Ngawha geothermal power station operates a comprehensive environmental management plan driven by Top Energy’s commitment to preserving the natural resources and by the conditions of the Northland Regional Council’s resource consents, which the power station operates under.
The high level objective of environmental monitoring is to “preserve the natural resources: the reservoir and the natural waterways”. At an operational level, environmental monitoring measures if there is any change to key characteristics of the site, including:
|Ecology||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||Receiving Waters are the waterways that drain away from the site. These are monitored for levels of geothermal discharge in both the water and sediment. Clean waterways are important for ecology, including supporting fish and bird life.|
|Ground Water||Ground Water is located beneath the earth surface and is monitored to check the integrity of the water, looking for any change in its chemistry. This is one way of checking to ensure the structure of the ponds is intact and whether there are any leaks from the ponds. The ponds contain any geothermal discharges and also rainfall, that may drain off the site.|
|Atmosphere||A weather station is located in Ngawha Village and collects 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 naturally from both natural features (such as the Ngawha 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.|
|The Ngawha Hot Springs are fed from the same geothermal reservoir as the power station, so the hot springs are monitored to ensure there is no detrimental impact on the hot springs 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 Ngawha Production Wells to analyse the chemistry of the geothermal brine and steam. This monitoring measures the ‘enthalpy’ (ie the energy potential from the brine and steam).|
|Reinjection Well||The fluid that is reinjected into the Ngawha reservoir is monitored for any change in the chemistry.|
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
As part of any earthworks, revegetation is managed with suitable plants to provide sediment and erosion control. 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, having a negative effect on native fish.