 1950s. Another company, Geotherm Group, wants permission to build a new power station there.