Wainui is a small, largely holiday settlement with a current permanent population of 111 residents (Census 2013). Peak population levels are 700–800 persons during a three week period in December–January.
There are approximately 160 homes in total, of which 60 house the permanent residents.
Wastewater from the 34 properties comprising the subdivision in Seaview Lane are serviced by a small treatment plant built by the developer which, until 2013, discharged treated wastewater into Akaroa Harbour. All other properties in the Wainui settlement are serviced by private septic tanks, long drops or storage tanks.
Stage One of the Wainui Wastewater Reticulation and Treatment Scheme has seen treated wastewater from the Seaview Lane Wastewater Treatment Plant diverted from Akaroa Harbour to a Council-owned land discharge in the forestry block above Warnerville Road. This work was completed in May 2013. This removed the treated wastewater from the Harbour.
The second stage of the Scheme is to provide the rest of the residents with a reticulated wastewater disposal system. The proposed Scheme is a low pressure sewer system using small on-property pressure grinder pumps to pump untreated wastewater from each property to a new treatment plant located near the top of Warnerville Road. Treated discharge from this plant will be irrigated on the Council-owned forestry block. This Stage also includes the diversion of wastewater from the properties comprising the Seaview Lane subdivision from the Seaview Lane Wastewater Treatment Plant, which is located on private property, to the new treatment plant at the top of Warnerville Road. This would allow for the decommissioning and removal of Seaview Lane Wastewater Treatment Plant and the return of the land to its owner.
Stage Two work was scheduled to begin in October 2014. This has now been put on hold while the Council seeks the views of Wainui residents, and the wider community, on possible future options for the delivery of the Scheme.
Why the Scheme was proposed
Many homes in Wainui settlement have long-drops, septic tanks or storage tanks for the disposal of their wastewater. Issues can arise with these systems especially with older systems, some of which can be more than 50 years old. For example, septic tanks have a land-based effluent discharge. With heavy or prolonged rain, effluent has the potential to leech into waterways and enter the Harbour.
There are approximately 126 properties with either long-drops, septic tanks or storage tanks. Monitoring of water quality in Wainui Bay is carried out by Environment Canterbury (ECan) regularly in the summer holiday period. ECan monitoring grades the Harbour water as ‘good’ and does not show any marked impacts of these disposal systems on the Harbour water quality, except following wet weather events when bacterial numbers in the water are higher.
The main environmental issue, to remove treated wastewater discharge into Akaroa Harbour, was addressed successfully in Stage One of the Wainui Wastewater Reticulation and Treatment Scheme.
Main benefits of the Scheme
A pressure sewer reticulated wastewater disposal system is well suited for low density semi-rural communities and rural landscape. It consists of a pumping unit housed in a plastic holding tank which is buried on a property. The holding tank receives wastewater from a house, which is then pumped into the wastewater network and up to the new treatment plant.
With this system there is minimal chance of leakages or overflows. Therefore, it is an environmentally-friendly option. Existing and new properties in the townships will be able to install the pumping unit and holding tank, and connect to the wastewater network. This is a sustainable and resilient option in the long-term for managing the wastewater in a spread-out and growing community.
Settlements of the Akaroa Harbour Basin
Christchurch City Council has undertaken a strategic planning study of the settlements of the Akaroa Harbour Basin.
The purpose of this study was to take an integrated, long-term view (25–30 years) of land use change and other issues within the settlements of the harbour basin and incorporate the local community's preferences on how future land use changes should be managed. To find out more, and what this study says about Wainui’s future development(external link).
Wainui Wastewater Reticulation and Treatment Scheme timeline
The Banks Peninsula Community Plan, current in September 2004, indicated that detailed investigations for the Wainui Sewerage Scheme would be completed in the 2006/07 financial year.
|2006–2014||The Scheme is included in the Banks Peninsula District Council’s 2006 Long Term Council Community Plan (LTCCP), the Council’s LTCCP and the Council’s Christchurch City 2013 Three Year Plan.|
|2011||A resource consent for the new plant and discharge to land obtained from Environment Canterbury (ECan).|
|2012||A report from GHD Consultants confirmed that a pressure wastewater system was the recommended option for Wainui because of technical, cost, environmental and resilience reasons.|
|June 2012–2014||Ongoing communication with property owners about the timeframe for the Scheme. Approximately 95 per cent of landowners have provided the Council with consent forms for the system to be installed on their property.|