Environmental management practices at the Ngawha geothermal plant are monitored by independent environmental specialists and reported under consent conditions to Northland Regional Council.
A comprehensive environmental effects report was prepared as part of the resource consenting process for the Ngawha expansion, and resource consent was granted in July 2017.
At Ngawha 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.
The Ngawha 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 Ngawha 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 Ngawha.
The native Sun Orchid, a pretty flowering plant, and Sedge (Baumea complanta) a plant that is only found in the Ngawha wetlands, both thrive at the Ngawha geothermal site.
Ngawha 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:
||The ecology of the Ngawha 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 (waterways that naturally drain away from the site) are monitored for levels of geothermal discharge in both the water and sediment.
||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.
||Weather stations are located in Ngawha 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 Ngawha Springs) and also from the power station operations.
||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.
|Ngawha Hot Springs
||The Ngawha 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.
||The natural lakes near the site are monitored to determine whether there are any effects caused by the power station.
||Samples are taken from the Ngawha 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).
||The fluid that is reinjected into the Ngawha 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.
As part of any earthworks, sediment and erosion control is 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.