The Future of Wastewater in Lyttelton Harbour
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The Christchurch City Council, in conjunction with the Lyttelton Harbour Wastewater Working Party Lyttelton Wastewater Working Party is exploring options for wastewater treatment and disposal for the Diamond Harbour, Governors Bay and Lyttelton communities.
Two Preferred Options for managing the Harbour's wastewater have been identified and community feedback has been sought on these options prior to any further investigations being carried out.
Background
This project has been designed to meet the requirements of the Environment Canterbury Resource Consent (CRC031546) conditions 19 to 24 placed on the existing discharge from the Diamond Harbour, Governors Bay and Lyttelton Wastewater Treatment Plants.
Currently wastewater from homes and businesses in Lyttelton Harbour is carried through a network of underground pipes and pumps to treatment plants at Lyttelton, Governors Bay and Diamond Harbour.
Following treatment the wastewater is discharged into the Harbour. Sewage sludge, a by-product of the sewage collection and treatment process, is carried by truck to the Christchurch Wastewater Treatment Plant for further treatment and disposal.
The next five years will see the entire Lyttelton Harbour community connected to the wastewater system. Population growth, an ageing infrastructure and increased public expectation about environmental standards mean changes are required to how the Harbour's wastewater is managed in the future.
Lyttelton Wastewater Working Party
The Lyttelton Harbour Wastewater Working Party was established in 2005 to evaluate a range of future treatment and disposal options for wastewater currently discharged from the Diamond Harbour, Governors Bay and Lyttelton wastewater treatment plants.
The Working Party includes representatives from the Department of Conservation, Environment Canterbury, Ngai Tahu, Community and Public Health, and local residents with an interest in local environmental and welfare issues.
The Working Party Goals are:
- To ensure wastewater does not harm the marine environment of the harbour basin
- To remove wastewater from Lyttelton Harbour and any other local waterway
- To have treatment and disposal systems that support the economic success of the area
- To recognise the links between people, the environment and wastewater management
- To recognise wastewater can be a resource and reuse it where possible
- To ensure recreation in the harbour is not affected by wastewater
- To achieve compliance with appropriate Acts, Plans and standards
Following careful analysis and discussion, the Working Party, in conjunction with the Council's project team, has selected Preferred Options which they are seeking community feedback on.
Preferred Options
After evaluating nine different options All Options Considered by the Working Party for the treatment and disposal of wastewater, the Working Party have identified two preferred options for further investigation.
Under the Council's funding policy the capital costs for whichever option is finally selected will be borne across all Christchurch City ratepayers.
 1) Application of Treated Wastewater to Land
Wastewater would be treated at one or more of the existing treatment plants and then used to irrigate specific areas of land.
Under this approach treated wastewater is viewed as a resource which could provide economic benefits to the local community through the harvest and sale of crops such as timber.
Land disposal of treated wastewater has been implemented successfully overseas and in places such as Rotorua and Tikao Bay in New Zealand.
Further work on land disposal of treated wastewater could investigate appropriate crops and ways of maximising economic and environmental benefit.
 2) Utilise the Christchurch Wastewater Treatment Plant
Under this option, untreated wastewater would be pumped under the Ocean from both Diamond Harbour and Governors Bay to Lyttelton, and then taken via tunnel to the Christchurch Wastewater Treatment Plant (CWTP) in Bromley.
The wastewater would be treated at the CWTP and then discharged through the new Ocean Outfall three kilometres out into Pegasus Harbour.
This option utilises existing capacity and technology at the CWTP. Treated wastewater would be completely removed from Lyttelton Harbour and diffused into a much larger marine environment via the Ocean Outfall.
Also under investigation
A combination of the above options may also be investigated.
The option of improving the quality of wastewater discharged into the Harbour by upgrading the current Harbour treatment plants will be investigated to provide a benchmark on costs.
All Options Considered by the Working Party
The Lyttelton Harbour Wastewater Working Party evaluated nine different options for the treatment and disposal of Lyttelton Harbour wastewater.
Option 1A - Maintaining Existing Treatment Plants with Existing Quality
This option involved maintaining the current situation by continuing to treat wastewater at the three existing wastewater treatment plants and discharging wastewater to Lyttelton Harbour via the existing outfalls. The wastewater treatment plants would be upgraded to increase their capacity, but the current wastewater quality consent conditions would be maintained, hence no improvement in effluent quality would be provided.
Option 1B - Maintain Existing Plants with Improved Quality
This option involved continuing to treat and discharge wastewater from the three existing wastewater treatment plants and outfalls, with improved effluent quality to meet stricter effluent quality consent conditions. The wastewater treatment plants would be upgraded both to increase capacity and to improve quality.
While failing to meet the Working Party's goals, this option will be further investigated to provide a benchmark for costs.
Option 2A - Centralised Treatment at Lyttelton with Existing Quality
This option involved centralising wastewater treatment and disposal at the Lyttelton Wastewater Treatment Plant. Wastewater from the Diamond Harbour and Governors Bay catchments would be pumped to Lyttelton for treatment and disposal, and the Diamond Harbour and Governors Bay treatment plants would be decommissioned. The Lyttelton wastewater treatment plant would be upgraded to handle the increased load but the current wastewater quality would be maintained.
Option 2B - Centralised Treatment at Lyttelton with Enhanced Quality
This option involved centralising wastewater treatment and disposal at the Lyttelton Wastewater Treatment Plant, with improved effluent quality compared to the existing quality. Wastewater from the Diamond Harbour and Governors Bay catchments would be pumped to Lyttelton for treatment and disposal, and the Diamond Harbour and Governors Bay treatment plants would be demolished. The Lyttelton Wastewater Treatment Plant would be upgraded to handle the increased loads and to produce improved effluent quality to meet stricter effluent quality consent conditions.
Option 3 - Re-Use of Treated Wastewater
This option involved continuing to treat wastewater at the three existing wastewater treatment plants, however the plants would be upgraded to become recycled water plants, producing high quality treated wastewater suitable for re-using within the urban environment.
Recycled water reticulation systems would be constructed to pump the recycled water back to the communities and distribute it to end users. It was assumed the most viable options for reuse of waste water are that at Lyttelton the recycled water is used for coal stockpile dust suppression, and at Governors Bay and Diamond Harbour the recycled water is used for private garden watering/outdoor use, toilet flushing and public space irrigation.
Option 4A - Land Disposal of Treated Wastewater
This option involves disposing all of the treated wastewater from the Lyttelton Harbour Basin to land, via irrigation onto pasture. Wastewater would continue to be treated at the three existing treatment plants. Pump stations and pipes would transfer treated wastewater from the treatment plants to land disposal areas.
The Working Party are interested in investigating this option further.
Option 4B - Treated Wastewater Disposal to Ground
This option would involve disposing of the treated wastewater from each or all of the wastewater treatment plants into a deep borehole.
Option 4C - Pump Wastewater to the Christchurch Wastewater Treatment Plant
This option involves pumping untreated wastewater from the three wastewater catchments to the main reticulation network, where it would combine with Christchurch wastewater and be conveyed to the Christchurch Wastewater Treatment Plant for treatment and will be discharged into Pegasus Bay via a new 3 kilometre ocean outfall.
The Working Party are interested in investigating this option further.
Option 4D - Centralised Treatment at Lyttelton Wastewater Treatment Plant with New Ocean Outfall
This option involves centralising wastewater treatment and disposal at the Lyttelton Wastewater Treatment Plant, with disposal into Pegasus Bay via a new extended outfall from Lyttelton to 3 km beyond the harbour heads. View Ocean Outfall.
For more information on any of these options visit MWH Report into Options for Lyttelton Harbour Wastewater Treatment.
What happens next?
Having arrived at a consensus on the preferred options feedback from Harbour Communities has been received.
Following the analysis of this feedback the Council will undertake more detailed investigations including concept design and detailed cost estimates.
It is expected that a formal public consultation process will take place later in 2008 when these options have been investigated in more detail.
Questions and Answers
Why was the project set up?
This project has been designed to meet the requirements of the ECan Resource Consent (CRC031546) conditions 19 to 24 placed on the existing discharge from the Diamond Harbour, Governors Bay and Lyttelton Wastewater Treatment Plants.
What happens at present?
Under the current situation, sewage is pumped to the treatment plants at Lyttelton, Governors Bay and Diamond Harbour. Treated wastewater is then discharged to the Harbour via 3 separate pipelines.
Approximately 95% of residents are linked up to the sewage system, the rest on septic tanks. The current situation with the existing wastewater systems will not comply with future consent conditions.
What are you trying to achieve?
The main objective of the project is to find the most cost-effective and environmentally acceptable method of waste water disposal for Diamond Harbour, Governors Bay and Lyttelton communities.
What has happened to date?
The Working Party documented nine possible options to be investigated.
Through an open tender, the Council appointed Consultants MWH NZ Ltd to put together feasibility studies of technical options.
After reviewing the information the Working Party selected three options to be considered for further investigation. These are:
- Application of treated wastewater to land.
- Pumping wastewater to the Christchurch Wastewater Treatment Plant.
- Maintain the existing treatment plants but upgrade infrastructure to improve water quality and therefore meet future consent requirements. While failing to meet the Working Party's goals, this option will be further investigated to provide a benchmark for costs.
What happens next?
Following community feedback on the preferred options, the Council (and consultants) will proceed with a more detailed investigation of the options including concept design and cost estimates.
It is expected that a formal public consultation process will take place later in 2008 when these options have been investigated in more detail.
Who will bear the cost?
Under the Council's funding policy the capital costs for whichever option is finally selected will be borne across all Christchurch rate payers.
Links
Contact Us
Please feel free to email any comments to lytteltonwastewater@ccc.govt.nz or contact Matt Cummins (Project Manager) on 03 941 8236 |
