Formalities for Kawakawa Bay Wastewater Scheme
22 May 2006
Formalities Give Sanction to Kawakawa Bay Wastewater Scheme
Kawakawa Bay’s wastewater scheme received the official nod with a formal sod-turning ceremony on Wednesday.
The scheme will provide the Kawakawa Bay community with an advanced wastewater collection treatment and disposal system.
Wednesday’s ceremony was carried out by the Mayor of Manukau City, Sir Barry Curtis and Iwi Representatives of Ngai Tai Umupuia and Ngati Paoa.
Sir Barry said the plant is the first of its kind in New Zealand.
“But, I must stress that it should not be seen as an opportunity to increase the population of Kawakawa Bay. Instead, regional and district planning policies will determine whether any growth in population is necessary.”
The system will serve both the current population of about 600, as well as the around 3000 population projected for the bay by 2050.
Construction will begin as soon as consents are granted, with December 2007 the targeted operational date.
The scheme will be built on the Glen Forest Block, which will also serve for the land disposal system. Because of the high-quality treatment involved, the spray irrigation dispersal will have minimal environmental impacts.
as a contingency, Manukau Water will apply for resource
consent to discharge the treated effluent to a tributary of
the Rautawa Stream, via an overland flow and rock filter.
Any stream discharge would be rare, with rainfall analysis
indicating such a discharge would have been necessary once
only in the past 32 years. The system also provides for up
to 30 days storage of treated effluent to allow for
excessively wet periods when irrigation may not be possible.
Manukau Water general manager Raveen Jaduram says the environmental effects of such a discharge to the stream would be negligible to non-existent, because of the high level of treatment.
“This scheme will be of huge benefit to the Kawakawa Bay community and will address the existing public health and environmental issues,” Mr Jaduram says.
“We also want to acknowledge the efforts, co-operation and active support of the community, Iwi representatives of Nga Tai Umupuia and Ngati Paoa and other key stakeholders,” he says.
In July 2002 a significant health risk was identified for the Kawakawa Bay community due to the contamination of water bodies by poorly performing on-site disposal systems. Manukau City Council’s Strategic Committee resolved in September 2003 to provide a public wastewater collection, treatment and disposal system to meet the statutory requirements of the Health Act 1956.
Manukau City Council purchased 150 Ha forest known as the Glen Forest Block for $2.7M in 2005 and this will be the location of both the wastewater treatment plant and the land disposal system.
The project has an overall cost of $18 Million, with the bulk of the physical construction works to be carried out by Fulton Hogan Ltd, one of New Zealand’s largest contractors.
The scheme is programmed to be operational by December 2007, and will serve both the current population of approximately 600 people as well as the projected (2,050) future population of 3,000.
The wastewater scheme includes several innovative components:
a vacuum based
membrane based wastewater treatment plant – which produces a very high quality effluent;
land disposal / treatment using spray irrigation in the forest.
Of note is the treatment plant that will be constructed for the scheme as it uses cutting edge membrane treatment technology. The effluent goes through fine membranes, similar to those; these membranes are very fine and similar to the membranes they use in the Waikato Water Treatment Plant. These membranes produce a very high quality effluent compared to conventional wastewater treatment plants and as a result the effluent does not need any further disinfection.
Impact on the environment will be minimal because the proposed spray irrigation system will disperse the effluent across the Glen Forest. The forest will dispose of the water and use the remaining nutrients in the treated effluent. The system also provides for up to 30 days storage of treated effluent to allow for excessively wet periods when irrigation may not be possible.
As a contingency Manukau Water will also be applying for resource consent to discharge treated effluent to a tributary of the Rautawa Stream, via an overland flow and rock-filter. This discharge will only be used as a contingency, as the investigations and modelling have confirmed that the need for a stream discharge would be a very rare occurrence i.e. analysis of the last 32 years of rainfall data indicates that a discharge to the stream would have been required only once in the past 32 years. The environmental effects of this discharge will be negligible to non-existent. As a comparison, similar systems in Australia dispose of their treated effluent straight onto the Great Barrier Reef.