Preventing geothermal discharge
At Ngāwhā the geothermal fluids used to generate electricity are returned to the deep geothermal reservoir via re-injection wells. This practice not only prevents geothermal fluid discharge into the environment (where adverse effects would occur) but also maintains reservoir fluid mass. This in turn enhances the long term sustainability of the geothermal resource as well as minimising the possibility of any surface subsidence.
Protecting our native flora and fauna
The Ngāwhā geothermal site is home to many native bird, fish and plant life and Ngawha Generation Limited is committed to preserving these through its ongoing ecological monitoring.
Native New Zealand birds, include Tomtit, Fantail, Pipit, NZ Brown Kiwi and the Fernbird (Matata). The North Island Fernbird is classified as ‘sparse’ by the Department of Conservation and, although difficult to find, has been identified at the Ngāwhā geothermal site.
The North Island Mudfish, classified as ‘critically endangered’ can only be found in the wetlands near the Kerikeri Airport and at Ngawha. Eels can also be found onsite, living in the outer-lying waterways (receiving waters) at Ngāwhā.
The native Sun Orchid, a pretty flowering plant, and Sedge (Baumea complanta) a plant that is only found in the Ngāwhā wetlands, both thrive at the Ngāwhā geothermal site.
Environmental management
Ngāwhā geothermal power station operates a comprehensive environmental management plan and environmental monitoring to preserve the natural resources, the underground reservoir and the natural waterways. Environmental monitoring measures include:
- Ecology The ecology of the Ngāwhā geothermal site is monitored, including the native New Zealand Sun Orchids, Sedge, North Island Fern Bird, North Island Mudfish; and the Green and Gold Bell Frog, originally from Australia in the 1860s.
- Receiving Waters Receiving waters (waterways that naturally drain away from the site) are monitored for levels of geothermal discharge in both the water and sediment.
- Ground Water Ground Water is located beneath the earth surface and is monitored for any change in its chemistry. This is one way of checking if there are any leaks from the ponds that have been built as part of the project. The ponds contain any geothermal discharges from the power station and well platforms and also rainfall that may drain off the site.
- Atmosphere Weather stations are located in Ngāwhā Village and at the northern side of the power station. These collect information on rainfall, temperature, relative humidity, solar radiation, wind direction and wind speed. Atmospheric monitoring measures the hydrogen sulphide levels in the air. Hydrogen sulphide occurs from both natural features (such as the Ngāwhā Springs) and also from the power station operations.
- Subsidence Subsidence monitoring is carried out every five years to determine if there is any change to the ground level arising from the electricity generation activities.
- Ngāwhā Hot Springs The Ngāwhā Hot Springs are fed from the same geothermal reservoir as the power station. The hot springs are monitored to ensure there is no detrimental impact on the water chemistry and temperature.
- Lakes The natural lakes near the site are monitored to determine whether there are any effects caused by the power station.
- Production Well Samples are taken from the Ngāwhā wells to analyse the chemistry of the geothermal brine and steam. This monitoring measures the ‘enthalpy’ (i.e. the energy potential from the brine and steam).
- Reinjection Well The fluid that is reinjected into the Ngāwhā reservoir is monitored for any change in the chemistry. This information is used to help tune the operation of the station.
If there is a change to any of these characteristics, the effect is traced back to find the root cause then taken into consideration in the operational and environmental management of the site.
Sediment and erosion control during construction of the new station
As part of any earthworks, sediment and erosion control was achieved using temporary settling ponds for treating rain water runoff and revegetation of disturbed surfaces with suitable plants. Plants hold the soil on the banks (erosion control) and provide a natural filtration system (sediment control); as water containing small particles could flow from the site as a result of rainfall. Sediment control is important so that soil and other materials do not flow into natural waterways around the site, which could have a negative effect on native fish.
