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Published: 2004-10-15 00:00:00

Environment Waikato has granted Contact Energy Ltd resource consents to allow the company to continue operating its Wairakei and Poihipi geothermal power stations near Taupo until 2026 - but with conditions requiring it to clean up its discharge into the Waikato River and stop subsidence in Taupo.

In March 2001 Contact applied to Environment Waikato and Taupo District Council for 25 consents to continue operating the stations which rely on extraction of geothermal fluid from the Wairakei-Tauhara Geothermal System. All but one of the consents have been granted by a panel of independent Commissioners.

It is the first time that the environmental effects of the Wairakei Power Station have been subject to public scrutiny since the plant commenced operations in 1958. The application attracted 200 submissions from Taupo District Council, DoC, Fish and Game, Watercare Services, local iwi groups, landowners, Mighty River Power and Wairakei Thermal Valley.  About 180 submissions opposed the application, three supporting and the rest neutral.

Taupo District Council said extraction of geothermal fluid at Wairakei was causing subsidence and property damage in Taupo, particularly in the Crown Road-Invergarry Road area. Other submitters, including Auckland water supplier Watercare Services, opposed discharge of separated geothermal water and cooling water into the Waikato River and said all geothermal fluid should be re-injected into the ground within the geothermal system.

Other submitters were concerned about the potential effects of re-injecting geothermal fluid outside the geothermal field, which they said could contaminate groundwater used for domestic and stock purposes. Contact said it did not favour large scale re-injection of geothermal fluid, as that it would lead to a shortening of the life of the geothermal field.

The hearing took more than 30 days over four months. Overseas expert witnesses presented detailed evidence about the geothermal system and the effects of Contact’s take.

The Committee decided that, although there was significant uncertainty, it was "more likely than not" that Contact’s extraction of geothermal fluid had reduced underground pressure which was causing subsidence and property damage.

The Committee decided not to require targeted injection in the Crown Road area as it had no legal power to do so and because there were potential risks. It ordered Contact to re-inject into an area between the Wairakei and Tauhara lobes of the geothermal system to raise pressures and eliminate the cause of future subsidence, and to set up a special claims procedure to deal with property damage.

A $1 million mitigation package for unavoidable adverse ecological and geothermal effects is required as well as a mitigation package that recognises and seeks to address effects on Maori cultural and spiritual values relating to past and future operation of the steam field.

The Committee required substantially reduced levels of hydrogen sulphide, arsenic, mercury and heat discharges from the Wairakei plant into the Waikato River to be implemented throughout the term of the consents. It limited re-injection to the same quantities and the same locations as allowed under existing consents which expire in 2011 and 2013.

It said increased injection within the geothermal field required to address subsidence issues may have a minor impact on the geothermal reservoir and on some surface features but the importance of addressing the subsidence issue outweighed these other factors.

"The decisions we have made strike an appropriate balance between the economic, social, environmental and cultural considerations, having regard to the sustainable management requirements of the Resource Management Act," it said.